• 1. 计算机专业英语教程2010.5.1
  • 2. Computer English Chapter 1 The History and Future of ComputersComputer science major course
  • 3. As a computer science student,we should study English hard This book is very important to us 3
  • 4. Key points: useful terms and definitions of computers Difficult points: describing the features of computers of each generation4
  • 5. Requirements:1. The trends of computer hardware and software 2. Basic characteristics of modern computers 3. Major characteristics of the four generations of modern computers 4. 了解科技英语的特点,掌握科技英语翻译要点 5
  • 6. New Words & Expressions: computerlike a. 计算机似的 electromechanical a. 机电的, 电机的 vacuum tubes 真空管 Census Bureau 人口普查局 thousands of 成千上万的 known as 通常所说的,以……著称 1.1 The Invention of the Computer Abbreviations: ENIAC(Electronic Numerical Integrator and Computer) 电子数字积分计算机,ENIAC计算机 EDSAC (Electronic Delay Storage Automatic Computer) 延迟存储电子自动计算机 BINAC (Binary Automatic Computer) 二进制自动计算机 UNIVAC (Universal Automatic Computer) 通用自动计算机 6
  • 7. It is hard to say exactly when the modern computer was invented. Starting in the 1930s and through the 1940s, a number of machines were developed that were like computers. But most of these machines did not have all the characteristics that we associate with computers today. These characteristics are that the machine is electronic, that it has a stored program, and that it is general purpose. 很难确切地说现代计算机是什么时候发明的。从20世纪30年代到40年代,制造了许多类似计算机的机器。但是这些机器大部分没有今天我们所说的计算机的所有特征。这些特性是:机器是电子的,具有储存的程序, 而且是通用的。1.1 The Invention of the Computer 7
  • 8. 1.1 The Invention of the Computer One of the first computerlike devices was developed in Germany by Konrad Zuse in 1941. Called the Z3, it was general-purpose, stored-program machine with many electronic parts, but it had a mechanical memory. Another electromechanical computing machine was developed by Howard Aiken, with financial assistance from IBM, at Harvard University in 1943. It was called the Automatic Sequence Control Calculator Mark I, or simply the Harvard Mark I. Neither of these machines was a true computer, however, because they were not entirely electronic. 第一个类似计算机的装置之一是1941年由德国的Konrad Zuse研制的,叫做Z3,它是通用型储存程序机器,具有许多电子部件,但是它的存储器是机械的。另一台机电式计算机器是由霍华德.艾坎在IBM的资助下于1943年在哈佛大学研制的。它被称为自动序列控制计算器Mark I,或简称哈佛Mark I。然而,这些机器都不是真正的计算机,因为它们不是完全电子化的。 8
  • 9. 1.1.1 The ENIAC Perhaps the most influential of the early computerlike devices was the Electronic Numerical Integrator and Computer, or ENIAC. It was developed by J. Presper Eckert and John Mauchly at the University of Pennsylvania. The project began in 1943 and was completed in 1946. The machine was huge; it weighed 30 tons and contained over 18,000 vacuum tubes. 也许早期最具影响力的类似计算机的装置应该是电子数字积分计算机,或简称ENIAC。它是由宾夕凡尼亚大学的J. Presper Eckert 和John Mauchly 研制的。该工程于1943年开始,并于1946年完成。这台机器极其庞大,重达30吨,而且包含18,000多个真空管。1.1 The Invention of the Computer 9
  • 10. 1.1.1 The ENIAC The ENIAC was a major advancement for its time. It was the first general-purpose, electronic computing machine and was capable of performing thousands of operations per second. It was controlled, however, by switches and plugs that had to be manually set. Thus, although it was a general-purpose electronic device, it did not have a stored program. Therefore, it did not have all the characteristics of a computer . ENIAC是当时重要的成就。它是第一台通用型电子计算机器,并能够执行每秒数千次运算。然而,它是由开关和继电器控制的,必须手工设定。 因此,虽然它是一个通用型电子装置,但是它没有储存程序。 因此,它不具备计算机的所有特征。 1.1 The Invention of the Computer 10
  • 11. 1.1.1 The ENIAC While working on the ENIAC, Eckert and Mauchly were joined by a brilliant mathematician, John von Neuman. Together, they developed the idea of a stored program computer. This machine, called the Electronic Discrete Variable Automatic Computer, or EDVAC, was the first machine whose design included all the characteristics of a computer. It was not completed, however, until 1951. 在ENIAC的研制中,一个天才的数学家Von Neuman(冯.诺伊曼)加入到 Eckert和Mauchly团队,他们一起提出了储存程序计算机的主意。这部机器被称做电子离散变量自动计算机, 或简称EDVAC,是第一部包括了计算机所有特征的机器。然而,直到1951年,它一直没有完成。 1.1 The Invention of the Computer 11
  • 12. 1.1.1 The ENIAC Before the EDVAC was finished, several other machines were built that incorporated elements of the EDVAC design of Eckert, Mauchly, and von Neuman. One was the Electronic Delay Storage Automatic Computer, or EDSAC, which was developed in Cambridge, England. It first operated in May of 1949 and is probably the world’s first electronic stored-program, general-purpose computer to become operational. The first computer to operate in the United States was the Binary Automatic Computer, or BINAC, which became operational in August of 1949. 在EDVAC完成之前,其他一些机器建成了,它们吸收了Eckert、Mauchly和Neuman设计的要素。其中一部是在英国剑桥研制的电子延迟存储自动计算机,或简称EDSAC,它在1949年5月首次运行,它可能是世界的第一台电子储存程序、通用型计算机投入运行。在美国运行的第一部计算机是二进制自动计算机,或简称BINAC,它在1949年8月投入运行。 1.1 The Invention of the Computer 12
  • 13. 1.1 The Invention of the Computer 1.1.2 The UNIVAC I Like other computing pioneers before them, Eckert and Mauchly formed a company in 1947 to develop a commercial computer. The company was called the Eckert-Mauchly Computer Corporation. Their objective was to design and build the Universal Automatic Computer or UNIVAC. Because of difficulties of getting financial support, they had to sell the company to Remington Rand in 1950. Eckert and Mauchly continued to work on the UNIVAC at Remington Rand and completed it in 1951. Known as the UNIVAC I, this machine was the first commercially available computer. 像他们之前的其他计算机先驱一样,Eckert和Mauchly在1947年组成了一家公司开发商业计算机。公司名叫Eckert-Mauchly计算机公司。他们的目标是设计并建造通用自动计算机或UNIVAC。因为难以获得财政支持,他们不得不在1950年把公司卖给了Remington Rand公司。Eckert 和Mauchly继续在Remington Rand公司从事UNIVAC的研制工作,并在1951年取得成功。众所周知的UNIVAC I机器是世界上第一部商业化计算机。13
  • 14. 1.1 The Invention of the Computer 1.1.2 The UNIVAC I The first UNIVAC I was delivered to the Census Bureau and used for the 1950 census. The second UNIVAC I was used to predict that Dwight Eisenhower would win the 1952 presidential election, less than an hour after the polls closed. The UNIVAC I began the modern of computer use. 第一台UNIVAC I被交付人口普查局用于1950年的人口普查。在投票点关闭后1小时之内,第二台UNIVAC I 被用于预测D.艾森豪威尔会赢得1952年总统大选。UNIVAC I开始了现代计算机的应用。14
  • 15. New Words & Expressions: result in 导致, 造成……结果 air conditioning 空气调节 take delivery of 正式接过… Navy lieutenant 海军上尉 high-level language 高级语言 mainframe n. 主机, 大型机 more and more 越来越多的 range from …to… 从…到… multiprogramming n.多道程序设计 time-share n.分时,时间共享 virtual memory 虚拟内存 from scratch 从头开始 compatible a. 兼容的; compatibility n. 兼容性 outnumber vt. 数目超过,比…多 proliferate v. 增生,扩散 start off v. 出发, 开始 1.2 Computer Generations Abbreviations : VLSI (Very Large Scale Integrated Circuit) 超大规模集成电路 LSI (Large Scale Integrated Circuit) 大规模集成电路 DEC (Digital Equipment Corporation) 美国数字设备公司 COBOL (Common Business-Oriented Language) 面向商业的通用语言15
  • 16. 1.2 Computer Generations 1.2.1 First-Generation Computers: 1951~1958 First-generation computers were characterized by the use of vacuum tubes as their principal electronic component. Vacuum tubes are bulky and produce a lot of heat, so first-generation computers were large and required extensive air conditioning to keep them cool. In addition, because vacuum tubes do not operate very fast, these computers were relatively slow. 第一代计算机的特色是使用真空管为其主要电子器件。真空管体积大且发热严重,因此第一代计算机体积庞大,并且需要大量的空调设备保持冷却。此外, 因为真空管运行不是很快,这些计算机运行速度相对较慢。 The UNIVAC I was the first commercial computer in this generation. As noted earlier, it was used in the Census Bureau in 1951. It was also the first computer to be used in a business application. In 1954, General Electric took delivery of a UNIVAC I and used it for some of its business data processing. UNIVAC I是第一代中最早的商业化计算机。如前所述,它在1951年被用于人口普查局。它还是第一部用于商业应用的计算机。在1954年,通用电气接收了UNIVAC I,并用它进行一些商业数据处理。 16
  • 17. 1.2 Computer Generations 1.2.1 First-Generation Computers: 1951~1958 The UNIVAC I was not the most popular first-generation computer, however. This honor goes to the IBM 650. It was first delivered in 1955 before Remington Rand could come out with a successor to the UNIVAC I. With the IBM 650, IBM captured the majority of the computer market, a position it still holds today. 然而,UNIVAC I并不是最流行的第一代计算机。这一荣誉属于IBM 650。它在Remington Rand能够造出UNIVAC I的后续产品之前的1955年首次交付使用。凭借IBM 650,IBM占有了大半计算机市场,它在今天仍然保持这一位置。17
  • 18. 1.2 Computer Generations 1.2.1 First-Generation Computers: 1951~1958 At the same time that hardware was evolving, software was developing. The first computers were programmed in machine language, but during the first computer generation, the idea of programming language translation and high-level languages occurred. Much of the credit for these ideas goes to Grace Hopper, who, as a Navy lieutenant in 1945, learned to program the Harvard Mark I. In 1952, she developed the first programming language translator, followed by others in later years. She also developed a language called Flow-matic in 1957, which formed the basis for COBOL, the most commonly used business programming language today. 同时,硬件在进化,软件也在发展。第一部计算机用机器语言编程,但是在第一代计算机期间,程序语言翻译的概念和高级语言出现了。这些主意大部分归功于Grace Hopper,她在1954年是一名海军上尉,学习为哈佛Mark I计算机编程。在1952年,她开发了第一种编程语言翻译器,在稍后的数年内为其他人所效仿。她还在1957年开发了一种称为Flow-matic的语言,为COBOL——今天最广泛应用的商业编程语言——奠定了基础。18
  • 19. 1.2 Computer Generations 1.2.1 First-Generation Computers: 1951~1958 Other software developments during the first computer generation include the design of the FORTRAN programming language in 1957. This language became the first widely used high-level language. Also, the first simple operating systems became available with first-generation computers. 在第一代计算机期间, 软件方面的其他的进展包括1957年FORTRAN语言的设计。这种语言成为第一种广泛使用的高级语言。同时, 第一个简单的操作系统随着第一代计算机而出现。19
  • 20. 1.2 Computer Generations 1.2.2 Second-Generation Computers: 1959~1963 In the second generation of computers, transistors replaced vacuum tubes. Although invented in 1948, the first all-transistor computer did not become available until 1959. Transistors are smaller and less expensive than vacuum tubes, and they operate faster and produce less heat. Hence, with second-generation computers, the size and cost of computers decreased, their speed increased, and their air-conditioning needs were reduced. 在第二代计算机中,晶体管取代了真空管。虽然发明于1948年,但第一台全晶体管计算机直到1959年才成为现实。晶体管比真空管体积小、价格低,而且运行快而发热少。因此,随着第二代计算机的出现,计算机的体积和成本降低、速度提高,且它们对空调的需要减少。 Many companies that had not previously sold computer entered the industry with the second generation. One of these companies that still makes computers is Control Data Corporation (CDC). They were noted for making high-speed computers for scientific work. 许多先前不经销计算机的公司随着第二代计算机的出现进入计算机行业,其中今天仍然制造计算机的公司之一是控制数据公司(CDC),他们以制造用于科学工作的高速计算机而著名。20
  • 21. 1.2 Computer Generations 1.2.2 Second-Generation Computers: 1959~1963 Remintong Rand, now called Sperr-Rand Corporation, made several second-generation UNIVAC computers. IBM, however, continued to dominate the industry. One of the most popular second-generation computers was the IBM 1401, which was a medium-sized computer used by many businesses. Remintong Rand,现在叫做Sperr-Rand公司,制造了一些第二代UNIVAC计算机。然而,IBM继续称霸计算机行业。最流行的第二代计算机之一是IBM 1401, 这是一部许多企业使用的中型计算机。 All computers at this time were mainframe computers costing over a million dollars. The first minicomputer became available in 1960 and cost about $120,000. This was the PDP-1, manufactured by Digital Equipment Corporation (DEC). 当时所有的计算机都是价值百万元以上的大型计算机。第一台小型计算机产生于1960年,价值12万美元,它就是由数据设备公司(DEC)制造的PDP-1。 21
  • 22. 1.2 Computer Generations 1.2.2 Second-Generation Computers: 1959~1963 Software also continued to develop during this time. Many new programming languages were designed, including COBOL in 1960. More and more businesses and organizations were beginning to use computers for their data processing needs. 在此期间软件也在继续发展。许多新的编程语言被发明,包括1960年发明的COBOL。越来越多的企业和组织开始使用计算机以满足他们的数据处理需要。 22
  • 23. 1.2 Computer Generations 1.2.3 Third-Generation Computers: 1964~1970 The technical development that marks the third generation of computers is the use of integrated circuits or ICs in computers. An integrated circuit is a piece of silicon (a chip) containing numerous transistors. One IC replaces many transistors in a computer; result in a continuation of the trends begun in the second generation. These trends include reduced size, reduced cost, increased speed, and reduced need for air conditioning. 作为第三代计算机标志的技术发展是在计算机中使用集成电路或简称IC。一个集成电路就是包含许多晶体管的一个硅片(芯片)。一个集成电路代替了计算机中的许多晶体管,导致了始于第二代的一些趋势的继续。这些趋势包括计算机体积减小、成本降低、速度提高和对空调的需要减少。 23
  • 24. 1.2 Computer Generations 1.2.3 Third-Generation Computers: 1964~1970 Although integrated circuits were invented in 1958, the first computers to make extensive use of them were not available until 1964. In that year, IBM introduced a line of mainframe computers called the System/360. The computers in this line became the most widely used third-generation machines. There were many models in the System/360 line, ranging from small, relatively slow, and inexpensive ones, to large, very fast, and costly models. All models, however, were compatible so that programs written for one model could be used on another. This feature of compatibility across many computers in a line was adopted by other manufacturers of third-generation computers. 虽然集成电路发明于1958年,但是直到1964年才出现了第一台广泛使用IC的计算机。那一年,IBM推出了称为System/360的大型计算机系列。这一系列的计算机成为使用最广泛的第三代计算机。在System/360系列中有许多机型, 从小型的、相对较慢的且价格低廉的机型,到大型的、非常快的且价格昂贵的机型。然而,所有的机型都是兼容的,以便在一个机型上编写的程序可以用于另一个机型。这个在许多计算机系列间兼容的特征被其他第三代计算机制造商所采用。 24
  • 25. 1.2.3 Third-Generation Computers: 1964~1970 The third computer generation was also the time when minicomputers became widespread. The most popular model was the PDP-8, manufactured by DEC. Other companies, including Data General Corporation and Hewlett-Packard Company, introduced minicomputers during the third generation. 计算机的第三代也是小型计算机普及的时代。最流行的小型机是由DEC制造的PDP-8。其他公司,包括数据通用公司和惠普(Hewlett-Packard)公司,在第三代期间开发了小型计算机。 1.2 Computer Generations 25
  • 26. 1.2.3 Third-Generation Computers: 1964~1970 The principal software development during the third computer generation was the increased sophistication of operating systems. Although simple operating systems were developed for first-and second-generation computers, many of the features of modern operating systems first appeared during the third generation. These include multiprogramming, virtual memory, and time-sharing. The first operating systems were mainly batch systems, but during the third generation, interactive systems, especially on minicomputers, became common. The BASIC programming language was designed in 1964 and became popular during the third computer generation because of its interactive nature. 在第三代计算机期间,软件的主要发展是操作系统的复杂化程度提高。虽然为第一代和第二代计算机开发了简单的操作系统,许多现代操作系统的特征首先在第三代期间出现。这些特征包括多道程序设计、虚拟存储和分时技术。第一代操作系统主要是批处理系统,但是在第三代期间,交互式系统开始普及,尤其是在小型计算机上。BASIC语言发明于1964年,并由于其交互式特征而在第三代计算机期间大为流行。1.2 Computer Generations 26
  • 27. 1.2.4 Fourth-Generation Computers: 1971~? The fourth generation of computers is more difficult to define than the other three generations. This generation is characterized by more and more transistors being contained on a silicon chip. First there was Large Scale Integration (LSI), with hundreds and thousands of transistors per chip, then came Very Large Scale Integration (VLSI), with tens of thousands and hundreds of thousands of transistors. The trend continues today. 第四代计算机比其他三代更难以定义。这一代计算机的特征是一个芯片上包含越来越多的晶体管。首先,出现了一个芯片上具有数百和数千个晶体管的大规模集成电路(LSI),接着出现了一个芯片上具有数万和数十万个晶体管的超大规模集成电路(VLSI)。这个趋势在今天仍在持续。1.2 Computer Generations 27
  • 28. 1.2.4 Fourth-Generation Computers: 1971~? Although not everyone agrees that there is a fourth computer generation, those that do feel that it began in 1971, when IBM introduced its successors to the System/360 line of computers. These mainframe computers were called the System/370, and current-model IBM computers, although not called System/370s, evolved directly from these computers. 虽然并不是每个人都同意存在一个第四代,那些认为存在的觉得它开始于1971年,其时IBM开发了System/360系列计算机的下一系列产品。这些大型计算机称为System/370,当前的IBM计算机虽然不叫做System/370,但都是从这些计算机直接发展而来的。 Minicomputers also proliferated during the fourth computer generation. The most popular lines were the DEC PDP-11 models and the DEC VAX, both of which are available in various models today. 小型计算机也在第四代期间迅速增长。最流行的系列是DEC公司的PDP-11机和DEC的VAX机,二者在今天的各种机型中仍然有效。 1.2 Computer Generations 28
  • 29. 1.2 Computer Generations 1.2.4 Fourth-Generation Computers: 1971~? Supercomputers first became prominent in the fourth generation. Although many companies, including IBM and CDC, developed high-speed computers for scientific work, it was not until Cray Research, Inc., introduced the Cray 1 in 1975 that supercomputers became significant. Today, supercomputers are an important computer classification. 超级计算机首先在第四代中突起。虽然包括IBM和CDC(控制数据公司)在内的许多公司都为科学工作开发了高速计算机,但是直到1975年Cray研究有限公司推出了Cray 1,超级计算机才变得有意义。今天,超级计算机是重要的计算机分类。 29
  • 30. 1.2 Computer Generations 1.2.4 Fourth-Generation Computers: 1971~? Perhaps the most important trend that began in the fourth generation is the proliferation of microcomputers. As more and more transistors were put on silicon chips, it eventually became possible to put an entire computer processor, called a microprocessor, on a chip. The first computer to use microprocessors became available in the mid-1970s. The first microcomputer designed for personal use was the Altair, which was sold in 1975. The first Apple computer, marketed with the IBM PC in 1981. Today, microcomputers far outnumber all other types of computers combined. 也许在第四代计算机开始的最重要趋势是微型计算机的增长。随着越来越多的晶体管被集成到硅芯片上,将一整个计算机处理器(称为微处理器)放在一个芯片上终于成为可能。使用微处理器的第一部计算机出现于1970年代。第一部专为个人使用设计的微型计算机是Altair,它于1975进入市场。第一部苹果计算机在1981年与IBM个人计算机一起在市场上销售。今天,微型计算机数目远远超过其他所有类型计算机的总和。30
  • 31. 1.2 Computer Generations 1.2.4 Fourth-Generation Computers: 1971~? Software development during the fourth computer generation started off with little change from the third generation. Operating systems were gradually improved, and new languages were designed. Database software became widely used during this time. The most important trend, however, resulted from the microcomputer revolution. Packaged software became widely available for microcomputers so that today most software is purchased, not developed from scratch. 在计算机的第四代期间,软件的发展开始与第三代有所不同。操作系统在逐渐地改进,而新的语言被发明。期间数据库软件被广泛使用。然而,最重要的趋势起因于微型计算机革命。用于微型计算机的软件包随处可得,因此今天大多数的软件可以购得,而不需从头开始开发。 31
  • 32. 1.2.5 Generationless Computers We may have defined our last generation of computers and begun the era of generationless computers. Even though computer manufacturers talk of “fifth” and “sixth”-generation computers, this talk is more a marketing play than a reflection of reality. 我们可能已经定义了我们最新一代计算机而且开始了计算机的无代时代。即使计算机制造商谈到“第五”和“第六”代计算机,这些说法更多是市场行为,而不是真实的反映。 Advocates of the concept of generationless computers say that even though technological innovations are coming in rapid succession, no single innovation is, or will be, significant enough to characterize another generation of computers. 无代计算机的观念提倡者说,即使科技革新接二连三地迅速出现,没有一种革新是,或将是足够重要,作为另一代计算机的特征。1.2 Computer Generations 32
  • 33. New Words & Expressions: glean vt., vi. 搜集(情报或事实) MD abbr. Maryland(马里兰) Tflops abbr. teraflops 每秒兆兆(1012)次 architecture n.体系机构 terabit n.兆兆位 factor n. 阶乘 bandwidth n.带宽 Terabyte n. 兆兆(1012)字节; Petabyte n. 千兆兆(1015)字节 microprocessor n.[计]微处理器 contemplate v.凝视, 沉思 order n. 阶,次 turbulence n. 扰动;湍流 GB=GigaBit,千兆位; = GigaByte,吉字节 flops n. 每秒浮点运算次数(floating-point operation per second) 1.3 Near-future Supercomputer Directions 33
  • 34. Some idea of what might be happening in the near future in supercomputer design can be gleaned from a press release issued by the US Department of Energy (DoE). It came out of the SUPERCOMPUTING 2002 Conference held last November in Baltimore, MD. The press release announced that the DoE had awarded IBM a $290 (USD) million contract to build the two fastest supercomputers in the world with a combined peak speed of 460 TFlops. To get an idea of the speed computing throughput 460 teraflops represents, the press release states that, “These two systems will have more than one-and-a-half times the combined processing power of all 500 machines on the recently announced TOP 500 List of Supercomputers.” 从美国能源部发行的通告中,可以收集一些有关在不久的将来超级计算机设计中可能发生的事情的概念。它来自在马里兰州巴尔的摩市召开的2002年超级计算会议。该通告称能源部已给IBM拨款2.9亿美元建造世界上最快的两部超级计算机,其最高综合速度为每秒460兆兆次。为了理解每秒460兆兆次速度的含义,通告解释说,“这两个系统将会具有最近发布的500强超级计算机的总处理能力的1.5倍还多。”1.3 Near-future Supercomputer Directions 34
  • 35. The first system, “ASCI Purple,” [apparently the DoE likes colorful names] will be the world’s first supercomputer capable of 100 Tflops. ASCI Purple will have a massive cluster of POWER-based IBM eServer systems and IBM storage systems. This supercomputer represents a fifth-generation system under the Advanced Simulation and Computing Initiative (ASCI) Program. It will serve as the primary supercomputer for DoE. 第一个系统“ASCI Purple”,[显然能源部;生动的名字]将会是世界的第一部能够运算每秒100兆兆次的超级计算机。ASCI Purple将具有基于POWER系列的IBM eServer 系统和 IBM 存储系统的宏大组群。这台超级计算机代表模拟和计算行动计划(ASCI)支持的第五代系统。它将作为能源部主要的超级计算机。1.3 Near-future Supercomputer Directions 35
  • 36. 1.3 Near-future Supercomputer Directions According to the press release, the second system will be a research machine called Blue Gene/L. It will employ advanced IBM semiconductor and system technologies based on new architectures being developed by DoE and IBM. Blue Gene/L is expected to achieve a peak performance of 360 TFlops with 130,000 processors running under the Linux operating system. It will have the capability to process data at a rate of one terabit per second, equivalent to the data transmitted by ten thousand weather satellites. Applications are expected to include the simulation of very complex physical phenomena in areas such as turbulence, biology and high explosives. 根据通告,第二个系统将会是一部被称为Blue Gene/L的研究机器,它将使用基于新结构的先进的IBM半导体和系统技术,该新结构是能源部和IBM共同开发的。Blue Gene/L具有13万台处理器,在Linux操作系统下运行,可望达到每秒360兆兆次的性能。它将具有以每秒1兆兆位的速度处理数据的能力,等同于一万个气象卫星传输的数据。其应用预期包括对非常复杂现象的模拟,如湍流、生物学和高空爆炸。 36
  • 37. 1.3 Near-future Supercomputer Directions The ASCI Purple system will use IBM’s next generation microprocessor, the POWER5, employing a total of 12,544 of them. These 12,544 processors will be spread among 196 individual computers. The total memory bandwidth will be 156,000 GBs, the equivalent of simultaneously playing 31,200 DVD movies. A super-fast data highway with a total interconnect bandwidth of 12,500 GB will interconnect the 196 computers. The IBM AIXL operating system will be used to run this configuration. The operating system will contain 50 terabytes of memory, an amount that is 400,000 times the capacity of the average desktop PC. There will also be two petabytes of disk storage or holding the content of approximately one billion books. ASCI Purple系统将使用IBM的下一代微处理器POWER5,总数为12,544个。这12,544个处理器将分布在196部单独的计算机之中。总内存带宽将是15.6GB,等同于同时地播放 31,200部DVD电影。一条具有12,500 GB带宽的超快速数据通道将会把196台计算机互相连接。IBM AIXL 操作系统将用于运行一个配置。该操作系统将包50兆兆字节内存,容量是平均桌面个人计算机的40万倍。还将有2千兆兆字节的磁盘存储,或可容纳大约十亿本书的内容。37
  • 38. 1.3 Near-future Supercomputer Directions Finally, since the UNIVAC-1’s introduction, raw computer speed has increased by about 11 to 12 orders of magnitude in about 50 years, or a factor of 10 every five years. This is a truly remarkable achievement. It’s also interesting to contemplate that, if this growth continues over the next 50 years, then by the 100th anniversary of the UNIVAC-1, computers will be operating at speeds on the order of 1023 Flops! 最后, 自从UNIVAC-1的发明以来,计算机的原始速度在50年内增加了11至12个数量级,或每五年增加10倍。这是一个真正显著的成就。设想一下也很有趣,如果在未来50年间仍以这样的速度持续增长,到UNIVAC-1诞生的100周年,计算机将会以大约每秒1023次的浮点运算速度运行! 38
  • 39. 一、复杂长句多 科技文章要求叙述准确,推理谨严,因此一句话里包含三四个甚至五六个分句的,并非少见。译成汉语时,必须按照汉语习惯破成适当数目的分句,才能条理清楚,避免洋腔洋调。这种复杂长句居科技英语难点之首,要学会运用语法分析方法来加以解剖,以便以短代长,化难为易。例如: Factories will not buy machines unless they believe that the machine will produce goods that they are able to sell to consumers at a price that will cover all cost. 这是由一个主句和四个从句组成的复杂长句,只有进行必要的语法分析,才能正确理解和翻译。现试译如下: 除非相信那些机器造出的产品卖给消费者的价格足够支付所有成本,否则厂家是不会买那些机器的。 节译:要不相信那些机器造出的产品售价够本,厂家是不会买的。 后一句只用了24个字,比前句40个字节约用字40%,而对原句的基本内容无损。可见,只要吃透原文的结构和内涵,翻译时再在汉语上反复推敲提炼,复杂的英语长句,也是容易驾驭的。 科技英语的特点 39
  • 40. 科技英语的特点 二、被动语态多 英语使用被动语态大大多于汉语,如莎士比亚传世名剧《罗密欧与朱丽叶》中的一句就两次用了被动语态: Juliet was torn between desire to keep Romeo near her and fear for his life, should his presence be detected. 朱丽叶精神上受到折磨,既渴望和罗密欧形影不离,又担心罗密欧万一让人发现,难免有性命之忧。 科技英语更是如此,有三分之一以上用被动语态。例如: (a) No work can be done without energy. 译文:没有能量决不能做功。 (b) All business decisions must now be made in the light of the market. 译文:所有企业现在必须根据市场来作出决策。 40
  • 41. 科技英语的特点 三、非谓语动词多 英语每个简单句中,只能用一个谓语动词,如果读到几个动作,就必须选出主要动作当谓语,而将其余动作用非谓语动词形式,才能符合英语语法要求。 非谓语动词有三种:动名词、分词(包括现在分词和过去分词)和不定式。例如: 要成为一个名符其实的内行,需要学到老。 这句中,有“成为”、“需要”和“学”三个表示动作的词,译成英语后为: To be a true professional requires lifelong learning. 可以看出,选好“需要”(require)作为谓语,其余两个动作:“成为”用不定式形式 to be,而“学”用动名词形式learning,这样才能符合英语语法要求。 41
  • 42. 科技英语的特点 四、词性转换多 英语单词有不少是多性词,即既是名词,又可用作动词、形容词、介词或副词,字形无殊,功能各异,含义也各不相同,如不仔细观察,必致谬误。例如, light 名词: (启发)in (the)light of由于,根据; (光)high light(s) 强光,精华;(灯)safety light 安全指示灯 形容词:(轻)light industry 轻工业; (明亮)light room 明亮的房间; (淡)light blue 淡蓝色; (薄)light coating 薄涂层 动词: (点燃)light up the lamp 点灯 副词: (轻快)travel light 轻装旅行 (容易)light come, light go 来得容易去得快 诸如此类的词性转换,在科技英语中屡见不鲜,几乎每个技术名词都可转换为同义的形容词。词性转换增加了英语的灵活性和表现力,读者必须从上下文判明用词在句中是何种词性,而且含义如何,才能对全句得到正确无误的理解。42
  • 43. Computer English Chapter 2 Organization of Computers
  • 44. Key points: useful terms and organization of computers Difficult points: describing the organization of computers44
  • 45. Requirements:1. Terms of computer hardware 2. Organization of computers and their functions3. 掌握专业词汇的构成规律,特别是常用词缀及复合词的构成 45
  • 46. New Words & Expressions: instruction cycle 指令周期 decode vt.解码, 译解 bus n. 总线 pins n.插脚, 管脚 uppermost adj.最高的;adv.在最上 address bus 地址总线 data bus 数据总线 via prep.经, 通过, 经由 multibit 多位 bidirectional 双向的 unidirectional 单向的 hierarchy n.层次,层级 microprocessor n.微处理器 register n.寄存器 timing n.定时;时序;时间选择 synchronize vt.使...同步 assert vt.主张,发出 deassert vt. 撤销 trigger vt.引发, 引起, 触发 map v.映射 port n.端口2.1 Basic Organization of Computers Abbreviations: CPU(Central Processing Unit) 中央处理器 I/O(Input/Output) 输入输出(设备)46
  • 47. 2.1 Basic Organization of ComputersFig.2-1 Generic computer organization47
  • 48. 2.1 Basic Organization of ComputersMost computer systems, from the embedded controllers found in automobiles and consumer appliances to personal computers and mainframes, have the same basic organization. This organization has three main components: the CPU, the memory subsystem, and the I/O subsystem. The generic organization of these components is shown in Figure 2-1.大多数计算机系统,从汽车和日用电器中的嵌入式控制器到个人计算机和大型主机,都具有相同的基本组成。其基本组成包括三个主要部件:CPU、存储器子系统和I/O子系统。这些部件的一般组成如图2-1所示。48
  • 49. Physically, a bus is a set of wires. The components of the computer are connected to the buses. To send information from one component to another, the source component outputs data onto the bus. The destination component then inputs this data from the bus. As the complexity of a computer system increases, it becomes more efficient (in terms of minimizing connections) at using buses rather than direct connections between every pair of devices. Buses use less space on a circuit board and require less power than a large number of direct connections. They also require fewer pins on the chip or chips that comprise the CPU.2.1.1 System Buses从物理上来说,总线就是一组导线。计算机的部件就是连在总线上的。为了将信息从一个部件传到另一个部件,源部件先将数据输出到总线上,然后目标部件再从总线上接受这些数据。随着计算机系统复杂性的不断增长,使用总线比每个设备对之间直接连接要有效得多(就减少连接数量而言)。与大量的直接连接相比,总线使用较少的电路板空间,耗能更少,并且在芯片或组成CPU的芯片组上需要较少的引脚。49
  • 50. The system shown in Figure 2-1 has three buses. The uppermost bus in this figure is the address bus. When the CPU reads data or instructions from or writes data to memory, it must specify the address of the memory location it wishes to access. It outputs this address to the address bus; memory inputs this address from the address bus and use it to access the proper memory location. Each I/O devices, such as a keyboard, monitor, or disk drive, has a unique address as well. When accessing an I/O device, the CPU places the address of the device on the address bus. Each device can read the address off of the bus and determine whether it is the device being accessed by the CPU. Unlike the other buses, the address bus always receives data from the CPU; the CPU never reads the address bus.图2-1所示的系统包括三组总线。最上面的是地址总线。当CPU从存储器读取数据或指令,或写数据到存储器时,它必须指明将要访问的存储器单元地址。CPU将地址输出到地址总线上,而存储器从地址总线上读取地址,并且用它来访问正确的存储单元。每个I/O设备,比如键盘、显示器或者磁盘,同样都有一个唯一的地址。当访问某个I/O设备时,CPU将此设备的地址放到地址总线上。每一个设备均从总线上读取地址并且判断自己是否就是CPU正要访问的设备。与其他总线不同,地址总线总是从CPU上接收信息,而CPU从不读取地址总线。2.1.1 System Buses50
  • 51. Data is transferred via the data bus. When the CPU fetches data from memory, it first outputs the memory address on its address bus. Then memory outputs the data onto the data bus; the CPU can then read the data from the data bus. When writing data to memory, the CPU first outputs the address onto the address bus, then outputs the data onto the data bus. Memory then reads and stores the data at the proper location. The processes for reading data from and writing data to the I/O devices are similar.数据是通过数据总线传送的。当CPU从存储器中取数据时,它首先把存储器地址输出到地址总线上,然后存储器将数据输出到数据总线上,这样CPU就可以从数据总线上读取数据了。当CPU向存储器中写数据时,它首先将地址输出到地址总线上,然后把数据输出到数据总线上,这样存储器就可以从数据总线上读取数据并将它存储到正确的单元中。对I/O设备读写数据的过程与此类似。2.1.1 System Buses51
  • 52. The control bus is different from the other two buses. The address bus consists of n lines, which combine to transmit one n-bit address value. Similarly, the lines of the data bus work together to transmit a single multibit value. In contrast, the control bus is a collection of individual control signals. These signals indicate whether data is to be read into or written out of the CPU, whether the CPU is accessing memory or an I/O device, and whether the I/O device or memory is ready to transfer data. Although this bus is shown as bidirectional in Figure 2-1, it is really a collection of (mostly) unidirectional signals. Most of these signals are output from the CPU to the memory and I/O subsystems, although a few are output by these subsystems to the CPU. We examine these signals in more detail when we look at the instruction cycle and the subsystem interface.控制总线与以上两种总线都不相同。地址总线由n根线构成,n根线联合传送一个n位的地址值。类似地,数据总线的各条线合起来传输一个单独的多位值。相反,控制总线是单根控制信号的集合。这些信号用来指示数据是要读入CPU还是要从CPU写出,CPU是要访问存储器还是要访问I/O设备,是I/O设备还是存储器已就绪要传送数据等等。虽然图2-1所示的控制总线看起来是双向的,但它实际上(主要)是单向(大多数都是)信号的集合。大多数信号是从CPU输出到存储器与I/O子系统的,只有少数是从这些子系统输出到CPU的。在介绍指令周期和子系统接口时,我们将详细地讨论这些信号。2.1.1 System Buses52
  • 53. A system may have a hierarchy of buses. For example, it may use its address, data, and control buses to access memory, and an I/O controller. The I/O controller, in turn, may access all I/O devices using a second bus, often called an I/O bus or a local bus. 一个系统可能具有分层次的总线。例如,它可能使用地址、数据和控制总线来访问存储器和I/O控制器。I/O控制器可能依次使用第二级总线来访问所有的I/O设备,第二级总线通常称为I/O总线或者局部总线。2.1.1 System Buses53
  • 54. The instruction cycle is the procedure a microprocessor goes through to process an instruction. First the microprocessor fetches, or reads, the instruction from memory. Then it decodes the instruction, determining which instruction it has fetched. Finally, it performs the operations necessary to execute the instruction. (Some people also include an additional element in the instruction cycle to store results. Here, we include that operation as part of the execute function.) Each of these functions--fetch, decode, and execute--consists of a sequence of one or more operations.指令周期是微处理器完成一条指令处理的步骤。首先,微处理器从存储器读取指令,然后将指令译码,辩明它取的是哪一条指令。最后,它完成必要的操作来执行指令(有人认为在指令周期中还要包括一个附加的步骤来存储结果,这里我们把该操作当作执行功能的一部分)。每一个功能——读取、译码和执行都包括一个或多个操作。 2.1.2 Instruction Cycle54
  • 55. Let's start where the computer starts, with the microprocessor fetching the instruction from memory. First, the microprocessor places the address of the instruction on to the address bus. The memory subsystem inputs this address and decodes it to access the sired memory location. (We look at how this decoding occurs when we examine the memory subsystem in more detail later in this chapter.)我们从微处理器从存储器中取指令开始讲述。首先,微处理器把指令的地址放到地址总线上,然后,存储器子系统从总线上输入该地址并予以译码,去访问指定的存储单元。(译码是如何进行的,我们将在后面的章节中介绍存储器子系统是更为详细的讨论。) 2.1.2 Instruction Cycle55
  • 56. After the microprocessor allows sufficient time for memory to decode the address and access the requested memory location, the microprocessor asserts a READ control signal. The READ signal is a signal on the control bus which the microprocessor asserts when it is ready to read data from memory or an I/O device. (Some processors have a different name for this signal, but all microprocessors have a signal to perform this function.) Depending on the microprocessor, the READ signal may be active high (asserted - 1) or active low (asserted - 0).当微处理器为存储器留出充足的时间来对地址译码和访问所需的存储单元之后,微处理器发出一个读(READ)控制信号。当微处理器准备好可以从存储器或是I/O设备读数据时,它就在控制总线上发一个读信号。(一些处理器对于这个信号有不同的名字,但所有处理器都有这样的信号来执行这个功能。)根据微处理器的不同,读信号可能是高电平有效(信号=1),也可能是低电平有效(信号=0)。 2.1.2 Instruction Cycle56
  • 57. When the READ signal is asserted, the memory subsystem places the instruction code to be fetched onto the computer system's data bus, The microprocessor then inputs this data from the bus and stores it in one of its internal registers. At this point, the microprocessor has fetched the instruction.读信号发出后,存储器子系统就把要取的指令码放到计算机的数据总线上,微处理器就从数据总线上输入该数据并且将它存储在其内部的某个寄存器中。至此,微处理器已经取得了指令。2.1.2 Instruction Cycle57
  • 58. Next, the microprocessor decodes the instruction. Each instruction may require a different sequence of operations to execute the instruction. When the microprocessor decodes the instruction, it determines which instruction it is in order to select the correct sequence of operations to perform. This is done entirely within the microprocessor; it does not use the system buses.接下来,微处理器对这条指令译码。每一条指令可能要有不同的操作序列来执行。当微处理器对该指令译码是,它确定处理的是哪一条指令以便选择正确的操作序列去执行。这一步完全在微处理器内完成,不需要使用系统总线。 2.1.2 Instruction Cycle58
  • 59. Finally, the microprocessor executes the instruction. The sequence of operations to execute the instruction varies from instruction to instruction. The execute routine may read data from memory, write data to memory, read data from or write data to an I/O device, perform only operations within the CPU, or perform some combination of these operations. We now look at how the computer performs these operations from a system perspective.最后,微处理器执行该指令。指令不同,执行的操作序列也不同。执行过程可以是从存储器读取数据,写数据到存储器,读或写数据到I/O设备,执行CPU内部操作或者执行多个上述操作的组合。下面我们从系统的角度来看计算机是怎样执行这些操作的。 2.1.2 Instruction Cycle59
  • 60. To read data from memory, the microprocessor performs the same sequence of operations it uses to fetch an instruction from memory. After all, fetching an instruction is simply reading it from memory. Figure 2-2(a) shows the timing of the operations to read data from memory.微处理器从存储器读取数据所执行的操作序列,同从存储器中去一条指令是一样的。毕竟取指令就是简单地从存储器中读取它。图2-2(a)显示了从存储器中读取数据的操作时序。 2.1.2 Instruction Cycle60
  • 61. In Figure 2-2, notice the top symbol, CLK. This is the computer system clock; the microprocessor uses the system clock to synchronize its operations. The microprocessor places the address onto the bus at the beginning of a clock cycle, a 0/1 sequence of the system clock. One clock cycle later, to allow time for memory to decode the address and access its data, the microprocessor asserts the READ Signal. This causes memory to place its data onto the system data bus. During this clock cycle, the microprocessor reads the data off the system bus and stores it in one of its registers. At the end of the clock cycle it removes the address from the address bus and deasserts the READ signal. Memory then removes the data from the data bus, completing the memory read operation.在图2-2中,注意最上面的符号CLK,它是计算机的系统时钟,微处理器用系统时钟使其操作同步。在一个时钟周期(系统时钟的0/1序列)的开始位置,微处理器将地址放到总线上。一个时钟周期(允许存储器对地址译码和访问数据的时间)之后,微处理器才发出读信号。这使得存储器将数据放到数据总线上。在这个时钟周期之内,微处理器从系统总线上读取数据,并存储到它的某个寄存器中。在这个时钟周期结束时,微处理器撤消地址总线上的地址,并撤消读信号。然后存储器从数据总线上撤消数据,也就完成了存储器的读操作。2.1.2 Instruction Cycle61
  • 62. The timing of the memory write operation is shown in Figure 2-2(b). The processor places the address and data onto the system buses during the first clock cycle. The microprocessor then asserts a WRITE control signal (or its equivalent) at the start of the second clock cycle. Just as the READ signal causes memory to read data, the WRITE signal triggers memory to store data. Some time during this cycle, memory writes the data on the data bus to the memory location whose address is on the address bus. At the end of this cycle, the processor completes the memory write operation by removing the address and data from the system buses and deasserting the WRITE signal.存储器写操作的时序如图2-2(b)所示。在第一个时钟周期,处理器将地址和数据放到总线上,然后在第二个时钟周期开始 时发出一个写(WRITE)控制信号(或与之等价的信号)。像读信号促使存储器读取数据一样,写信号促使存储器存储数据。在这个时钟周期的某个时刻,存储器将数据总线上的数据写入地址总线指示的存储单元内。当这个时钟周期结束,微处理器从系统总线上撤消地址、数据及写信号后,就完成了存储器的写操作。 2.1.2 Instruction Cycle62
  • 63. The I/O read and write operations are similar to the memory read and write operations. A processor may use either memory mapped I/O or isolated I/O. If the processor supports memory mapped I/O, it follows the same sequences of operations to input or output data as to read data from or write data to memory, the sequences shown in Figure 2-2. (Remember, in memory mapped I/O, the processor treats an I/O port as a memory location, so it is reasonable to treat an I/O data access the same as a memory access.) Processors that use isolated I/O follow the same process but have a second control signal to distinguish between I/O and memory accesses. (CPUs that use isolated I/O can have a memory location and an I/O port with the same address, which makes this extra signal necessary.) I/O的读写操作与存储器的读写操作类似。处理器可以使用存储器影射I/O或者是单独I/O。如果处理器支持存储器影射I/O,则它遵循从存储器读写数据同样的操作顺序,该顺序如图2-2所示(记住,在存储器影射I/O中,处理器把一个I/O端口当作某个存储单元,当然I/O的数据访问同存储器的数据访问一样的)。使用单独I/O的处理器遵循同样的处理过程,但是另有一个控制信号用以区别是I/O访问还是存储器访问(使用单独I/O的CPU允许一个存储单元和某个I/O端口具有相同的地址,因此需要这一额外的信号加以区分)。 2.1.2 Instruction Cycle63
  • 64. Finally, consider instructions that are executed entirely within the microprocessor. The INAC instruction of the Relatively Simple CPU, and the MOV r1, r2 instruction of the 8085 microprocessor, can be executed without accessing memory or I/O devices. As with instruction decoding, the execution of these instructions does not make use of the system buses.最后,考虑一下完全在微处理器内部执行的指令。相对简单CPU的INAC指令和8085的MOV r1,r2指令的执行都不要访问存储器和I/O设备。按照指令译码的结果,这些指令的执行不会用到系统总线。 2.1.2 Instruction Cycle64
  • 65. New Words & Expressions: latch v.闭锁,锁存 program counter 程序计数器 instruction register 指令寄存器 operand n. 操作数 increment n.增量,加1 flag register 标志寄存器 pipeline n.流水线 microsequenced 微层序的 local bus 局部总线 Abbreviations: ALU (Arithmetic Logic Unit) 算术逻辑单元 2.2 CPU ORGANIZATION65
  • 66. The CPU controls the computer. It fetches instructions from memory, supplying the address and control signals needed by memory to access its data. The CPU decodes the instruction and controls the execution procedure. It performs some operations internally, and supplies the address, data, and control signals needed by memory and I/O devices to execute the instruction. Nothing happens in the computer unless the CPU causes it to happen. CPU控制整个计算机。它从存储器中取指令,提供存储器需要的地址和控制信号。CPU对指令译码并且控制整个执行过程。它执行一些内部操作,并且为存储器和I/O设备执行指令提供必要的地址、数据和控制信号。除非CPU激发,否则,计算机什么事情都不会发生。 2.2 CPU ORGANIZATION66
  • 67. Internally, the CPU has three sections, as shown in Figure 2-3. The register sections, as its name implies, includes a set of registers and a bus or other communication mechanism. The registers in a processor's instruction set architecture are found in this section of the CPU. The system address and data buses interact with this section of the CPU. The register section also contains other registers that are not directly accessible by the programmer. The relatively simple CPU includes registers to latch the address being accessed in memory and a temporary storage register, as well as other registers that are not a part of its instruction set architecture.CPU内部有三大分区,如图2-3所示。寄存器区,顾名思义,它包括一组寄存器、一条总线或其他通信机制。微处理器指令集结构中的寄存器就属于CPU的这一分区。系统的地址和数据总线与寄存器交互。此分区还包括程序员不能直接访问的一些寄存器。相对简单CPU含有寄存器用以锁存正在访问的存储器地址,还有暂存器以及指令集结构中没有的其他寄存器等。 2.2 CPU ORGANIZATION67
  • 68. During the fetch portion of the instruction cycle, the processor first outputs the address of the instruction onto the address bus. The processor has a register called the program counter; the CPU keeps the address of the next instruction to be fetched in this register. Before the CPU outputs the address onto the system's address bus, it retrieves the address from the program counter register. At the end of the instruction fetch, the CPU reads the instruction code from the system data bus. It stores this value in an internal register, usually called the instruction register or something similar.在指令周期的取指阶段,处理器首先将指令的地址输出到地址总线上。处理器有一个寄存器叫做程序计数器,CPU将下一条要取的指令的地址存放在程序计数器中。在CPU将地址输出到系统的地址总线之前,必须从程序计数器中取出该地址。在指令结束前,CPU从系统时局总线上读取指令码,它把该指令码存储在某个内部寄存器中,该寄存器通常称作指令寄存器或其他相似的名字。 2.2 CPU ORGANIZATION68
  • 69. The arithmetic logic unit or ALU performs most arithmetic and logical operations, such as adding or ADDing values. It receives its operands from the register section of the CPU and stores its results back in the register section. Since the ALU must complete its operations within a single clock cycle, it is constructed using only combinatorial logic. The ADD instructions in the relatively simple CPU and the 8085 microprocessor use the ALU during their executions.算术逻辑单元执行大部分的算术逻辑运算,如加法、逻辑与等运算。它从CPU的寄存器取得操作数,然后将运算结果再存回到寄存器区。由于必须在一个时钟周期内完成操作,因此ALU只采用组合逻辑构造而成。相对简单CPU和8085微处理器中的ADD指令在执行中都有使用ALU。 2.2 CPU ORGANIZATION69
  • 70. Just as the CPU controls the computer (in addition to its other functions), the control unit controls the CPU. This unit generates the internal control signals that cause registers to load data, increment or clear their contents, and output their contents, as well as cause the ALU to perform the correct function. These signals are shown as control signals in Figure 2-3. The control unit receives some data values from the register unit, which it uses to generate the control signals. This data includes the instruction code and the values of some flag registers. 同CPU控制整个计算机(除了其他功能外)一样,控制单元控制着CPU。这个单元产生内部控制信号,促使寄存器装载数据,自动加1或清零,输出它的内容,使得ALU完成正确的操作等等。这些信号作为控制信号显示在图2-3中。控制单元从寄存器区取得一些数据用以产生控制信号,这些数据包括指令码和某些标志寄存器的值。 2.2 CPU ORGANIZATION70
  • 71. The control unit also generates the signals for the system control bus, such as the READ, WRITE, and signals. A microprocessor typically performs a sequence of operations to fetch, decode, and execute an instruction. By asserting these internal and external control signals in the proper sequence, the control unit causes the CPU and the rest of the computer to perform the operations needed to correctly process instructions. 2.2 CPU ORGANIZATION控制单元也产生系统控制总线上的信号,例如READ,WRATE, 信号等。典型的一个微处理器执行取指令、译指令和执行指令等一系列的操作。通过以正确的顺序激发这些内部或外部控制信号,控制单元使CPU和计算机的其余部分完成正确处理指令所需要的操作。71
  • 72. This description of the CPU is incomplete. Current processors have more complex features that improve their performance. One such mechanism, the instruction pipeline, allows the CPU to fetch one instruction while simultaneously executing another instruction. 2.2 CPU ORGANIZATION以上对CPU的描述并不完整。现在的处理器拥有更加复杂的特征以提高其性能。这些机制中有一种是指令流水线技术,它允许CPU在执行一条指令的同时取出另一条指令。72
  • 73. In this section we have introduced the CPU from a system perspective, but we have not discussed its internal design. We examine the registers, data paths, and control unit, all of which act together to cause the CPU to properly fetch, decode, and execute instructions. Microsequenced CPUs have the same registers, ALUs and data paths as hardwired CPUs, but completely different control units. 本节我们从系统的角度介绍了CPU,但我们还没有讨论它的内部设计。我们描述了CPU的寄存器、数据通路、控制单元等,所有部件一起工作使CPU正确地读取、译码和执行指令。微层序CPU具有同硬连线CPU一样的寄存器、ALU和数据通路,但二者控制单元完全不同。 2.2 CPU ORGANIZATION73
  • 74. 2.3 Memory Subsystem Organization and InterfacingNew Words & Expressions: multibyte n.多字节 MB n.兆字节 shut off n.切断,关闭 enable n..使能 tri-state 三态 tri-stated 高阻态 dimension n.尺度, 维(数) configuration n.构造, 结构, 配置 as far as 尽;就;至于 high-order 高位 low-order 低位 interleaving n.交叉,交错 contiguous adj.邻近的, 接近的 assign vt.分配, 指派 big endian 高位优先 little endian 低位优先 hexadecimal adj.十六进制的;n.十六进制 alignment n.对齐方式 leftmost adj.最左边的 rightmost adj.最右边的,最右面的 consecutive adj.连续的, 联贯的 cache n.高速缓冲 virtual memory 虚拟存储器 buffer n.缓冲器 ROM(Read Only Memory) 只读存储器 RAM(Random Access Memory) 随机存取存贮器 RISC(Reduced Instruction Set Computer) 精简指令集计算机74
  • 75. 2.3 Memory Subsystem Organization and InterfacingIn this section we examine the construction and functions of the memory subsystem of a computer. We review the different types of physical memory and the internal organization of their chips. We discuss the construction of the memory subsystem, as well as multibyte word organizations and advanced memory organizations.本节我们将讨论计算机中存储器子系统的结构和功能。我们将会回顾不同类型的物理存储器及其芯片的内部组成,讨论存储器子系统的结构,以及多字节的组织和高级存储器的组成。75
  • 76. 2.3.1 Types of MemoryThe internal organizations of ROM and RAM chips are similar. To illustrate the simplest organization, a linear organization, consider an 82 ROM chip. For simplicity, programming components are not shown. This chip has three address inputs and two data outputs, and 16 bits of internal storage arranged as eight 2-bit locations.存储器芯片有两种类型:只读存储器(ROM)和随机存取存储器(RAM)。只读存储器芯片是为数据(此数据可包括程序的指令)只读的应用而设计的。这些芯片在加入系统之前,就已经被某个外部编程器而装好数据了。这个工作一旦完成,其数据通常不再改变。ROM芯片总是保存有数据,甚至在芯片断电以后。例如,一个微波炉的嵌入式控制器可以连续运行一个不变的程序。这个程序就存储在一片ROM上。76
  • 77. Random Access Memory (RAM), also called read/write memory, can be used to store data that changes. This is the type of memory referred to as X MB of memory in ads for PCs. Unlike ROM, RAM chips lose their data once power is shut off. Many computer systems, including personal computers, include both ROM and RAM.2.3.1 Types of Memory随机访问存储器也称为读写存储器,用来存储可以改变的数据。这就是我们在个人电脑广告上经常看到的XX MB的内存所指的那种类型。不像ROM,RAM芯片一旦掉电,数据就会丢失。许多计算机系统,包括个人电脑,都同时拥有ROM和RAM。77
  • 78. 2.3.2 Internal Chip OrganizationThe internal organizations of ROM and RAM chips are similar. To illustrate the simplest organization, a linear organization, consider an 82 ROM chip. For simplicity, programming components are not shown. This chip has three address inputs and two data outputs, and 16 bits of internal storage arranged as eight 2-bit locations.ROM和RAM芯片的内部组成是相似的。为了说明一个最简单的组成——线性组成,我们来考虑一个82的ROM芯片。为了简化,编成器件没有画出来。这个芯片有三个地址输入端和两个数据输出端,以及16位的内部存储元件,它排列成8个单元,每个单元2位。78
  • 79. The three address bits are decoded to select one of the eight locations, but only if the chip enable is active. If CE=0, the decoder is disabled and no location is selected. The tri-state buffers for that location's cells are enabled, allowing data to pass to the output buffers. If both CE and OE set to 1, these buffers are enabled and the data is output from the chip; otherwise the outputs are tri-stated.2.3.2 Internal Chip Organization三个地址位经过译码,可以选择8个中的一个,但只有芯片的使能端要有效才行。如果CE=0,译码器被禁止,则不选择任何单元。该单元上的三态缓冲器是有效的,允许数据输出到缓冲器中。如果CE=1且OE=1,则这些缓冲器有效,数据从芯片中输出;否则,输出是高阻态。79
  • 80. As the number of locations increases, the size of the address decoder needed in a linear organization becomes prohibitively large. To remedy this problem, the memory chip can be designed using multiple dimensions of decoding. 2.3.2 Internal Chip Organization随着单元数量的增加,线性组成中地址译码器的规模变得相当大。为了补救这一问题,存储器芯片可以设计成使用多维译码方式。80
  • 81. In larger memory chips, this savings can be significant. Consider a 40961 chip. The linear organization will require a 12 to 4096 decoder, the size of which is proportional to the number of outputs. (The size of an n to 2n decoder is thus said to be O(2n).) If the chip is organized as a 6464 two dimensional array instead, it will have two 6 to 64 decoders: one to select one of the 64 rows and the other to select one of the 64 cells within the row. The size of the decoders is proportional to 264, or O(22n/2) = O(2n/2 +1). For this chip, the two decoders together are about 3 percent of the size of the one larger decoder.2.3.2 Internal Chip Organization在大型存储器芯片中,这种节省显得至关重要。考虑一个40961芯片,其线性组成将需要一个12—4096译码器,译码器大小与输出的数量成正比(假定一个n—2n译码器的大小是O(2n))。如果芯片排列成6464的二维数组,它将有两个6—64译码器:一个用来选择64行中的一行,另一个用来在选定行中选择64个单元中的一个单元,该译码器的大小正比于264,或写成O(22n/2)=O(2n/2+1)。对于这个芯片,两个译码器总的大小约是那个大译码器大小的3%。 81
  • 82. 2.3.3 Memory Subsystem ConfigurationIt is very easy to set up a memory system that consists of a single chip. We simply connect the address, data, and control signals from their system buses and the job is done. However, most memory systems require more than one chip. Following are some methods for combining memory chips to form a memory subsystem.构造包含一个简单芯片的存储器是非常容易的,我们只需要简单地从系统总线上连接地址信号线、数据信号线和控制信号线就完成了。然而。大多数的存储器系统需要多个芯片,下面是通过存储器芯片组合来形成存储器子系统的一些方法。82
  • 83. 2.3.3 Memory Subsystem ConfigurationTwo or more chips can be combined to create memory with more bits per location. This is done by connecting the corresponding address and control signals of the chips, and connecting their data pins to different bits of the data bus. For example, two 82 chips can be combined to create an 84 memory, as shown in Figure 2-4. Both chips receive the same three address inputs from the bus, as well as the same chip enable and output enable signals. (For now it is only important to know that the signals are the same for both chips; we show the logic to generate these signals shortly.) The data pins of the first chip are connected to bits 3 and 2 of the data bus, and those of the other chip are connected to bits 1 and 0. 两个或多个芯片可以组合起来构造一个每单元有多位的存储器。这可以通过连接芯片相应的地址信号线和控制信号线,并将它们的数据引脚连到数据总线的不同位上来完成。例如,2个82芯片可以组合产生一个84存储器,如图2-4所示。两个芯片从总线上接收相同的三位地址输入,还有共同的芯片使能信号和输出使能信号(目前,我们只要了解两个芯片使用的是同一信号就可以了,稍后我们将说明产生这些信号的逻辑)。第一个芯片的数据引脚连到数据总线的第3位和第2位,第二个芯片的数据引脚则连在第1位和第0位。83
  • 84. 2.3.3 Memory Subsystem ConfigurationWhen the CPU reads data, it places the address on the address bus. Both chips read in address bits A2, A1, and A0 and perform their internal decoding. If the CE and OE signals are activated, the chips output their data onto the four bits of the data bus. Since the address and enable signals are the same for both chips, either both chips or neither chip is active at any given time. The computer never has only one of the two active. For this reason, they act just as a single 84 chip, at least as far as the CPU is concerned.当CPU读取数据时,它将地址放在地址总线上。两个芯片读取地址位A2、A1、A0,并执行内部译码操作。如果CE和OE信号是有效的,两个芯片则输出数据到数据总线的四位上。因为两个芯片的地址和使能信号是相同的,因此在任一时刻两个芯片要么同时有效,要么同时无效。正因如此,它们的行为就像一个单一的84芯片,至少就CPU而言是这样的。84
  • 85. 2.3.3 Memory Subsystem ConfigurationInstead of creating wider words, chips can be combined to create more words. The same two 8 2 chips could instead be configured as a 162 memory subsystem. This is illustrated in Figure 2-5(a). The upper chip is configured as memory locations 0 to 7 (0000 to 0111) and the lower chip as locations 8 to 15 (1000 to 1111). The upper chip always has A3 = 0 and the lower chip has A3=1. This difference is used to select one of the two chips. When A3 =0, the upper chip is enabled and the lower chip is disabled; when A3 = 1, the opposite occurs. (As shown in the figure, other conditions must also occur or neither chip will be selected.) The output enables can be connected, since only the chip that is enabled will output data. Since both chips correspond to the same data bits, both are connected to D1 and D0 of the data bus.除了构造更宽的字以外,芯片组合还可以构造出更多的字。两样的两个82芯片能够组成一个162存储子系统。如图2-5所示。上面的芯片构成存储器的0到7(0000到0111)单元,下面的芯片作为单元8到15(1000到1111)。上面的芯片总是设置A3=0,而下面的芯片A3=1。通过这一区别来选择芯片,当A3=0时,上面的芯片有效,而下面的芯片无效;当A3=1时,情况刚好相反。(如图所示。另一种情况必定会发生,否则没有芯片被选中。)输出使能端需要连接起来,因为只有芯片有效才可以输出数据。由于两个芯片对应相同的数据位,因此都可以连接到数据总线的D1和D0位上。85
  • 86. 2.3.3 Memory Subsystem ConfigurationThis configuration uses high-order interleaving. All memory locations within a chip are contiguous within system memory. However, this does not have to be the case. Consider the configuration shown in Figure 2-5(b), which uses low-order interleaving. The upper chip is enabled when A0=0, or by addresses XXX0, in this case 0, 2, 4, 6, 8, 10, 12, and 14. The lower chip is enabled when A0=1, which is true for addresses l, 3, 5, 7, 9, 11, 13, and 15. Both look the same to the CPU, but low-order interleaving can offer some speed advantages for pipelined memory access, and for CPUs that can read data from more than one memory location simultaneously.这种配置使用的是高位交叉技术。同一芯片的所有存储单元在系统内存中是连续的。然而,不一定非得如此。考虑如图2-5(b)所示的情况,它用的是低位交叉技术。上面的芯片当A0=0或者当地址位为XXX0时有效,此时,地址为0、2、4、6、8、10和12;下面的芯片当A0=1时有效,条件是地址为1、3、5、7、9、11、13和15。对CPU而言,两者是相同的。但低位交叉能为流水线存储器访问提供速度上的优势,对于能够同时从多于一个存储器单元中读取数据的CPU来说,低位交叉也存在速度上的优势。 86
  • 87. 2.3.3 Memory Subsystem ConfigurationThe next step in these designs is to develop the CE and OE input logic. Of these, the output enable is more straightforward. The CPU generally outputs a control signal called RD or RD', or something similar, which it sets active when it wants to read data from memory. This signal is sufficient to drive OE; the logic to drive CE ensures that only the correct chip outputs data. 设计的下一步就是指制定CE和OE的输入逻辑。输出使能更直接一些,CPU通常输出一个控制信号,称作RD或RD'或别的什么,当它想要从主存读取数据时就将其设为有效,用此信号驱动OE就足够了,而驱动CE的逻辑务必确保只有正确的芯片方可输出数据。87
  • 88. 2.3.3 Memory Subsystem ConfigurationThe chip enable signal makes use of the unused address bits. To illustrate, assume that the 8 4 memory of Figure 2-4 is used in a system with 6-bit address bus. Furthermore, assume this chip corresponds to locations 0 to 7 (00 0000 to 00 0111). Address bits A2, A1, and A0 select a location within the memory chips; bits A5, A4, and A3 must be 000 for the chips to be active. 芯片使能信号可利用未使用的地址位。为了说明这一点,假设图2-4中的84存储器被用到一个6位地址总线的系统中,而且,进一步假设这个芯片对应的单元为0到7(00 000到00 0111)。则地址位A2、A1和A0可以用于选中存储芯片中的某个单元,而A5、A4和A3在芯片有效时一定要是000。88
  • 89. 2.3.4 Multibyte Data Organization Many data formats use more than one 8-bit byte to represent a value, whether it is an integer, floating point number, or character string. Most CPUs assign addresses to 8-bit memory locations, so these values must be stored in more than one location. It is necessary for every CPU to define the order it expects for the data in these locations.许多数据格式使用多个字节(一个字节8位)来表示一个数据,而不管此数值是整型数、浮点数还是字符串。由于大多数CPU给8位的存储器单元分配地址,因此这些值必须存储在多个单元中,每个CPU必须定义数据在这些单元中的顺序。89
  • 90. 2.3.4 Multibyte Data Organization There are two commonly used organizations for multibyte data: big endian and little endian. In big endian format, the most significant byte of a value is stored in location X, the following byte in location X+l, and so on. For example, the hexadecimal value 0102 0304H (H for hexadecimal) would be stored, starting in location 100H, as shown in Table 2-1(a).有两种常用的多字节数据排列顺序:高位优先和低位优先。依照高位优先格式,一个数值的最高字节存储在单元X中,次高字节存储在单元X+1中,依次类推。例如,十六进制数01020304H(H表示十六进制)从单元100h开始存储,则存储结果如表2-1(a)所示。90
  • 91. 2.3.4 Multibyte Data Organization In little endian, the order is reversed. The least significant byte is stored in location X, the next byte in location X+1, and so on. The same value, in little endian format, is shown in Table 2-1(b). 依照低位优先格式,顺序正好相反。最低字节存储在单元X中,次字节存储在单元X+1中,依次类推。上例中的同一值,以低位优先格式存储,如表2-1(b)所示。91
  • 92. 2.3.4 Multibyte Data Organization The same organizations can be used for bits within a byte. In big endian organization, bit 0 is the rightmost bit of a byte: the left most bit is bit 7. In little endian organization, the leftmost bit is bit 0 and bit 7 is the rightmost bit.同样的组织方式可用于一个字节中的不同位上。在高位优先结构中,位0代表字节中最右边的位,最左边的位是第7位。在低位优先结构中,最左边的位是0,最右边的位是7。 92
  • 93. 2.3.4 Multibyte Data Organization Which endian organization is used for bytes and words does not impact the performance of the CPU and computer system. As long as the CPU is designed to handle a specific format, neither is better than the other. The main problem comes in transferring data between computers with different endian organizations. For example, if a computer with little endian organization transfers the value 0102 0304H to a computer with big endian organization without converting the data, the big endian computer will read the value as 0403 0201H. There are programs which can convert data files from one format to the other, and some microprocessors have special instructions to perform the conversion.对于字节和字而言,无论使用哪一种排列组织方式都不会影响CPU和计算机系统的性能。只要设计CPU处理一种特定的格式,就不存在谁比谁强的问题,主要的问题在于具有不同排列组织方式的CPU之间传输数据的问题,例如,如果一个低位优先结构的计算机传输0102 0304H的数据给一个高位优先结构的计算机,而没有转换数据,那么该高位优先结构计算机读出的值为0403 0201H。有程序可以将两种时局文件进行格式转换,并且某些处理器有特殊的指令可以执行这种转换。93
  • 94. 2.3.4 Multibyte Data Organization One other issue of concern for multibyte words is alignment. Modern microprocessors can read in more than one byte of data at a time. For example, the Motorola 68040 microprocessor can read in four bytes simultaneously. However, the four bytes must be in consecutive locations that have the same address except for the two least significant bits. This CPU could read locations 100, 101, 102, and 103 simultaneously, but not locations 101, 102, 103, and 104. This case would require two read operations, one for locations 100 (not needed), 101, 102, and 103, and the other for 104, 105 (not needed), 106 (not needed), and 107 (not needed).多字节的另一个值得关注的问题是对齐问题。现代微处理器在某一时刻可以读出多个字节。例如,摩托罗拉68040微处理器能同时读入4个字节的数据,然而,这4个字节必须在连续的单元中,它们的地址除了最低两位不同之外,其余的位均相同。该CPU可以同时读单元100、101、102和103,但不能同时读单元101、102、103和104,后者需要两个读操作,一个操作读100(不需要的)、101、102和103,另一个读104、105(不需要的)、106(不需要的)和107(不需要的)。94
  • 95. 2.3.4 Multibyte Data Organization Alignment simply means storing multibyte values in locations such that they begin at a location that also begins a multibyte read block. In this example, this means beginning multibyte values at memory locations that have addresses evenly divisible by four, thus guaranteeing that a four-byte value can be accessed by a single read operation.对齐简单地说就使存储多字节值的起始单元刚好是某个多字节读取模块的开始单元。在这个例子中,意味着多字节值开始存储的单元的地址要能被4整除,这样就保证该4字节值可在单一的一个读操作中存取到。95
  • 96. 2.3.4 Multibyte Data Organization Some CPUs, particularly RISC CPUs, require all data to be aligned. Other CPUs do not; they can usually align data internally. In general, nonaligned CPUs have more compact programs, because no locations are left unused by alignment. However, aligned CPUs can have better performance because they may need fewer memory read operations to fetch data and instructions.一些CPU,特别是精简指令系统CPU,需要所有的数据都对齐。其它的CPU不要求这样,它们通常能够在内部将数据对齐。一般来说,不要求对齐的CPU具有更紧凑的程序,因为没有单元因为要对齐而闲置不用。然而,对齐的CPU具有更好的性能,因为他们读取指令和数据是需要更少的存储器读操作。96
  • 97. 2.3.5 Beyond the Basics(基本功能的拓展 )The memory subsystem described in this chapter is sufficient for small, embedded computers. Personal computers and mainframes, however, require more complex hierarchical configurations. These computers include small, high-speed cache memory. The computer loads data from the physical memory into the cache; the processor can access data in the cache more quickly than it can access the same data in physical memory. Many microprocessors include some cache memory right on the processor chip. A computer that includes cache memory must also have a cache controller to move data between the cache and physical memory.本章描述的存储器子系统对于较小的、嵌入式计算机而言是足够的。然而,个人电脑和大型主机,需要更加复杂的层次结构。这些计算机包含体积小的、高速的高速缓冲存储器。计算机将数据从物理存储器中装载到高速缓冲中:处理器在高速缓冲中访问数据比在物理存储器中快得多。许多微处理器就在处理器芯片中含有一些高速缓冲存储器。含有高速缓冲存储器的计算机同时也要有一个高速缓冲控制器,用来在高速缓冲和物理存储器间传输数据。97
  • 98. 2.3.5 Beyond the BasicsAt the other extreme, modern computers include virtual memory. This mechanism uses a hard disk as a part of the computer's memory, expending the memory space of the computer while minimizing cost, since a byte of hard disk costs less than a byte of RAM. As with the cache, virtual memory needs a controller to move data between physical memory and the hard disk. 在另一端,现代计算机还具有一个虚拟存储器。这种机制用硬盘充当计算机存储器的一部分,扩大了计算机的存储空间,而且降低了价格,因为一个硬盘字节的价格比一个RAM字节要便宜的多。同高速缓冲一样,虚拟存储器也需要一个控制器以便在物理存储器和虚拟存储器之间传输数据。98
  • 99. 2.4 I/O Subsystem Organization and Interfacing New Words & Expressions: homogeneous adj.同类的, 均一的 circuitry n.电路, 线路 head n.磁头 wait state 等待状态 interrupt 中断 DMA=Direct Memory Access 直接存储器访问 99
  • 100. 2.4 I/O Subsystem Organization and Interfacing The CPU treats memory as homogeneous. From the CPU's perspective, each location is read from and written to in exactly the same way. Each memory location performs the same function--it stores a data value or an instruction for use by the CPU. CPU把存储器看作是同构的。从CPU的角度来看,每一个单元的读操作和写操作都是一样的,每一个单元执行同样的功能,即存储CPU使用的数据或指令。Input/output (I/O) devices, on the other hand, are very different. A personal computer's keyboard and hard disk perform vastly different functions, yet both are part of the I/O subsystem. Fortunately for the system designer, the interfaces between the CPU and the I/O devices are very similar. 另一方面,输入/输出设备是很不一样的。个人电脑的键盘和硬盘执行的是千差万别的功能,但它们同是I/O子系统的一部分。对系统设计者而言,幸运的是CPU和各I/O设备之间的接口是非常相似的。100
  • 101. 2.4 I/O Subsystem Organization and Interfacing As shown in Figure 2-1, each I/O device is connected to the computer system's address, data, and control buses. Each I/O device includes I/O interface circuitry; it is actually this circuitry that interacts with the buses. The circuitry also interacts with the actual I/O device to transfer data.如图2-1所示,每一个I/O设备与计算机系统的地址总线、数据总线和控制总线相连接,它们都包括I/O接口电路,与总线交互的实际上正是这一电路,同时它与实际的I/O设备交互来传输数据。101
  • 102. 2.4 I/O Subsystem Organization and Interfacing Figure 2-7 shows the generic interface circuitry for an input device, such as a keyboard. The data from the input device goes to the tri-state buffers. When the values on the address and control buses are correct, the buffers are enabled and data passes on to the data bus. The CPU can then read in this data. When the conditions are not right, the logic block does not enable the buffers; they are tri-stated and do not place data onto the bus.图2-7显示了一个输入设备(比如键盘)的一般接口电路。从输入设备来的数据传送到三态缓冲器,当地址总线和控制总线上的值正确时,缓冲器设为有效,数据传到数据总线上,然后CPU可以读取数据。当条件不正确时,逻辑块不会使缓冲器有效,它们保持高阻态,而且不把数据传到总线上。102
  • 103. 2.4 I/O Subsystem Organization and Interfacing The key to this design is the enable logic. Just as every memory location has a unique address, each I/O device also has a unique address. The enable logic must not enable the buffers unless it receives the correct address from the address bus. It must also get the correct control signals from the control bus. For an input device, an RD (or RD') signal must be asserted (as well as the IO/signal, or equivalent, in systems with isolated I/O).这一设计的关键在于使能逻辑。正如每一个存储单元都有一个惟一的地址一样,每一个I/O设备也有一个惟一的地址。除非从地址总线得到了正确的地址,否则使能逻辑不置缓冲器有效。同时,它还必须从控制总线上得到正确的控制信号。对于一个输入设备,RD(或者RD')信号必须有效(在独立系统中,还有信号,或其他等效的信号)。103
  • 104. 2.4 I/O Subsystem Organization and Interfacing The design of the interface circuitry for an output device, such as a computer monitor, is somewhat different than that for the input device. As shown in Figure 2-8, the tri-state buffers are replaced by a register. The tri-state buffers are used in input device interfaces to make sure that no more than one device writes data to the bus at any time. Since the output devices read data from the bus, rather that write data to it, they don't need the buffers. The data can be made available to all output devices; only the device with the correct address will read it in.输出设备(如显示器)接口电路的设计与输入设备的设计有所不同。如图2-8所示,寄存器代替了三态缓冲器。输入设备中使用三态缓冲器是为了确保在任何时刻都只有一个设备向总线写数据,而输出设备是从总线读取数据,不是写数据,因此不需要缓冲器。数据对于所有的输出设备都可获得,但只有具有正确地址的设备才会读取它。104
  • 105. 2.4 I/O Subsystem Organization and Interfacing The load logic plays the role of the enable logic in the input device interface. When this logic receives the correct address and control signals, it asserts the LD signal of the register, causing it to read data from the system's data bus. The output device can then read the data from the register at its leisure while the CPU performs other tasks. 装载逻辑发挥着输入设备接口中使能逻辑的作用。当此逻辑获得正确的地址信号和控制信号后,它发出寄存器的LD信号,促使它从系统数据总线上读取数据。然后输出设备可以在其空闲的时候从寄存器中读取该数据,同时CPU可以执行其他的任务。105
  • 106. 2.4 I/O Subsystem Organization and Interfacing A variant of this design replaces the register with tri-state buffers. The same logic used to load the register is used to enable the tri-state buffers instead. Although this can work for some designs, the output device must read in data while the buffers are enabled. Once they are disabled, the outputs of the buffers are tri-stated and the data is no longer available to the output device.该设计也可以用三态缓冲器代替寄存器。装载寄存器的逻辑同样用于使能三态缓冲器。虽然对于某些设计这是可行的,但是输出设备必须在缓冲器有效时读入数据。一旦缓冲器被禁止,其输出就是三态,该数据也就不再能够供输出设备使用。106
  • 107. 2.4 I/O Subsystem Organization and Interfacing Some devices are used for both input and output. A personal computer's hard disk drive falls into this category. Such a device requires a combined interface that is essentially two interfaces, one for input and the other for output. Some logic elements, such as the gates that check the address on the address bus, can be used to generate both the buffer enable and register load signals有些设备既用于输入又用于输出,个人电脑中的硬盘驱动器就属于这一类。这样的设备需要一个组合接口,本质上是两个接口,一个用于输入,另一个用于输出。一些逻辑元件(比如检查地址总线上的地址是否正确的门电路)既可以用来产生缓冲器的使能信号,有可以用来产生寄存器的装载信号。107
  • 108. 2.4 I/O Subsystem Organization and Interfacing I/O devices are much slower than CPUs and memory. For this reason, they can have timing problems when interacting with the CPU. To illustrate this, consider what happens when a CPU wants to read data from a disk. It may take the disk drive several milliseconds to position its heads properly to read the desired value. In this time, the CPU could have read in invalid data and fetched, decoded, and executed thousands of instructions.I/O设备比CPU和存储器慢得多。基于这个原因,当它们与CPU交互时,就可能存在时序上的问题。为了说明这一点,考虑当CPU想要从硬盘中读取数据时会发生的情况,这可能要消耗磁盘驱动器几个毫秒来正确的定位磁头,以便读取想要的数值,而在这段时间里,CPU可能已经读入了不正确的数据,并且读取、译解和执行了成千上万条指令。108
  • 109. 2.4 I/O Subsystem Organization and Interfacing Most CPUs have a control input signal called READY (or something similar). Normally this input is high. When the CPU outputs the address of the I/O device and the correct control signals, enabling the tri-state buffers of the I/O device interface, the I/O device sets READY low. The CPU reads this signal and continues to output the same address and control signals, which cause the buffers to remain enabled. In the hard disk drive example, the drive rotates the disk and positions its read heads until it reads the desired data. 大多数CPU都有一个控制输入信号,叫做就绪信号(READY)(或其他意思相近的名称),通常它为高电平。当CPU输出某I/O设备的地址和正确的控制信号,促使I/O设备接口的三态缓冲器有效时,该I/O设备置READY信号为低电平。CPU读取这一信号,并且继续输出同样的地址信号和控制信号,使缓冲器保持有效。在硬盘驱动器的例子中,此时驱动器旋转磁头,并且定位读写头,直到读到想要要的数据为止。109
  • 110. 2.4 I/O Subsystem Organization and Interfacing The CPU then reads the data from the bus and continues its normal operation. The extra clock cycles generated by having READY set low are called wait states. CPUs can also use the READY signal to synchronize data transfers with the memory subsystem.然后它通过缓冲器将数据输出到数据总线上,并重新设置READY为高电平。这时CPU才从总线上读入数据,之后继续它的正确操作。设置READY为低电平而生成的附加时钟周期叫做等待状态。CPU同样也可以使用READY信号来同步与存储器子系统之间的数据传输。110
  • 111. 2.4 I/O Subsystem Organization and Interfacing These I/O interfaces are fine for small computers, such as the microwave oven controller, but they suffer from poor performance in larger computer systems. In all but the smallest systems, it is not acceptable for the CPU to have to wait thousands of clock cycles for data from an I/O device. Many systems use interrupts so they can perform useful work while waiting for the much slower I/O devices. 这些I/O接口对于小型的计算机而言已经很好了,比如说微波炉控制器,但是在大型的计算机系统中它们的性能则很差。在除最小系统以外的所有系统中,让CPU等待成千上万个时钟周期方从I/O设备中得到数据是不能接收的,为此,许多系统都使用了中断机制,以便CPU在等待慢得多的I/O设备时,可以执行其他有用的工作。111
  • 112. 2.4 I/O Subsystem Organization and Interfacing These I/O interfaces are also not suited to large data transfers. In the systems in this chapter, each byte of data transferred between an I/O device and memory must pass through the CPU. This is inefficient for many common operations, such as loading a program from disk into memory. Direct memory access, DMA, is a method used to bypass the CPU in these transfers, thus performing them much more quickly. 这些I/O接口也不适合大量的数据传输。在本章的系统中,I/O设备和存储器之间传输的每一个字节都必须通过CPU,这对于许多常见的操作(例如从磁盘向主机存装载一个程序)来说效率低下。直接存储器访问就是在数据传输中绕过CPU的一种方法,因此执行起来速度很快。112
  • 113. 计算机英语专业词汇的构成 113
  • 114. 一、派生词(derivation) 1.前缀 采用前缀构成的单词在计算机专业英语中占了很大比例,通过下面的实例可以了解这些常用的前缀构成的单词。 multi-多 hyper-超级 super 超级 multiprogram 多道程序 hypercube 超立方 superhighway 超级公路 inter-相互、在...间 micro-微型 tele-远程的 interface接口、界面 microprocessor 微处理器 telephone 电话 interlace 隔行扫描 microkernel 微内核 teletext 图文电视 单词前缀还有很多,其构成可以同义而不同源(如拉丁、希腊),可以互换,例如: multi, poly 相当于many 如: multimedia多媒体, polytechnic各种工艺的 uni, mono 相当于single 如: unicode统一的字符编码标准, monochrome单色 bi, di 相当于 twice 如: binomial 二项式,dibit双位 equi,iso 相当于equal 如: equality等同性, isochromatic等色的, simili, homo 相当于same 如: similarity类似, homogeneous同类的 semi,hemi 相当于half 如: semiconductor半导体, hemicycle半圆形 hyper, super 相当于over 如: hypertext超文本, supercomputer超级计算机114
  • 115. 一、派生词(derivation) 2.后缀 后缀是在单词后部加上构词结构,形成新的单词。如: -scope 探测仪器 -meter 计量仪器 -graph 记录仪器 microscope显微镜 barometer 气压表 tomograph X线体层照相 telescope 望远镜 telemeter 测距仪 telegraph 电报 spectroscope 分光镜 spectrometer 分光仪 spectrograph 分光摄像仪 -able可能的 -ware 件(部件) -ity 性质 enable 允许、使能 hardware 硬件 reliability 可靠性 disable 禁止、不能 software 软件 availability 可用性 programmable 可编程的 firmware 固件 accountability 可核查性 portable 便携的 groupware 组件 integrity 完整性 scalable 可缩放的 freeware 赠件 confidentiality 保密性115
  • 116. 二、复合词(compounding) 复合词是科技英语中另一大类词汇,其组成面广,通常分为复合名词、复合形容词、复合动词等。复合词通常以小横杠“-”连接单词构成,或者采用短语构成。有的复合词进一步发展,去掉了小横杠,并经过缩略成为另一类词类,即混成词。复合词的实例有: -based基于,以……为基础 -centric 以……为中心的 rate-based 基于速率的 client-centric 以客户为中心的 credit-based 基于信誉的 user-centric 以用户为中心的 file-based 基于文件的 host-centered 以主机为中心的 -oriented 面向……的 -free 自由的,无关的 object-oriented 面向对象的 lead-free 无线的 market-oriented 市场导向 jumper-free 无跳线的 process-oriented 面向进程的 paper-free 无纸的 info-信息,与信息有关的 envent-事件的 info-channel 信息通道 envent-driven 事件驱动的 info-tree 信息、树 envent-oriented 面向事件的 info-world 信息世界 event-based 基于事件的116
  • 117. 二、复合词(compounding) 此外,以名词 + 动词-ing 构成的复合形容词形成了一种典型的替换关系,即可以根据需要在结构中代入同一词类而构成新词,它们多为动宾关系。如: man-carrying aircraft 载人飞船 earth-moving machine 推土机 time-consuming operation 耗时操作 ocean-going freighter 远洋货舱 然而,必须注意,复合词并非随意可以构造,否则会形成一种非正常的英语句子结构。虽然上述例子给出了多个连接单词组成的复合词,但不提倡这种冗长的复合方式。对于多个单词的非连线形式,要注意其顺序和主要针对对象。 此外还应当注意,有时加连字符的复合词与不加连字符的词汇词意是不同的,必须通过文章的上下文推断。如: force-feed 强迫接受(vt.),而force feed 则为“加压润滑”。 随着词汇的专用化,复合词中间的连接符被省略掉,形成了一个单词,例如: videotape 录像带 fanin 扇入 fanout 扇出 online 在线 onboard 在板 login 登录 logout 撤消 pushup 拉高 popup 弹出117
  • 118. 三、混成词(blending) 混成词不论在公共英语还是科技英语中也大量出现,也有人将它们称为缩合词(与缩略词区别)、融会词,它们多是名词,也有地方将其作为动词用,对这类词汇可以通过其构词规律和词素进行理解。这类词汇将两个单词的前部拼接、前后拼接或者将一个单词前部与另一词拼接构成新的词汇,实例有: brunch (breakfast + lunch) 早中饭 smog (smoke +fog) 烟雾 codec (coder+decoder) 编码译码器 compuser (computer+user) 计算机用户 transeiver (transmitter+receiver) 收发机 syscall (system+call) 系统调用 mechatronics (mechanical+electronic) 机械电子学 calputer (calculator+computer) 计算器式电脑118
  • 119. 四、缩略词(shortening) 缩略词是将较长的英语单词取其首部或者主干构成与原词同义的短单词,或者将组成词汇短语的各个单词的首字母拼接为一个大写字母的字符串。随着科技发展,缩略词在文章索引、前言、摘要、文摘、电报、说明书、商标等科技文章中频繁采用。 1.压缩和省略 将某些太长、难拼、难记、使用频繁的单词压缩成一个短小的单词,或取其头部、或取其关键音节。如: f1u=influenza 流感 1ab=laboratory 实验室 math=mathematics 数学 iff=if only if 当且仅当 rhino=rhinoceros 犀牛 ad=advertisement 广告119
  • 120. 四、缩略词(shortening) 2.缩写 (acronym) 将某些词组和单词集合中每个实意单词的第一或者首部几个字母重新组合,组成为一个新的词汇,作为专用词汇使用。在应用中它形成三种类型,即: 1) 通常以小写字母出现,并作为常规单词 flops (floating-point Operation Per Second) 每秒浮点运算次数 spool (simultaneous peripheral operation on line) 假脱机 2) 以大写字母出现,具有主体发音音节 BASIC (Beginner's All-purpose Symbolic Instruction Code) 初学者通用符号指令代码 FORTRAN (Formula Translation) 公式翻译(语言) COBOL (Common Business Oriented Language) 面向商务的通用语言 3) 以大写字母出现,没有读音音节,仅为字母头缩写 RISC (Reduced Instruction Set Computer) 精简指令集计算机 CISC (Complex Instruction Set Computer) 复杂指令集计算机 ADE (Application Development Environment) 应用开发环境 PCB (Process Control Block) 进程控制块 CGA (Color Graphics Adapter) 彩色图形适配器120
  • 121. 五、借用词 借用词一般来自厂商名、商标名、产品代号名、发明者名、地名等,它通过将普通公共英语词汇演变成专业词意而实现。有的则是将原来已经有的词汇赋予新的含义。例如: woofer 低音喇叭 tweeter 高音喇叭 flag标志、状态 cache 高速缓存 semaphore 信号量 firewall 防火墙 mailbomb 邮件炸弹 scratch pad 高速缓存 fitfall 专用程序入口 在现代科技英语中借用了大量的公共英语词汇、日常生活中的常用词汇,而且,以西方特有的幽默和结构讲述科技内容。这时,读者必须在努力扩大自己专业词汇的同时,也要掌握和丰富自己的生活词汇,并在阅读和翻译时正确采用适当的含义。 121
  • 122. Computer English Chapter 3 Number Systems and Boolean Algebra
  • 123. Key points: useful terms and definitions of Number system and Boolean Algbra Difficult points: Conversion of the Number Systems and Boolean Algbra123
  • 124. Requirements:1. Concepts of Number System and their conversion 2. Boolean Algebra 3. Moore’s Law 4. 科技英语中数学公式的读法 124
  • 125. New Words & Expressions: hexadecimal adj.十六进制的; n.十六进制 radix n.根, 基数 octal adj.八进制的; n.八进制 alphabet n.字母表 fractional adj.分数的, 小数的 whole number n.整数 remainder n.余数 significant figure n.有效数字 quotient n.商 algorithm n.算法 complement n. 补码,余角 carry n.进位 3.1 Number Systems Abbreviations: Binary-coded hexadecimal (BCH) 二进制编码的十六进制125
  • 126. The use of the microprocessor requires a working knowledge of binary, decimal, and hexadecimal numbering systems. This section provides a background for those who are unfamiliar with number systems. Conversions between decimal and binary, decimal and hexadecimal, and binary and hexadecimal are described.3.1 Number Systems 使用微处理器需要掌握二进制、十进制和十六进制数制系统的基本知识,本节为那些不熟悉数制系统的读者提供这方面的背景知识。说明了十进制与二进制之间、十进制与十六进制之间,及二进制与十六进制之间的转换。126
  • 127. Before numbers are converted from one number base to another, the digits of a number system must be understood. Early in our education, we learned that a decimal, or base 10, number was constructed with 10 digits: 0 through 9. The first digit in any numbering system is always a zero. For example, a base 8 (octal) number contains 8 digits: 0 through 7; a base 2 (binary) number contains 2 digits: 0 and 1. 3.1.1 Digits 将数从—种数制向另一种数制转换之前,必须了解数的计数系统。在早期教育中,我们已学习了十进制数,或以10为基的数,它由10个数字组成:0到9。任何计数制的第一个数字总是零,这种规则适用于任何其他数制。例如,以8为基的数(八进制)包含8个数字:0到7,而以2为基的数(二进制)包含2个数字:0和 l。127
  • 128. If the base of a number exceeds 10, the additional digits use the letters of the alphabet, beginning with an A, For example, a base 12 number contains 12 digits: 0 through 9, followed by A for 10 and B for 11, Note that a base 10 number does not contain a 10 digit, just as a base 8 number does net contain an 8 digit. The most common numbering systems used with computers are decimal, binary, and hexadecimal (base 16). (Many years ago octal numbers were popular.) Each system is described and used in this section of the chapter.3.1.1 Digits 如果基数大于10,其余数字用从A开始的字母表示,例如,以12为基的数包含12个数字,0到9,之后用A代表10,B代表11。注意,以10为基的数不包含数字10,如同以8为基的数不包括数字8一样。计算机中最通用的计数制是十进制、二进制、八进制和十六进制(基为16)。每种计数制都将在本节中进行说明和应用。128
  • 129. Once the digits of a number system are understood, larger numbers are constructed by using positional notation. In grade school, we learned that the position to the left of the units position was the tens position, the position to the left of the tens position was the hundreds position, and so forth. (An example is the decimal number 132: This number has 1 hundred, 3 tens, and 2 units.) What probably was not learned was the exponential value of each position: The units position has a weight of 100 or 1; the tens position has weight of 101, or 10; and the hundreds position has a weight of 102, or 100. 3.1.2 Positional Notation 一旦我们理解了计数制的数字后,就可用位计数法构造更大的数值。在小学时我们都学过个位的左边一位是十位,十位左边一位是百位,以此类推(例如十进制数132,这个数字有—个百,三个十和两个一)。或许我们没有学过每个位的指数值:个位的权为l00,即1;十位的权为101或10;而百位的权为102或l00。129
  • 130. The exponential powers of the positions are critical for understanding numbers in other numbering systems. The position to the left of the radix (number base) point, called a decimal point only in the decimal system, is always the units position in any number system. For example, the position to the left of the binary point is always 20 or 1; the position to the left of the octal point is 80 or 1. In any case, any number raised to its zero power is always 1, or the units position.3.1.2 Positional Notation 位的指数幂在理解其他计数制中的数时是个关键。基数小数点,在十进制中称为十进制小数点,其左边的位在任何数制中都是个位。例如,二进制小数点左边的位是20或1。而八进制小数点左边的位是80或1。在任何情况下,任何数的零次幂总是1,或1个单位。130
  • 131. The position to the left of the units position is always the number base raised to the first power; in a decimal system, this is l01, or l0. In a binary system, it is 21, or 2; and in an octal system it is 81, or 8. Therefore, an 11 decimal has a different value from an 11 binary. The 1l decimal is composed of 1 ten plus 1 unit and has a value of 11 units; while the binary number 11 is composed of 1 two plus 1 unit, for a value of 3 decimal units. The 11 octal has a value of 9 units.3.1.2 Positional Notation 个位左边的位总是基数的1次幂,在十进制系统中是101,或10;在二进制中是21,或2;而在八进制中是81,或8。因此,十进制的11与二进制的11具有不同的数值。十进制11表示—个10加上一个1,其值为11;二进制11表示—个2加上—个1,其值为3;八进制11的值为9。131
  • 132. In the decimal system, positions to the right of the decimal point have negative powers. The first digit to the right of the decimal point has a value of 10-1, or 0.1. In the binary system, the first digit to the right of the binary point has a value of 2-1, or 0.5. In general, the principles that apply to decimal numbers also apply to numbers in any other number system.3.1.2 Positional Notation 在十进制系统中,对于十进制小数点右边的位,它的幂为负数。十进制小数点右边第一位数的值为10-1,或0.1。在二进制中,二进制小数点右边第—位数的值为2-1或0.5。一般来说,十进制使用的计数法可以用于任何其他数制。132
  • 133. Example 3-1 shows a 110.101 in binary (often written as 110.1012). It also shows the power and weight or value of each digit position. To convert a binary number to decimal, add the weights of each digit to form its decimal equivalent. The 110.1012 is equivalent to a 6.625 in decimal (4+2+0.5+ 0.125). Notice that this is the sum of 22 (or 4) plus 21 (or 2), but 20 (or 1) is not added because there are no digits under this position. The fraction part is composed of 2-1 (0.5) plus 2-3 (or.125), but there is no digit under the 2-2 (or .25).3.1.2 Positional Notation 例3-1给出了一个二进制数110.101(通常写成110.1012),也给出了这个数每个位的幂、权和值。为了把二进制数转换为十进制,将每位数字的权相加,就得到了它的等效十进制值。二进制110.101等于十进制的6.625(4+2+0.5+0.125)。注意,这个和的整数部分是由22(4)加21(2)构成,之所以没有用20(1)是因为这个位的数为零。小数部分由2-1(0.5),加2-3(0.125)构成,但是没有用2-2(0.25)。133
  • 134. The prior examples have shown that to convert from any number base to decimal, determine the weights or values of each position of the number, and then sum the weights to form the decimal equivalent. Suppose that a 125.78 octal is converted to decimal. To accomplish this conversion, first write down the weights of each position of the number. This appears in Example 3-2. The value of 125.78 is 85.875 decimal, or 164 plus 2 8 plus 51 plus 7 .125.3.1.3 Conversion to Decimal 前面的例子说明了将任何其他基数的数转换为十进制数时,十进制数的值取决于该数每个位上的权或值,它们的和就是等效的十进制数值。假定要将125.78(八进制)转换为十进制。为了完成这个转换,首先写出该数每一位数的权,如例3-2所示,125.78的值是十进制的85.875,即1 64+2 8+5  1+7 0.125。134
  • 135. Notice that the weight of the position to the left of the units position is 8. This is 8 times 1. Then notice that the weight of the next position is 64, or 8 times 8. If another position existed, it would be 64 times 8, or 51 2. To find the weight of the next higher-order position, multiply the weight of the current position by the number base (or 8, in this example). To calculate the weights of position to the right of the radix point, divide by the number base. In the octal system, the position immediately to the fight of the octal point is 1/8, or .125. The next position is .125/8, or .015625, which can also be written as 1/64. 3.1.3 Conversion to Decimal 注意,该数个位左边那位的权是8(18)。再前一位的权是64(88)。如果存在更前一位,则其权将是512(648)。将当前位的权乘上基数,就可得到更高一位的权(本例中是乘8)。而计算小数点右边那些位的权,需要用基数去除。在八进制中,紧跟八进制小数点右边的那位的权是1/8,即0.125。下一位是0.125/8,即0.015625,也可以写成1/64。 135
  • 136. Hexadecimal numbers are often used with computers. A 6A.CH (H for hexadecimal) is illustrated with its weights in Example 3-3. The sum of its digits is 106.75, or 106. The whole number part is represented with 616 plus 10 (A)1. The fraction part is 12 (C) as a numerator and 16 (16-1) as the denominator, or 12/16, which is reduced to 3/4.3.1.3 Conversion to Decimal 计算机经常使用十六进制。例3-2给出了一个十六进制数6A.CH(H表示十六进制),以及它的权。它的各位数值之和是106.75,即106。整数部分用616加10(A) 1表示;分数部分用12(C)作为分子,16作为分母(16-1),或表示为12/16,化简得3/4。 136
  • 137. Conversions from decimal to other number systems are more difficult to accomplish than conversion to decimal. To convert the whole number portion of a number to decimal, divide by the radix. To convert the fractional portion, multiply by the radix. 3.1.4 Conversion From Decimal 由十进制转换成其他进制比由其他进制转换成十进制困难。转换十进制整数部分时,要用基数去除,转换分数部分时,要用基数去乘它们。137
  • 138. Whole Number Conversion from Decimal. To convert a decimal whole number to another number system, divide by the radix and save the remainders as significant digits of the result. An algorithm for this conversion as is follows: 1. Divide the decimal number by the radix (number base). 2. Save the remainder (first remainder is the least significant digit), 3. Repeat steps 1 and 2 until the quotient is zero.3.1.4 Conversion From Decimal 转换十进制整数部分 将十进制整数转换成其他数制时,要用基数去除,并且保存余数,作为结果的有效数字。这种转换的算法如下: 1. 用基数除十进制数。 2. 保存余数(最先得到的余数是最低有效位数字)。 3. 重复步骤l和2,直到商为零。138
  • 139. Converting from a Decimal Fraction. Conversion from decimal fraction to another number base is accomplished with multiplication by the radix. For example, to convert a decimal fraction into binary, multiply by 2. After the multiplication, the whole number portion of the result is saved as a significant digit of the result, and the fractional remainder is again multiplied by the radix. When the fraction remainder is zero, multiplication ends. Note that some numbers are never-ending. That is, a zero is never a remainder. An algorithm for conversion from a decimal fraction is as follows3.1.4 Conversion From Decimal 转换十进制小数部分 转换10进制小数部分是用基数乘来完成的。例如,要将十进制 小数转换成二进制,要用2乘。乘法之后,乘积的整数部分保存起来作为结果的一个有效位,剩余的小数再用基数2去乘。当剩余的小数部分为0时,乘法结束。有些数可能永远不会结束,即余数总不为0。转换十进制小数部分的算法如下:139
  • 140. 1. Multiply the decimal fraction by the radix (number base). 2. Save the whole number portion of the result (even if zero) as a digit. Note that the first result is written immediately to the fight of the radix point. 3. Repeat steps 1 and 2, using the fractional part of step 2 until the fractional part of step 2 is zero.3.1.4 Conversion From Decimal 1. 用基数乘十进制小数。 2. 保存结果的整数部分(即使是零)作为一位数。注意,第一个得到的结果写在紧挨着小数点的右边。 3. 用步骤2的小数部分重复步骤l和2,直到步骤2的小数部分是零。140
  • 141. Binary-coded hexadecimal (BCH) is used to represent hexadecimal data in binary code. A binary-coded hexadecimal number is a hexadecimal number written so that each digit is represented by a 4-bit binary number. The values for the BCH digits appear in Table 3--1. Hexadecimal numbers are represented in BCH code by converting each digit to BCH code, with a space between each coded digit. 3.1.5 Binary-Coded Hexadecimal 二进制编码的十六进制(BCH)是用二进制编码表示的十六进制数据,二进制编码的十六进制数是将十六进制数的每一位都用4位二进制数表示。表3-1给出了BCH数的值。 用BCH表示十六进制数时,将每个十六进制数字都转换成BCH码,并且每个数位之间用空格分开。 141
  • 142. The purpose of BCH code is to allow a binary version of a hexadecimal number to be written in a form that can easily be converted between BCH and hexadecimal. Example 3-8 shows a BCH coded number converted back to hexadecimal code. 3.1.5 Binary-Coded Hexadecimal BCH码的目的在于能将十六进制数以二进制的形式写出,使BCH与十六进制之间转换很容易。例3-8表示如何将BCH代码数据转换为十六进制码。142
  • 143. At times, data are stored in complement form to represent negative numbers. There are two systems that are used to represent negative data: radix and radix -1 complements. The earliest system was the radix -1 complement, in which each digit of the number is subtracted from the radix -1 to generate the radix -1 complement to represent a negative number. 3.1.6 Complements 有时,数据以补码的形式存储,以便表示负数。有两种表示负数的方式:补码和反码(基数减l的补),最早的方式是反码。为了得到负数的反码表示,用基数-1减去该数的每一个数位上的数字。143
  • 144. Example 3-9 shows how the 8-bit binary number 01001100 is one's (radix -1) complemented to represent it as a negative value. Notice that each digit of the number is subtracted from one to generate the radix -1 (one's) complement. In this example, the negative of 01001100 is 10110011. The same technique can be applied to any number system, as illustrated in Example 3-10, in which the fifteen's (radix -l) complement of a 5CD hexadecimal is computed by subtracting each digit from a fifteen.3.1.6 Complements 例3-9表示了如何将8位二进制数01001100对l取补(基数减1的补),以便表示成—个负数。注意,用1减去该数的每一位数字,以便生成反码。在此例中,01001100的负数是10110011。同样的技术可适用于任何数制。如例3-10所示,十六进制数5CD的反码是从15(基-1)中减去它的每一位数字得到的。 144
  • 145. Today, the radix -1 complement is not used by itself; it is used as a step for finding the radix complement. The radix complement is used to represent negative numbers in modern computer systems. (The radix -1 complement was used in the early days of computer technology.) The main problem with the radix -1 complement is that a negative or a positive zero exists; in the radix complement system, only a positive zero can exist. 3.1.6 Complements 如今,反码已不单独使用,而作为求补码的一个步骤使用,补码是当代计算机系统表示负数的方法(反码用于早期的计算技术中)。反码的主要问题是它存在负零或者正零,而补码系统中只能存在正零。145
  • 146. To form the radix complement, first find the radix -1 complement, and then add a one to the result. Example 3-11 shows how the number 0100 1000 is converted to a negative value by two's (radix) complementing it. 3.1.6 Complements 为得到补码,先求反码,然后将1加到结果上。例3-11表示了如何通过对2(基为2)取补的方式,将数01001000转换成负数。146
  • 147. To prove that a 0100 1000 is the inverse (negative) of a 1011 0111, add the two together to form an 8-digit result. The ninth digit is dropped and the result is zero because a 0l00100 is a positive 72, while a 1011 0111 is a negative 72. The same technique applied to any number system. Example 3-12 shows how the inverse of a 345 hexadecimal is found by first fifteen's complementing the number, and then by adding one to the result to form the sixteen’s complement. As before, if the original 3-digit number 345 is added to the inverse of CBB, the result is a 3-digit 000. As before, the fourth bit (carry) is dropped. This proves that 345 is the inverse of CBB. 3.1.6 Complements 为验证0100 1000是1011 1000的反(负数),将两者相加得到一个8位结果。去掉第9位数字,结果是零。因为0100 1000是正数72,而1011 0111是负数72。同样的枝术可用于任何数制。例3-12表示如何求十六进制数345的负数,首先求该数15的补,然后将1加到结果上,得到16的补,同前面类似,如把原来的3位数345加上其负数CBB,则结果是3位000,第4位(进位)被丢掉。这证明了345是CBB的反。147
  • 148. The concept of a Boolean algebra was first proposed by the English mathematician George Boole in 1847. Since that time, Boole’s original conception has been extensively developed and refined by algebraists and logicians. The relationships among Boolean algebra, set algebra, logic, and binary arithmetic have given Boolean algebras a central role in the development of electronic digital computers. 3.2 Boolean Algebra 布尔代数的概念最初是由英国数学家George Boole于1847年提出来的,从那时起,代数学家和逻辑学家们更广泛地发展了Boole最初的概念,并使之更加精练。由于布尔代数、集合代数、逻辑学和二进制算术之间的内在联系,使得布尔代数的理论在电子计算机的发展中起到举足轻重的作用。148
  • 149. The most intuitive development of Boolean algebras arises from the concept of a set algebra. Let S={a, b, c} and T={a, b, c, d, e} be two sets consisting of three and five elements, respectively. We say that S is a subset of T, since every element of S (namely, a, b, and c) belongs to T. Since T has five elements, there are 25 subsets of T, for we may choose any individual element to be included or omitted from a subset. Note that these 32 subsets include T itself and the empty set, which contains no elements at all. If T contains all elements of concern, it is called the universal set. Given a subset of T, such as S, we may define the complement of S with respect to a universal set T to consist of precisely those elements of T which are not included in the given subset.3.2 Boolean Algebra 布尔代数最直觉的发展产生于集合代数的概念。设S={a,b,c}和T={a,b,c,d,e}分别为两个含有三个和五个元素的集合。由于S中的每一个元素(a,b,c)都属于T,所以我们说S是T的一个子集。由于T有五个元素,因而T共有25个子集,这是因为我们可以选择任何一个元素使其包含于某个子集中或从该子集中删除。应该注意到这32个子集中包含T本身和空集(空集即不含任何元素的集合)。如果T包含了所讨论的所有元素,则称之为全集。给定T的一个子集,例如子集S,我们可以定义一个关于全集T的S的补集。其中正好包含那些不在子集S中而在T中的元素。149
  • 150. Thus, S as above defined has its complement (with respect to T) . The union of any two sets (subsets of a given set) consists of those elements that are in one or the other or in both given sets; the intersection of two sets consists of those elements that are in both given sets. We use the symbol ∪ to denote the union, and ∩ to denote the intersection of two sets. For example, if B={b, d, e}, then B∪S={a, b, c, d, e}, and B∩S={b}.3.2 Boolean Algebra 于是,如上定义的集合S就有一个它的补集(相对于集合T)。任何两个集合(已给定集合的若干子集)的并集包含了出现于这两个子集中某一个集合或同时出现于这两个集合中的所有元素;两个集合的交集包含了同时出现于这两个集合中的元素。我们用符号“∪”来表示两个集合的“并(运算)”,用“∩” 来表示两个集合的“交(运算)”。例如,如果B={b,d,e},那么,B∪S={a,b,c,d,e},B∩S={b}。150
  • 151. While other set operations may be defined, the operations of complementation union and intersection are of primary interest to us. A Boolean algebra is a finite or infinite set of elements together with three operations—negation, addition, and multiplication—that correspond to the set operations of complementation, union, and intersection, respectively. Among the elements of a Boolean algebra are two distinguished elements: 0, corresponding to the empty set; and 1, corresponding to the universal set. 3.2 Boolean Algebra 虽然我们可以定义其他一些集合运算,但求补、并和交运算是我们最感兴趣的三个集合运算。一个布尔代数就是一个有限集或无限集,以及建立在该有限集或无限集上的三种运算——否定、加或乘,这三个运算分别对应于集合的求补、并和交运算。在布尔代数的元素中有两个特殊的元素:0,对应于空集;1,对应于全集。151
  • 152. For any given element of a Boolean algebra, there is a unique complement a' with the property that a+a'=1 and aa'=0. Boolean addition and multiplication are associative and commutative, as are ordinary addition and multiplication, but otherwise have somewhat different properties. The principal properties are given in Table 3-2, where a, b, and c are any elements of a Boolean algebra.3.2 Boolean Algebra 对于一个布尔代数中任意给定元素a,都有一个唯一的补a,它满足a+a=1和aa=0。布尔加和布尔乘与普通的加和乘一样,满足结合律和交换律,但除此之外含有一些不太相同的特性。其主要特性由表3-2给出,其中a, b和c是一个布尔代数中的任意元素。152
  • 153. 3.2 Boolean Algebra Table 3-2Distributivity 分配律 a(b+c)=ab+ac a+(bc)=(a+b)(a+c)Idempotency 同一律 a+a=a aa=aAbsorption laws 吸收律 a+ab=a a(a+b)=aDeMorgan’s laws德摩根定理 (a+b)'=a'b' (ab)'=a'+b'153
  • 154. Since a finite set of n elements has exactly 2n subsets, and it can be shown that the finite Boolean algebras are precisely the finite set algebras, each finite Boolean algebra consists of exactly 2n elements for some integer n. For example, the set algebra for the set T defined above corresponds to a Boolean algebra of 32 elements. 3.2 Boolean Algebra 由于n个元素的有限集有且只有2n个子集,而且很显然有限布尔代数一定是有限集合代数,所以对某个整数n而言,每个有限布尔代数也有且只有2n个元素。例如,上文定义的集合T的集合代数就对应一个有32个元素的布尔代数。154
  • 155. While it is possible to use a different symbol to denote each element of a Boolean algebra, it is often more useful to represent the 2n elements of a finite Boolean algebra by binary vectors having n components. With such a representation the operations of the Boolean algebra are accomplished componentwise by considering each component as an independent two-element Boolean algebra. This corresponds to representing subsets of a finite set by binary vectors. 3.2 Boolean Algebra 虽然我们可以用不同的符号来表示布尔代数中的每一个元素,但最常用的方法是用一个有n个分量的二进制向量来表示一个有限布尔代数的2n个元素。用这样一种表示方法,布尔代数的所有运算都以分量的形式完成,而每一个分量被认为是一个独立的二值布尔代数。这种做法对应于用二进制向量来表示一个有限集的子集。155
  • 156. For example, since the set T has five elements, we may represent its subsets by five-component binary vectors, each component denoting an element of the set T. A numeral l in the i-th component of the vector denotes the inclusion of the i-th element of that particular subset; a 0 denotes its exclusion. Thus, the subset S={a, b, c} has the binary vector representation {1,1,1,0,0}. The set operations become Boolean operations on the components of the vectors. This representation of sets, and the correspondence to Boolean or logical operations, is very useful in information retrieval. Because of it, sets of document and query characteristics may be easily and rapidly matched.3.2 Boolean Algebra 例如,由于集合T有5个元素,所以我们可以用5个分量的二进制向量表示它的子集,其中每一个分量表示集合T的一个元素。向量中的第i个分量为数字1表示集合T的第i个元素在某一特定子集中,用数字0表示不在某一特定子集中。于是,子集S={a,b,c}可用二进制向量表示为{1,1,1,0,0}。集合运算变成了向量分量上的布尔运算。集合的这种表示方法以及相应的布尔或逻辑运算,对于信息检索是非常有用的。由于这一原因,文件的集合和查询特性可以很容易而迅速地得到匹配。156
  • 157. 数学公式的读法(Pronunciation of mathematical expressions)1 逻辑(Logic) there exists for all p q p implies q / if p, then q pq p if and only if q p is equivalent to q p and q are equivalent157
  • 158. 2 集合(Sets) xA x belongs to A / x is an element (or a member) of A xA x does not belong to A / x is not an element (or a member) of A AB A is contained in B / A is a subset of B AB A contains B / B is a subset of A AB A cap B / A meet B/ A intersection B AB A cup B/ A join B / A union B B/A A minus B/the difference between A and B A×B A cross B / the Cartesian product of A and B(A与B的笛卡尔积) 数学公式的读法(Pronunciation of mathematical expressions)158
  • 159. 数学公式的读法(Pronunciation of mathematical expressions)3 实数(Real numbers) x+1 x plus one x-1 x minus one x±1 x plus or minus one xy xy / x multiplied by y (x-y)(x+y) x minus y, x plus y x over y = the equals sign x=5 x equals 5 / x is equal to 5 x≠5 x (is) not equal to 5 x≡y x is equivalent to (or identical with) y159
  • 160. 3 实数(Real numbers) x>y x is greater than y x≥y x is greater than or equal to y x< y x is less than y xy x is less than or equal to y 0
  • 161. 数学公式的读法(Pronunciation of mathematical expressions)3 实数(Real numbers) n! n factorial (x+y)2 x plus y all squared xi xi / x subscript i / x suffix i / x sub i the sum from i equals one to n ai / the sum as i runs from 1 to n of the ai x over y all squared x hat x bar x tilde161
  • 162. 数学公式的读法(Pronunciation of mathematical expressions)4 线性代数(Linear algebra) ||A|| the norm (or modulus) of x OA / vector OA OA / the length of the segment OA AT A transpose / the transpose of A A-1 A inverse / the inverse of A 162
  • 163. 数学公式的读法(Pronunciation of mathematical expressions)5 函数(Functions) f(x) fx / f of x / the function f of x f : S→T a function f from S to T x maps to y / x is sent (or mapped) to y f(x) f prime x / f dash x / the (rst) derivative of f with respect to x f(x) f double–prime x / f double–dash x / the second derivative of f with respect to x f(x) f triple–prime x / f triple–dash x / the third derivative of f with respect to x f(4) four x / the fourth derivative of f with respect to x ln y log y to the base e / log to the base e of y / natural log (of) y 163
  • 164. 数学公式的读法(Pronunciation of mathematical expressions)5 函数(Functions) the partial (derivative) of f with respect to x1 the second partial (derivative) of f with respect to x1 the integral from zero to infinity the limit as x approaches zero from above 164
  • 165. Computer English Chapter 4 Data Structure
  • 166. Key points: useful terms and definitions of data structure Difficult points: Stack, queue, tree166
  • 167. Requirements:1. Three reasons for using data structures are efficiency, abstraction, and reusability. 2. The properties of Stack, Queue, and Tree3. 掌握常用英汉互译技巧 167
  • 168. New Words & Expressions: harsh table 杂凑(哈希)表 priority queues 优先队列 reusability n.复用性 binary tree 二叉树 traversing 遍历,走过 context-free 与上下文无关4.1 An Introduction to Data Structures 168
  • 169. Data comes in all shapes and sizes, but often it can be organized in the same way. For example, consider a list of things to do, a list of ingredients in a recipe, or a reading list for a class. Although each contains a different type of data, they all contain data organized in a similar way: a list. A list is one simple example of a data structure. Of course, there are many other common ways to organize data as well. In computing, some of the most common organizations are linked lists, stacks, queues, sets, hash tables, trees, heaps, priority queues, and graphs. Three reasons for using data structures are efficiency, abstraction, and reusability.数据以各种形状和大小出现,但是它常常可以用同样的方式来组织。例如,考虑要做事情的列表、处方成份的清单或一个班级的阅读目录。虽然它们包含不同类型的数据,但他们都包含以一种相似方式组织的数据:一个列表。列表是数据结构的一个简单例子。当然,还有许多其他组织数据通用方法。在计算机技术中,一些最常用的组织方式是链接表、堆栈、队列、集合、哈希表、树、堆、优先队列和图。使用数据结构的三个原因是效率、抽象性和复用性。4.1 An Introduction to Data Structures 169
  • 170. Efficiency Data structures organize data in ways that make algorithms more efficient. For example, consider some of the ways we can organize data for searching it. One simplistic approach is to place the data in an array and search the data by traversing element by element until the desired element is found. However, this method is inefficient because in many cases we end up traversing every element. By using another type of data structure, such as a hash table or a binary tree we can search the data considerably faster.效率 数据结构使用令算法更有效率的方法组织数据。例如,考虑一些我们用来查找数据的组织方式。一种过分简单的方式是将数据放置到数组中,并用遍历的方法找到需要的元素。然而,这种方法是低效率的,因为在许多情况下,我们需要遍历所有元素才能完成。使用其他类型的数据结构,如哈希表和二叉数,我们能够相当快速地搜寻数据。4.1 An Introduction to Data Structures 170
  • 171. Abstraction Data structures provide a more understandable way to look at data; thus, they offer a level of abstraction in solving problems. For example, by storing data in a stack, we can focus on things that we do with stacks, such as pushing and popping elements, rather than the details of how to implement each operation. In other words, data structures let us talk about programs in a less programmatic way.抽象化 数据结构提供一个更好理解的方法查看数据;因此,它们在解决问题中提供一定的抽象化水平。例如,通过把数据储存在堆栈中,我们可以将重点集中在对堆栈的操作上,如使元素进栈和出栈,而不是集中在实现操作的细节上。换句话说,数据结构使我们以较少的编程方式谈论程序。4.1 An Introduction to Data Structures 171
  • 172. Reusability Data structures are reusable because they tend to be modular and context-free. They are modular because each has a prescribed interface through which access to data stored in the data structure is restricted. That is, we access the data using only those operations the interface defines. Data structures are context-free because they can be used with any type of data and in a variety of situations or contexts. In C, we make a data structure store data of any type by using void pointers to the data rather than by maintaining private copies of the data in the data structure itself.复用性:因为数据结构趋向于模块化并和环境无关,所以数据结构是可以复用的。因为每种结构有一个预定的接口,通过该接口限制访问存储在数据结构中的数据,所以它们是模块化的。也就是说,我们只能使用接口定义的那些操作来访问数据。因为数据结构能用于任何类型的数据,并用于多种环境中,所以数据结构与使用环境无关。在C语言中,我们通过使用空指针,而不是通过维护非公开的数据备份,使数据结构存储任何类型的数据。4.1 An Introduction to Data Structures 172
  • 173. New Words & Expressions inviting adj.引人动心的 contiguous adj.邻近的, 接近的 stack n. 堆栈 insertion n.插入 deletion n.删除, 删除部分 pop 退栈 push 进栈 backtrack v.回溯 pseudocode n.[计]伪代码 retrieve v.重新得到;n.找回 pointer n.指针 pertinent adj.有关的, 相干的, 中肯的 extract vt. 取,引 back out 返回 entail vt. 使承担, 带来 traverse v.遍历 shrink v.收缩 allot vt.分配,充当,依靠 predecessor n.前辈, 前任 back and forth adv.来来往往地, 来回地 vacancy n.空, 空白, 空缺 stuff vt.填充, 塞满 Abbreviations LIFO (last-in, first-out) 后进先出 FIFO (first-in, first-out) 先进先出4.2 Stacks 173
  • 174. One of the properties of a list that makes a linked structure more inviting than a contiguous one is the need to insert and delete entries inside the list. Recall that it was such operations that had the potential of forcing the massive movement of names to fill or create holes in the case of a contiguous list. If we restrict such operations to the ends of the structure, we find that the use of a contiguous structure becomes a more convenient system. An example of this phenomenon is a stack, which is a list in which all insertions and deletions are performed at the same end of the structure. A consequence of this restriction is that the last entry entered will always be the first entry removed--an observation that leads to stacks being known as last-in, first-out (LIFO) structures.插入和删除记录的需求是使链接表结构比邻接表结构更诱人的原因之一。让我们回想一下在邻接表中具有填补和创建存储空缺能力的操作。如果我们限制这种操作只可以在结构的尾部进行,则邻接表就是一种比较方便的系统。这种现象的一个例子就是堆栈。在堆栈中,插入和删除操作都在结构的相同末端进行。如此限制的结果就是最后一个进入表的记录也就是第一个从表中删除的记录。这种结构称为后进先出结构。4.2 Stacks 174
  • 175. The end of a stack at which entries are inserted and deleted is called the top of the stack. The other end is sometimes called the stack's base. To reflect the fact that access to a stack is restricted to the topmost entry, we use special terminology when referring to the insertion and deletion operations. The process of inserting an object on the stack is called a push operation, and the process of deleting an object is called a pop operation. Thus we speak of pushing an entry onto a stack and popping an entry off a stack.堆栈尾部可以进行插入和删除操作的记录称为堆栈的栈顶,另一端叫做栈底。为了表示如何限制堆栈只能从栈顶访问,我们用一种特殊的术语来表示插入和删除操作。把一个对象插入堆栈的操作称为进栈操作,而从堆栈中删除一个对象的操作称为出栈操作,所以我们常说将一个条目进栈或者将其出栈。4.2 Stacks 175
  • 176. Backtracking A classic application of a stack involves the execution of a program involving procedures as found in our pseudocode. When the execution of a procedure is requested, the machine must transfer its attention to the procedure; yet later, when the procedure is completed, the machine must return to the original location before continuing. This means that, when the initial transfer is made, there must be a mechanism for remembering the location to which execution ultimately returns.回溯 堆栈的一个典型应用发生在一个程序单元调用一个过程的操作中。为了完成这个调用,机器必须将它的注意力转移到这个过程上;当过程调用结束后,机器必须返回到程序块进行调用时所处的位置。这就意味着必须有一种用来记录操作结束后返回的位置的机制。4.2 Stacks 176
  • 177. The situation is complicated by the fact that the procedure may itself request the execution of another procedure, which may request still another, and so on (Figure 7.9). Consequently, the return locations being remembered begin to pile up. Later, as each of these procedures is completed, execution must be returned to the proper place within the program unit that called the completed procedure. A system is therefore needed to save the return locations and later retrieve them in the proper order. 如果一个被调用的过程本身还要调用其他过程,而那些过程同样也需要调用另外的过程,这样一来整个情形就会很复杂。因此,返回地址的记忆就开始堆积。然后,当每一个过程都结束后,操作必须返回到被称为完成过程的程序块中的合适位置。因此,系统需要按照适当的顺序存储和找回返回地址。4.2 Stacks 177
  • 178. A stack is an ideal structure for such a system. As each procedure is called, a pointer to the pertinent return Location is pushed on a stack, and as each procedure is completed, the top entry from the stack is extracted with the assurance of obtaining a pointer to the proper return location. This example is representative of stack applications in general in that it demonstrates the relationship between stacks and the process of backtracking. Indeed, the concept of a stack is inherent in any process that entails backing out of a system in the opposite order from which it was entered.堆栈是满足这种需要的理想结构。当一个过程被调用时,将指向返回地址的指针进栈。然后,当一个过程完成时,将栈顶条目出栈,程序就可以准确得到返回地址。这是应用栈的一个典型例子,它表明了栈和回溯过程的关系。在任何可以从进入端反向返回系统的过程中,堆栈的概念是与生俱来的。4.2 Stacks 178
  • 179. As another example of backtracking, suppose we want to print the names in a linked list in reverse order--that is, last name first. Our problem is that the only way we can access the names is by following the linked structure. Thus we need a way of holding each name retrieved until all of the names that follow have been retrieved and printed. Our solution is to traverse the list from its beginning to its end while pushing the names we find onto a stack. After reaching the end of the list, we print the names as we pop them off the stack. 我们在来举另一个例子,假设反向输出一张链接表中的姓名,也就是把最后一个名字第一个输出。问题是我们只能跟着链接结构访问姓名。因此,我们需要一种方式,通过这种方式,我们可以保持每一个姓名能被检索,直到排列在这个姓名之后的姓名被得到并输出。我们的方案是从链接表的开始顺序遍历到结尾,与此同时把每一个姓名按照遍历顺序进栈。当到达链接表的末尾后,我们通过出栈操作来输出姓名。4.2 Stacks 179
  • 180. Stack Implementation To implement a stack structure in a computer's memory, it is customary to reserve a block of contiguous memory cells large enough to accommodate the stack as it grows and shrinks. (Determining the size of this block can often be a critical decision. If too little room is reserved, the stack ultimately exceeds the allotted storage space; if too much room is reserved, memory space will be wasted.) One end of this block is designated as the stack's base. It is here that the first entry pushed on the stack is stored, with each additional entry being placed next to its predecessor as the stack grows toward the other end of the reserved block.栈的实现 为了在计算机存储中实现栈结构,一般采取的方法是保留一块足够容纳栈大小变化的内存单元。(通常来说,确定块的大小是一个很重要的任务。如果保留的空间过小,那么栈最后可能从所分配的存储空间中溢出;而如果保留的空间过大,又是一种浪费。)块的一端作为栈底,栈的第一条数据会被存储在这里,以后的条目被依次放置在它之后的存储单元中,也就是堆栈向另外一端增加。4.2 Stacks 180
  • 181. Thus, as entries are pushed and popped, the top of the stack moves back and forth within the reserved block of memory cells. A means is therefore needed to maintain a record of the location of the top entry. For this purpose, the address of the top entry is stored in an additional memory cell known as the stack pointer. That is, the stack pointer points to the top of the stack. 因此,在条目进栈和出栈的时候,栈顶的位置就在存储单元块中前后移动。为了保存这个位置的轨迹,栈顶条目的地址被存储在一个附加的存储单元中,这个附加的存储单元被被称为堆栈指针。也就是说,堆栈指针就是一个指向栈顶的指针。4.2 Stacks 181
  • 182. The complete system, as illustrated in Figure 4-1, works as follows: To push a new entry on the stack, we first adjust the stack pointer to point to the vacancy just beyond the top of the stack and then place the new entry at this location. To pop an entry from the stack, we read the data pointed to by the stack pointer and then adjust the pointer to point to the next entry down on the stack.一个完整的系统(如图4-1所示)是这样工作的:为了把一条新的数据压入堆栈,我们首先调整堆栈指针,使之指向当前栈顶之前的空白。然后将新的条目置于此处。为了将条目从堆栈中弹出,我们首先读出堆栈指针所指向的数据,然后调整此指针指向堆栈中的下一条数据所在的存储单元。4.2 Stacks 182
  • 183. As we observed in the case of lists, a programmer would probably find it advantageous to write procedures that perform these push and pop operations so that the stack could be used as an abstract tool. Note that these procedures should handle such special cases as attempts to pop entries from an empty stack and to push entries onto a full stack. In particular, a complete stack system would probably contain procedures for pushing entries, popping entries, testing for an empty stack, and testing for a full stack.同我们观察到表中的情况一样,程序员也可以将堆栈编写成一个可以进行进栈和出栈操作的抽象工具。注意,这些过程应该可以处理诸如试图从空栈中弹出数据,或者将数据压入一个已经填满的堆栈等特殊情况。所以一个完整的堆栈系统应该包括进栈、出栈、测试堆栈是否空或满的功能。4.2 Stacks 183
  • 184. A stack organized in a contiguous block of memory cells exhibits little difference between the conceptual structure and the actual structure in main memory. Suppose, however, that we cannot reserve a fixed block of memory and be assured that the stack will always fit. A solution is to implement the stack as a linked structure similar to that of a list. This avoids the limitations of restricting the stack to a fixed-size block, since it allows the entries in the stack to be stuffed into small pieces of available space anywhere in memory. In such a situation, the conceptual stack structure will be quite different from the actual arrangement of the data in memory.存储在存储单元连续块中的栈展现出主存储器中概念结构与实际之间的一定差异。假设我们不能预测栈的大小,我们就不能保留一个总能满足堆栈的固定大小的存储块。一种解决方法就是实现一种与表结构相似的链接结构栈。这种方法避免了将堆栈限定在一块固定块中的局限性,因为它允许将新的条目插入存储器中任何一块足够大的空闲空间中。在这种情况下,概念上的堆栈结构与其在存储器中实际的数据组织方式就大不相同了。 4.2 Stacks 184
  • 185. New Words & Expressions queue n.行列, 队列; vi.排队 cafeteria n.自助餐厅 rear n.后面, 背后, 后方 set aside 留出,拨出 head pointer 头指针 tail pointer 尾指针 crawl vi.& n. 爬行, 蠕动, 徐徐行进 egocentric adj.自我中心的 consumption n.消费, 消费量 side effect 副作用 migrate vi.移动, 移植; vt.使移居, 使移植 circular queue 循环队列 envision vt.想象, 预想 bridge vt.跨接,接通4.3 Queues185
  • 186. In contrast to a stack in which both insertions and deletions are performed at the same end, a queue is a list in which all insertions are performed at one end while all deletions are made at the other. We have already met this structure in relation to waiting lines, where we recognized it as being a first-in, first-out (FIFO) storage system. Actually, the concept of a queue is inherent in any system in which objects are served in the same order in which they arrive.4.3 Queues栈的插入与删除操作都是在表的相同端进行的。而与此不同,队列是插入和删除操作分别在两端进行的表。我们已经遇到过这种与等待队列相关的结构,在此种情况中,我们把它当作是一种先进先出的存储系统。实际上,在那些对象输入与输出顺序相同的系统中,队列的概念是与生俱来的。队列的结尾从等待队列的关联中得到名字。186
  • 187. The ends of a queue get their names from this waiting-line relationship. The end at which entries are removed is called the head (or sometimes the front) of the queue just as we say that the next person to be served in a cafeteria is at the head (or front) of the line. Similarly, the end of the queue at which new entries are added is called the tail (or rear).4.3 Queues结尾处,也就是条目被移出队列的地方,被称为队列的队首(有时候也称为队前),这就好像我们在快餐厅中下一个将点餐的顾客为一队的队首一样。同样,队列的尾部,也就是条目被添加的地方,被称为队尾(或者队后)。187
  • 188. We can implement a queue in a computer's memory within a block of contiguous cells in a way similar to our storage of a stack. Since we need to perform operations at both ends of the structure, we set aside two memory cells to use as pointers instead of just one, as we did for a stack. One of these pointers, called the head pointers keeps track of the head of the queue; the other, called the tail pointer, keeps track of the tail. 4.3 Queues我们可以像存储栈那样通过连续单元组成的存储块在计算机主存储器中实现队列。因为我们需要在此结构的两端都进行操作,我们分配出两个存储单元用来当作指针,而非栈中那样仅仅需要一个单元来存储指针。其中的一个指针被称为头指针,用来保持队列头的轨迹;另一个指针被称为尾指针,用来保持队尾的轨迹。188
  • 189. When the queue is empty, both of these pointers point to the same location. Each time an entry is inserted, it is placed in the location pointed to by the tail pointer and then the tail pointer is adjusted to point toward the next unused location. In this manner, the tail pointer is always pointing to the first vacancy at the tail of the queue. Removing an entry from the queue involves extracting the entry pointed to by the head pointer and then adjusting the head pointer to point toward the entry that followed the removed entry.4.3 Queues如果一个队列为空,那么两个指针应该指向相同的位置。每当新的条目被插入时,均会被置于尾指针所指向的位置,同时修改尾指针,使之指向下一个未使用的位置。这样,尾指针总是指向队尾后的第一空闲存储单元。将一条数据移出队列的操作包括将头指针指向的条目取出,同时调整头指针使之指向排在被移出条目之后的位置 。189
  • 190. A problem remains with the storage system as described thus far. If left unchecked, the queue crawls slowly through memory like a glacier, destroying any other data in its path (Figure 4.2). This movement is the result of the rather egocentric policy of inserting each new entry by merely placing it next to the previous one and repositioning the tail pointer accordingly. If we add enough entries, the tail of the queue ultimately extends all the way to the end of the machine's memory. 4.3 Queues以上描述的存储系统仍然存在着问题。如果剩余的存储器未被检查,队列会像冰河一样在存储器中增长,同时将在此道路上的所有其他数据破坏(如图所示)。造成这种移动的相当一部分原因在于插入新条目时使用的“利己”策略,即在插入是仅仅将新数据置于当前队尾之后,同时重置尾指针。如果我们添加足够的条目,那么队尾最后就会从计算机存储器中溢出。190
  • 191. This consumption of memory is not the result of the queue's size but is a side effect of the queue's access procedure. (A small yet active queue can easily require more of a machine's memory resources than a large, inactive one.) One solution to this memory space problem might be to move the entries in a queue forward as the leading ones are removed, in the same manner as people waiting to buy theater tickets step forward each time a person has been served. However, this mass movement of data would be very inefficient. What we need is a way of confining the queue to one area of memory without being forced to perform major rearrangements of data.4.3 Queues存储器的消耗问题并不是因队列的大小而生的,其真正原因在于队列的实现问题。(一个小而动态变化的队列比一个大而保持不变的队列需要更多的机器存储资源。)解决存储器空间问题的一个可能方法是:当最前面的条目被移出时,前移队列中的其他条目,就好像人们在购买戏票时所采用的方法一样,每当一个人买到票后,就前移一人。然而这种方法在计算机中运行的效率很低,因为它将需要对数据进行大量的移动。191
  • 192. A common solution is to set aside a block of memory for the queue, start the queue at one end of the block, and let the queue migrate toward the other end of the block. Then, when the tail of the queue reaches the end of the block, we merely start inserting additional entries back at the original end of the block, which by this time is vacant. Likewise, when the last entry in the block finally becomes the head of the queue and is removed, the head pointer is adjusted back to the beginning of the block where other entries are, by this time, waiting. In this manner, the queue chases itself around within the block rather than wandering off through memory.4.3 Queues用来在计算机中控制队列的最一般的方法是为队列分配一块存储器,从存储块的末端开始存储队列,并且让队列向另一端增长。然而当队尾到达块的末端,即队列为空时,我们开始将新的条目反向于末端的方向插入。同样,当队列的最后一条成为队头并被移出时,调整头指针回到块的开端,同时在此等待。在此方法下,队列在一块区域内循环而不会出现内存溢出情况。 192
  • 193. Such a technique results in an implementation that is called a circular queue because the effect is that of forming a loop out of the block of memory cells allotted to the queue. As far as the queue is concerned, the last cell in the block is adjacent to the first cell.4.3 Queues采用此技术的实现方法称为循环队列,因为分配给队列的一块存储单元组成了一个环。就一个队列而言,存储块的最后一个单元与它的第一个单元相邻。193
  • 194. Once again, we should recognize the difference between the conceptual structure envisioned by the user of a queue and the actual cyclic structure implemented in the machine's memory. As in the case of the previous structures, these differences are normally bridged by software. That is along with the collection of memory cells used for data storage, a queue implementation should include a collection of procedures that insert and remove entries from the queue as well as detect whether the queue is empty or full. 4.3 Queues我们应该再次认识到队列使用者使用的概念结构与实际在计算机存储器中实现的循环结构之间的差异。在前一个结构的例子中,这些差异通常是通过软件来衔接的。也就是说,连同存储数据需要的一组存储单元,队列的实现应该包括一组用来插入和移出队列条目和探测队列是否为空或满的过程函数。然后,开发软件其他单元的程序员可以通过这些方法来实现队列的插入和移出操作,而不用关心其在存储器中的实际实现。194
  • 195. 常用英汉互译技巧一、增译法 根据英汉两种语言不同的思维方式、语言习惯和表达方式,在翻译时增添一些词、短句或句子,以便更准确地表达出原文所包含的意义。这种方式多半用在汉译英里。 1、汉语无主句较多,而英语句子一般都要有主语,所以在翻译汉语无主句的时候,除了少数可用英语无主句、被动语态或“There be…”结构来翻译以外,一般都要根据语境补出主语,使句子完整。 2、英汉两种语言在名词、代词、连词、介词和冠词的使用方法上也存在很大差别。英语中代词使用频率较高,凡说到人的器官和归某人所有的或与某人有关的事物时,必须在前面加上物主代词。因此,在汉译英时需要增补物主代词,而在英译汉时又需要根据情况适当地删减。 3、英语词与词、词组与词组以及句子与句子的逻辑关系一般用连词来表示,而汉语则往往通过上下文和语序来表示这种关系。因此,在汉译英时常常需要增补连词。英语句子离不开介词和冠词。 4、在汉译英时还要注意增补一些原文中暗含而没有明言的词语和一些概括性、注释性的词语,以确保译文意思的完整。 195
  • 196. 常用英汉互译技巧一、增译法 例1. Indeed, the reverse is true 实际情况恰好相反。(增译名词) 例2. 这是这两代计算机之间的又一个共同点。 This is yet another common point between the computers of the two generations.(增译介词) 例3. Individual mathematicians often have their own way of pronouncing mathematical expressions and in many cases there is no generally accepted “correct” pronunciation. 每个数学家对数学公式常常有各自的读法,在许多情况下,并不存在一个普遍接受的所谓“正确”读法。(增加隐含意义的词) 例4. 只有在可能发生混淆、或要强调其观点时,数学家才使用较长的读法 It is only when confusion may occur, or where he/she wishes to emphasis the point, that the mathematician will use the longer forms. (增加主语) 196
  • 197. 常用英汉互译技巧二、省译法 这是与增译法相对应的一种翻译方法,即删去不符合目标语思维习惯、语言习惯和表达方式的词,以避免译文累赘。增译法的例句反之即可。又如: 例1. You will be staying in this hotel during your visit in Beijing. 你在北京访问期间就住在这家饭店里。(省译物主代词) 例2. I hope you will enjoy your stay here. 希望您在这儿过得愉快。(省译主语) 例3. 中国政府历来重视环境保护工作。 The Chinese government has always attached great importance to environmental protection. (省译名词) 例4. The development of IC made it possible for electronic devices to become smaller and smaller. 集成电路的发展是电子器件可以做得越来越小。(省译形式主语it) 197
  • 198. 常用英汉互译技巧三、转换法 在翻译过程中,为了使译文符合目标语的表述方式、方法和习惯,对原句中的词类、句型和语态等进行转换: 1、在词性方面,把名词转换为代词、形容词、动词;把动词转换成名词、形容词、副词、介词;把形容词转换成副词和短语。 2、在句子成分方面,把主语变成状语、定语、宾语、表语;把谓语变成主语、定语、表语;把定语变成状语、主语;把宾语变成主语。 3、在句型方面,把并列句变成复合句,把复合句变成并列句,把状语从句变成定语从句。 4、在语态方面,可以把主动语态变为被动语态。 198
  • 199. 常用英汉互译技巧三、转换法 例1. Too much exposure to TV programs will do great harm to the eyesight of children. 孩子们看电视过多会大大地损坏视力。(名词转动词) 例2. 由于我们实行了改革开放政策,我国的综合国力有了明显的增强。 Thanks to the introduction of our reform and opening policy, our comprehensive national strength has greatly improved. (动词转名词) 例3. 时间不早了,我们回去吧! We don’t have much time left. Let’s go back. (句型转换)199
  • 200. 常用英汉互译技巧四、拆句法和合并法 例1. Increased cooperation with China is in the interests of the United States. 同中国加强合作,符合美国的利益。(在主谓连接处拆译) 例3. 中国是个大国,百分之八十的人口从事农业,但耕地只占土地面积的十分之一,其余为山脉、森林、城镇和其他用地。 China is a large country with four-fifths of the population engaged in agriculture, but only one tenth of the land is farmland, the rest being mountains, forests and places for urban and other uses.(合译法) 例4. Packet switching is a method of slicing digital messages into parcels called “packets,” sending the packets along different communication paths as they become available, and then reassembling the packets once they arrive at their destination. 分组交换是传输数据的一种方法,它先将数据信息分割成许多称为“分组”的数据信息包;当路径可用时,经过不同的通信路径发送;当到达目的地后,再将它们组装起来。(将长定语从句拆成几个并列的分句)200
  • 201. 常用英汉互译技巧五、正译法和反译法 这两种方法通常用于汉译英,偶尔也用于英译汉。所谓正译,是指把句子按照与汉语相同的语序或表达方式译成英语。所谓反译则是指把句子按照与汉语相反的语序或表达方式译成英语。正译与反译常常具有同义的效果,但反译往往更符合英语的思维方式和表达习惯。因此比较地道 。 例1. 你可以从因特网上获得这一信息。 You can obtain this information on the Internet. (正译) This information is accessible/available on the Internet. (反译) 例2. 他突然想到了一个新主意。 Suddenly he had a new idea. (正译) He suddenly thought out a new idea. (正译) A new idea suddenly occurred to/struck him. (反译)201
  • 202. 常用英汉互译技巧六、倒置法 在汉语中,定语修饰语和状语修饰语往往位于被修饰语之前;在英语中,许多修饰语常常位于被修饰语之后,因此翻译时往往要把原文的语序颠倒过来。倒置法通常用于英译汉, 即对英语长句按照汉语的习惯表达法进行前后调换,按意群或进行全部倒置,原则是使汉语译句安排符合现代汉语论理叙事的一般逻辑顺序。有时倒置法也用于汉译英。如: 例1. At this moment, through the wonder of telecommunications, more people are seeing and hearing what we say than on any other occasions in the whole history of the world. 此时此刻,通过现代通信手段的奇迹,看到和听到我们讲话的人比整个世界历史上任何其他这样的场合都要多。(部分倒置) 例2. 改革开放以来,中国发生了巨大的变化。 Great changes have taken place in China since the introduction of the reform and opening policy.(全部倒置)202
  • 203. 常用英汉互译技巧七、包孕法 这种方法多用于英译汉。所谓包孕是指在把英语长句译成汉语时,把英语后置成分按照汉语的正常语序放在中心词之前,使修饰成分在汉语句中形成前置包孕。但修饰成分不宜过长,否则会形成拖沓或造成汉语句子成分在连接上的纠葛。如: 例1. IP multicasting is a set of technologies that enables efficient delivery of data to many locations on a network. IP多信道广播是使数据向网络中许多位置高效传送的一组技术。 例2. What brings us together is that we have common interests which transcend those differences. 使我们走到一起的,是我们有超越这些分歧的共同利益 203
  • 204. 常用英汉互译技巧八、插入法 指把难以处理的句子成分用破折号、括号或前后逗号插入译句中。这种方法主要用于笔译中。偶尔也用于口译中,即用同位语、插入语或定语从句来处理一些解释性成分。 如:如果说宣布收回香港就会像夫人说的“带来灾难性的影响”,那我们将勇敢地面对这个灾难,做出决策。 If the announcement of the recovery of Hong Kong would bring about, as Madam put it, “disastrous effects,” we will face that disaster squarely and make a new policy decision.204
  • 205. 常用英汉互译技巧九、重组法 在进行英译汉时,为了使译文流畅和更符合汉语叙事论理的习惯,在捋清英语长句的结构、弄懂英语原意的基础上,彻底摆脱原文语序和句子形式,对句子进行重新组合。 如:Decision must be made very rapidly; physical endurance is tested as much as perception, because an enormous amount of time must be spent making certain that the key figures act on the basis of the same information and purpose. 必须把大量时间花在确保关键人物均根据同一情报和目的行事,而这一切对身体的耐力和思维能力都是一大考验。因此,一旦考虑成熟,决策者就应迅速做出决策。205
  • 206. 常用英汉互译技巧十、综合法 指把难以处理的句子成分用破折号、括号或前后逗号插入译句中。这种方法主要用于笔译中。偶尔也用于口译中,即用同位语、插入语或定语从句来处理一些解释性成分。 如: 如果说宣布收回香港就会像夫人说的“带来灾难性的影响”,那我们将勇敢地面对这个灾难,做出决策。 If the announcement of the recovery of Hong Kong would bring about, as Madam put it, “disastrous effects,” we will face that disaster squarely and make a new policy decision.206
  • 207. 常用英汉互译技巧十、综合法 是指单用某种翻译技巧无法译出时,着眼篇章,以逻辑分析为基础,同时使用转换法、倒置法、增译法、省译法、拆句法等多种翻译技巧的方法。 如: Behind this formal definition are three extremely important concepts that are the basis for understanding the Internet: packet switching, the TCP/IP communications protocol, and client/server computing. 在这个正式的定义背后,隐含着三个极其重要的概念:分组交换、TCP/IP(传输控制协议/网际协议)通信协议和客户机/服务器计算技术,它们乃是理解因特网的基础。207
  • 208. Computer English Chapter 4 Data Structure
  • 209. Key points: Function and structure of Operating System Difficult points: Resource allocation and related functions User interface functions 209
  • 210. Requirements:1. 了解操作系统是如何实现资源分配和用户接口功能的。 2. 通过学习操作系统功能的演化,认识操作系统在实现过程中采用的基本概念与技术,了解操作系统设计中的概念。3. 认识操作系统的结构,了解当前常见操作系统的特点4. 掌握被动语态的翻译技巧。210
  • 211. New Words & Expressions: OS (Operating System) 操作系统 binding n. 捆绑 mutual interference 相互干扰 interface n.界面,接口 facilitate vt. 推动, 帮助,促进 allocation n.分配, 安置 constraint n.约束, 强制, 局促 criteria n.标准 embody vt.具体表达, 使具体化 entry n. 条目,登录 privilege n.特权; vt.给与...特权 partition vt.分区 approach n. 方法, 途径 a priori 预先,事前 perceive v.感知, 感到, 认识到 preemption n.抢占 suboptimal adj.未达最佳标准的 entrust v.委托 sequential adj. 顺序的,串行的 exclusive use 专用 concurrent adj.并发的, 并行的 de-allocate vt. 释放 scheduling n.调度 salient features 特征, 特色 initiate vt. vi. 开始, 发动5.1 OS Function 211
  • 212. OS functions can be classified into Resource allocation and related functions User interface functions. The resource allocation function implements resource sharing by the users of a computer system. Basically, it performs binding of a set of resources with a requesting program, that is, it associates resources with a program. The related functions implement protection of users sharing a set of resources against mutual interference.操作系统的功能可分为: 1. 资源分配及相关功能。 2. 用户接口功能 资源分配功能负责实现计算机系统的用户共享资源。它主要将资源和提出需求的程序绑定在一起,即使资源和程序相关联。与之相关的一些功能实现不同用户在共享资源时的保护,以免发生相互干扰。5.1 OS Function 212
  • 213. The user interface function facilitates creation and use of appropriate computational structures by a user. This function typically involves the use of a command language or a menu.用户接口功帮助用户创立并使用适当的计算结构,这一功能通常涉及命令、语言或菜单的应用。5.1 OS Function 213
  • 214. The resource allocation function allocates resources for use by a user's computation. Resources can be divided into system provided resources like CPUs, memory areas and IO devices, or user-created resources like files which are entrusted to the OS. 资源分配功能分配资源供用户计算使用。资源可分为系统提供的资源(如CPU、存储器区域及I/O设备群)和用户创建的资源(如由操作系统管理的文件等)。5.1.1 Resource allocation and related functions 214
  • 215. Resource allocation criteria depend on whether a resource is a system resource or a user-created resource. Allocation of system resources is driven by considerations of efficiency of resource utilization. Allocation of user-created resources is based on a set of constraints specified by its creator and typically embodies the notion of access privileges.资源分配的标准根据资源的分类确定,系统资源的分配要考虑资源利用的效率,而用户创立资源的分配则基于该资源的创立者所设定的特种限制,比如访问权限。5.1.1 Resource allocation and related functions 215
  • 216. Two popular strategies for resource allocation are: Partitioning of resources Allocation from a pool资源分配通常采取以下两种策略; 1. 资源分区。 2. 从资源池中分配。5.1.1 Resource allocation and related functions 216
  • 217. In the resource partitioning approach, the OS decides a priori what resources should be allocated to a user computation. This approach is called static allocation because the allocation is made before the execution of a program starts. Static resource allocation is simple to implement, however, it could lead to suboptimal utilization because the allocation is made on the basis of perceived needs of a program, rather than its actual needs. 在资源分区方式中,操作系统预先决定把哪些资源分配给某个用户计算使用,这种方法也称为静态分配,因为分配是在程序执行前进行的。静态资源分配易于实现,但由于它不是从程序的实际需要出发,而是根据程序预先提出的需求来做决定,所以容易导致系统利用率下降。5.1.1 Resource allocation and related functions 217
  • 218. In the latter approach, the OS maintains a common pool of resources and allocates from this pool on a need basis. Thus, OS considers allocation of a resource when a program raises a request for a resource. This approach is called dynamic allocation because the allocation takes place during the execution of a program. Dynamic resource allocation can lead to better utilization of resources because the allocation is made when a program requests a resource.在后一种分配方式中,操作系统维护一个公共资源池,并按照程序的需要对资源进行分配。这样,OS只在程序提出对一个资源的需求时才进行资源分配,这种方式也称为动态分配,因为分配是在程序执行的过程中进行的。动态存储分配的资源利用率较高,因为它是在程序需要资源时才进行分配。5.1.1 Resource allocation and related functions 218
  • 219. An OS can use a resource table as the central data structure allocation. The table contains an entry for each resource unit in the system. The entry contains the name or address of the resource unit and its present status, i.e. whether it is free or allocated to some program. When a program raises a request for a resource, the resource would be allocated to it if it is presently free. If many resource units of a resource class exist in the system, a resource request only indicates the resource class and the OS checks if any resource unit of that class is available for allocation.操作系统可以利用资源表作为资源分配的中心数据结构。表中包含系统的每一资源单位项数据项中记录资源单位的名称或地址以及当前状态,即它是空闲的还是己经分配给某一程序。当程序对某一资源提出请求后,若该资源是空闲的,则它将被分配给那个程序。若系统中同一资源类中存在许多资源单位,程序的资源请求只指明要求哪类资源而由操作系统检查该类中是否有可用的资源单位可以分配。5.1.1 Resource allocation and related functions 219
  • 220. In the partitioned resource allocation approach, the OS decides on the resources to be allocated to a program based on the number of resources and the number of programs in the system. For example, an OS may decide that a program can be allocated 1 MB of memory, 2000 disk blocks and a monitor. Such a collection of resources is referred to as a partition. In effect, a set of partitions can be predefined in the system. The resource table can have an entry for each resource partition. When a new program is to be started, an available partition is allocated to it.在资源分区分配中,操作系统依据系统中的资源数目和程序数目决定如何进行资源分配。例如,操作系统可能会决定一个程序可以使用1MB内存、20O0个磁盘块及1个监视器,这一系列资源可以作为一个分区。系统可以提前定义出一系列这样的区,资源表中为每一资源区保存相应的数据项。当新的程序开始时将分配给它一个可用的分区。5.1.1 Resource allocation and related functions 220
  • 221. Resource preemption There are different ways in which resource can be shared by a set of programs. Some of these are: Sequential sharing Concurrent sharing资源抢占 资源被一系列程序分享可以有多种不同的方式,如: 串行共享 并行共亨5.1.1 Resource allocation and related functions 221
  • 222. In sequential sharing, a resource is allocated for exclusive use by a program. When the resource is de-allocated, it is marked free in the resource table. Now it can be allocated to another program. In concurrent sharing, two or more programs can concurrently use the same resource. Examples of concurrent sharing are data files. Most other resources cannot be shared concurrently. Unless otherwise mentioned, all through this text resources are assumed to be only sequentially shareable.在串行共享中,一个资源只能分配给一个程序,当资源被释放后,它在资源表中被标记为“空闲”,这时它才能被分配给下一个程序。在并行共亨中,两个以上的程序可以同时使用同样的资源。并行共享的例子是数据文件,其他资源通常不能被并行共享。在本文中以后若无特殊说明,所有资源都被假设为只能串行共享。5.1.1 Resource allocation and related functions 222
  • 223. When a resource is sequentially shareable, the system can de-allocate a resource when the program makes an explicit request for de-allocation. Alternatively, it can de-allocate a resource by force. This is called resource preemption, that is, forceful de-allocation of a resource.当资源可以串行共享时,系统可以在程序明确地提出释放分配的请求后,对资源进行释放。或者,系统也可强行释放资源,这称为资源抢占。5.1.1 Resource allocation and related functions 223
  • 224. Preemption of system resources is used by the OS to enforce fairness in their use by programs, or to realize certain system level goals. A preempted program cannot execute unless the preempted resource unit, or some other resource unit pi' the same resource class, is allocated to it once again. The shorter term preemption is used preemption of the CPU, and the full term resource preemption is used for preemption of other resources.资源抢占是能指强行释放资源。操作系统依靠对系统资源的抢占确保程序对资源的平等利用,或实现一些系统级的目标。对于资源被抢占的程序来说,除非把被抢占的资源单位或同一资源类的其他资源单位重新分配给它,否则无法继续执行。我们称抢占CPU为抢占,而称抢占其他资源为资源抢占。5.1.1 Resource allocation and related functions 224
  • 225. CPU sharing The CPU can be shared in a sequential manner only. Hence only one program can execute at any time. Other programs in the system have to wait their turn. It is often important to provide fair service to all programs in the system. Hence preemption is used to free the CPU so that it can be given to another program. Deciding which program should be given the CPU and for how long is a critical function. This function is called CPU Scheduling, or simply scheduling. Partitioning is a bad approach for CPU Sharing, allocation from a pool is the obvious approach to use.CPU共享 CPU只能串行共享,因此它一次只能执行一个程序,其他程序必须依次等待。通常情况下,系统会要求平等对待所有的程序,用抢占来释放CPU以执行其他程序。因此决定该执行哪个程序并执行多长时间是一个十分重要的功能,这一功能被称为CPU调度或简称调度。显然,资源分区不适用于CPU共享,同此,从资源池中分配成为惟一的选择。5.1.1 Resource allocation and related functions 225
  • 226. Memory sharing Like the CPU, the memory also cannot be shared concurrently. However, unlike the CPU, its availability can be increased by treating different parts of memory as different resources. Both the partitioning and the pool-based allocation approaches can be used to manage the memory resource. Memory preemption can also be used to increase the availability of memory to programs. Special terms are used for different memory preemption techniques, hence the term “memory preemption” is rarely used in our discussions.存储器共享 和 CPU一样,存储器也不能并行共享。但与CPU不同的是,可以把存储器的不同部份看作不同的资源,因此可以增加它的可用性。资源分区和基于资源池的分配方式都适用于存储器资源管理。存储器抢占也可用于提高程序对存储器的可用性,但由于对不同的存储器抢占技术都有专用术语,故在本书很少使用“存储器抢占”的说法。5.1.1 Resource allocation and related functions 226
  • 227. The purpose of a user interface is to provide for the use of OS resources, primarily the CPU, for processing a user's computational requirements. OS user interfaces typically use command languages. The user uses a command to set up an appropriate computational structure to fulfill a computational requirement.用户接口的目的是为用户提供使用操作系统资源(主要是CPU)的接口来完成用户的计算请求。操作系统用户接口一般使命令语言,用户通过命令建方合适的计算结构以满足计算要求。5.1.2 User interface related functions 227
  • 228. A variety of computational structures can be defined by an OS. A sample list of computational structures is as follows: 1. A single program 2. A sequence of single programs 3. A collection of programs.不同的计算结构可由操作系统决定。计算结构举例如下: 1. 单一程序 2. 单一程序的序列 3. 程序集合5.1.2 User interface related functions 228
  • 229. These computational structures will be defined and described in later chapters; here we only point out a few salient features. It is assumed that each program is individually initiated by the user through the user interface. The single program consists of the execution of a program on a given set of data. The user initiates execution of the program through a command. Two kinds of programs can exist sequential and concurrent. A sequential program, which matches with the conventional notion of a program, is the simplest computational structure. 以上这些计算结构将在以后各章中定义和描述,此处只指出一些简单的特征。例如每个程序都是由用户通过用户接口分别进行初始化的,单一程序是由在给定的数据集上的一个程序执行组成的,用户通过命令启动程序。程序可以分为两种:顺序的和并发的。顺序程序符合传统的程序概念,是最简单的计算结构。5.1.2 User interface related functions 229
  • 230. In a concurrent program, different parts of the program can execute concurrently. For this, the OS has to be aware the identities of the different parts which can execute concurrently. This function is typically not served by the user interface of the OS. In this chapter it is assumed that each program is sequential in nature.而在并发程序中,程序的不同部分可被同时执行。为此,操作系统需要了解这些可以同时执行的不同部分的实体,操作系统的用户接口通常不支持这一功能。在本章中,假设所有的程序都是顺序执行的。5.1.2 User interface related functions 230
  • 231. In a sequence of programs, each program is initiated by the user individually. However, the programs are not independent of each other---executing of a program is meaningful only if the previous programs in the sequence execute successfully. However, since the programs are initiated individually, their interface with one another is set up explicitly by the user. 在一个程序序列中,每个程序是由用户单独启动的,但程序之间并非相互独立,只有当前一程序执行成功后,下一个程序的执行才有意义,但由于程序是独立启动的,它们之间相互的接口由用户明确设定。5.1.2 User interface related functions 231
  • 232. In a collection of programs, the user names the programs involved in the collection in his command. Thus, their identities are indicated to the OS through the user interface itself. The interface between the programs is handled by the OS.在程序集合中,用户在其命令中为集合中涉及的程序命名。由此它们将通过用户接口被操作系统识别,程序间的接口由操作系统处理。5.1.2 User interface related functions 232
  • 233. New Words & Expressions: inherent adj.固有的, 内在的, 与生俱来的 execute vt.执行, 实行, 完成 Pascal n.〈计〉PASCAL语言 compilation n.编辑, 汇编 bat abbr.[计] 批处理文件的扩展名 script n.脚本,UNIX(命令)过程5.2 Evolution of OS Function 233
  • 234. Operating system (OS) functions have evolved in response to the following considerations and issues: 1. Efficient utilization of computing resources 2. New features in computer architecture 3. New user requirements.操作系统的功能因为以下一些原因而不断演化: 1. 计算资源的有效应用。 2. 计算机结构的新特性。 3. 新的用户需求。5.2 Evolution of OS Function 234
  • 235. Different operating systems address these issues in different manner, however most operating systems contain components which have similar functionalities. For example, all operating systems contain components for functions of memory management, process management and protection of users from one another. The techniques used to implement these functions may vary from one OS to another, but the fundamental concepts are the same. 不同操作系统采取不同的方法处理这些问题,但几乎所有的操作系统都拥有一些功能相似的部分,如存储器管理、进程管理和用户保护。尽管不同的操作系统采取的具体技术不同,但其基本概念是一致的。由于它们之间的相似性才使我们可以对其进行研究。因此,只需学习操作系统设计的基本概念及一些操作系统实现的实例,即可了解操作系统原理,而不用学习大量的操作系统。5.2 Evolution of OS Function 235
  • 236. In this chapter we study the concepts in OS design by studying the evolution of OS functions and identifying the fundamental concepts and techniques used in their implementation. We also introduce formal definitions of concepts and relevant terminology.本章我们将通过学习操作系统功能的演化和认识操作系统在实现过程中采用的基本概念与技术,了解操作系统设计中的概念,还将介绍一些概念和相关术语的正式定义。 5.2 Evolution of OS Function 236
  • 237. Jobs, programs and processes The primary function of an OS is to organize the execution of user computations in a computer system. A suitable characterization of user computations is therefore fundamental to its design. Three characterizations of user computations have been used to date--jobs, programs and processes. 作业、程序和进程 操作系统的基本功能是在计算机系统中组织用户计算的执行。因此它在设计中要求对用户计算有恰当的特征描述。通常在用户计算中使用以下三种特征记述——作业、程序和进程。5.2 Evolution of OS Function 237
  • 238. Jobs, programs and processes A program is the classical view of a computation. It consists of a set of program units, including program units obtained from libraries, which constitute an object code to be executed. A process is an execution of a program or of a part of a program. It differs from a program when concurrent programming techniques are used for coding the program. In such a case many processes can execute a program or a part of a program.程序是计算的传统观点,它由一系列程序单元构成,包括从库中获取的程序单元,并组成可执行的目标代码。进程是一个程序或一个程序部分的一次执行。在应用并行编码技术时,许多进程可以执行同一程序或其一部分,这时进程与程序是不同的。5.2 Evolution of OS Function 238
  • 239. Jobs, programs and processes A job is a computational structure which is a sequence of programs. It consists of a sequence of job steps, each job step constituting the execution of a program. Thus, a job for the compilation and execution of a Pascal program involves the following three job steps---execution of the Pascal compiler to compile the Pascal program, execution of the linker to prepare the compiled program for execution and execution of the object program which has just been linked. 作业是一个程序序列的计算结构。它由一系列作业步组成,每一步都是一个程序执行的一部分。例如,一个对Pascal程序进行编译和执行的作业包括以下三步:用编译程序对程序进行编译,用链接程序准备对编译好的程序的执行,以及执行刚刚链接好的目标程序。5.2 Evolution of OS Function 239
  • 240. Jobs, programs and processes Note that it is not meaningful to execute a job step unless each of the previous job steps has executed success fully, e.g. linking is not meaningful unless compilation was successful. The notion of a job was important in early computer systems which did not support interactive computing it is of marginal relevance in most contemporary systems, for example the BAT files of MS DOS and shell scripts of Unix resemble the notion of jobs. 每一步都要在前一步执行成功后才能执行。比如,除非编译成功,否则链接就毫无意义。在早期不支持交互计算的计算机系统中,作业的概念很重要。它在现代系统中也有应用,如MS-DOS中的Bat文件和Unix中的shell脚本。5.2 Evolution of OS Function 240
  • 241. New Words & Expressions interrupt vt.& n.中断 bulk n. 成批,大量,整体 monolithic adj.整体式的,一致的;n.单片 share vt.& n.共享 segregate v.隔离 interact vi.互相作用, 互相影响 kernel n.核心,内核 invoke v.调用 process scheduling 过程调度 virtual adj.虚拟的 interprocess adj.进程间的 recovery n.恢复 initiation n.开始,初始化 microkernel n.微核 portability n.可移植性 extensibility n.可延长性, 展开性 stratify vt. 分层,层化 hierarchy n.层次,层级 detract v.转移 devise vt.设计, 发明, 图谋, 作出 not-so-small 并不十分小 real time 实时 interpretation n.解释, 阐明, 口译, 通译 QNX 一种操作系统 Mach 一种采用微内核技术的UNIX操作系统 5.3 OS Structure 241
  • 242. OS design strongly depends on two factors: architectural features of the computer on which it operates, and features of its application domain. Dependence on architectural features is caused by the need to exercise complete control over all functional units of the system. Hence, the OS needs to know the addressing structure, interrupt structure, IO organization and memory protection features of the computer system. 操作系统的设计主要基于以下两个因素:它所操作的计算机的结构特征及它的应用域特征。对结构特征的依赖是由对系统的所有功能单位进行完全控制的需要而产生的。因此,操作系统需要了解计算机系统的地址结构、中断结构、I/O体系结构及存储器保护特性。5.3 OS Structure 242
  • 243. OS policies typically depend on its application domain. For example, the CPU scheduling policy depends on whether the OS will be used for time sharing, or for real time applications. The dependence on these two factors poses obvious difficulties in using an OS on computers with different architectures and different application domains.操作系统的策略通常由它的应用域决定:例如,CPU的调度策略是由操作系统是用于分时应用还是实时应用来决定。对这两方面因素的依赖导致在不同应用域中的不同结构的计算机上使用同一操作系统的巨大困难。5.3 OS Structure 243
  • 244. Consider the development of an OS for a similar application domain on two computer systems Cl and C2. These two OSs differ in terms of architecture specific OS code. Remainder of the code, which forms the bulk of the total OS code, does not have any architectural dependencies. 考虑设计一个操作系统,使它能应用于在相似的应用域中的两个计算机系统C1和C2上。下面的两个操作系统与结构相关的操作系统代码有所不同,其余的大部分操作系统代码都与结构无关。5.3 OS Structure 244
  • 245. It would be tempting to consider development of the OS for cl and c2 in the following manner: 1. Develop the OS for computer system Cl. Let this be called OS1. 2. Modify OS1 to obtain the OS for computer system C2, i.e. OS2. That is, OS2 is obtained by porting OS1 to C2.则可以考虑采用以下方式开发用于Cl和C2的操作系统: 1. 设计用于计算机系统Cl的操作系统,设其为OS1。 2. 把OS1修改为能在计算机系统C2上使用的操作系统, 也就是说,OS2是通过把OS1移植到C2上得到的。5.3 OS Structure 245
  • 246. In early operating systems, this approach faced several difficulties due to the monolithic structure of the OS. Thus, OSs did not provide clean interfaces between the architecture specific and architecture independent parts of their code. Hence the total porting effort was determined by the total size of OS code, rather than by the size of its architecture specific part. Historically, this difficulty has been addressed by developing an OS structure which separates the architecture specific and architecture size of its architecture specific parts of an OS. 由于早期的操作系统均是整体结构,这就给这种方式的实施造成了困难。因为操作系统并没有为结构相关的及结构无关的代码之间提供正确的接口,因此移植工作就要涉及全部的操作系统代码,而不是其中只和结构相关的部分。历史上,这一困难是通过设计一种把结构相关的部分与结构无关的部分分开的操作系统结构来克服的。5.3 OS Structure 246
  • 247. This enables OSs for different computer systems to share much of their design. When OSs are coded in a high level language, this even permits code sharing across OSs. To see how the separation of architecture specific and architecture independent parts can be implemented, consider the nature of a typical OS component. The component governs a class of resources, e.g. the processor(s) of the computer system, its memory, etc. Resource control actions of the module can be classified into 1. Policies governing the use of resources. 2. Mechanisms to implement the policy.这样可以使不同计算机系统的操作系统分享大部分的设计。若操作系统是用高级语言编写的,则不同的操作系统之间甚至可以共享代码。为理解与结构相关的部分和与结构无关的部分是如何分开的,我们考虑一下一个典型操作系统组件的特性。每个组件都管理一类资源,如引算机的处理器和存储器等。模块的资源控制动作可以分为: 1. 控制资源使用的策略。 2. 执行策略的机制。5.3 OS Structure 247
  • 248. Policies are usually architecture independent, while mechanisms are often architecture dependent. Hence the policy routines and mechanisms should be segregated to achieve separation of the architecture specific and architecture independent parts of OS. Figure 5-1 shows an OS structure which separates the architecture specific and architecture independent parts into two modules. 策略通常是与结构无关的,而机制通常是与结构相关的。因此,为使与结构相关的部分和与结构无关的部分分开,策略例程序与机制分开。图5-1显示了一个把与结构相关的部分及与结构无关的部分分成两个模块的操作系统结构。5.3 OS Structure 248
  • 249. The module containing the policy routines is architecture independent and the part containing the mechanisms is architecture specific. The policy routines invoke the mechanisms as and when necessary. Such an OS can be ported to a new computer system by rewriting the mechanisms module for the new system, and integrating it with the policy module.包含策略例程的模块是与结构无关的,而包含机制的模块是与结构相关的,策略例程只在必要的情况下才使用机制。这样的操作系统只重写机制模块就可以与策略模块结合,移植到新的系统上。5.3 OS Structure 249
  • 250. The structuring principle shown in Fig.5-1 is implemented using the layered organization shown in Fig.5-2 which is based on the notion of extended machines. Each software layer enhances the capabilities of the architecture by adding new features. In effect, it elevates the architectural interface closer to the user interface. For example, the lowest layer offers a machine which has in-built mechanisms for scheduling, memory management and I/O control. This simplifies the functioning of the layer above it. 图5-1所示的结构原理是由图5-2所示的基于扩展机概念的分层结构实现的。每个软件层都通过添加新特性来扩展结构的性能。实际上,这使得结构接口更接近于用户端口。例如最底层提供了一个内置的调度、存储器管理及I/O控制机制的机器,这就简化了上面各层的功能。5.3 OS Structure 250
  • 251. Fig.5-1 Structure of an OS Fig. 5-2 OS layers251
  • 252. Each layer only communicates with the adjoining layers through well defined interfaces. Thus, a user command may percolate through the layers to reach the lowest layer which directly interacts with the architecture. This layer is called the OS kernel. Many modem OSs, particularly Unix, use such OS structure. The porting effort of such an OS is determined by the size of the OS kernel.每层只需通过定义好的接口与相邻的层通信。因此,用户的指令可以透过各层直接达到与结构直接交互的最底层,这一层又称为操作系统内核。许多现代的操作系统,特别是Unix,都使用这种结构。这种操作系统的移植难度大小只由系统内核的大小决定。5.3 OS Structure 252
  • 253. OS kernel The typical mechanisms contained in the OS kernel are listed in Table 5-1. The kernel gets control when 1. An exceptional situation arises in the system. 2. An OS policy module explicitly invokes a kernel mechanism.操作系统内核 系统内核中包含的一般机制在表5-1中列出,内核在下列情况下获得控制权: 1. 系统小出现异常情况, 2. 一个操作系统策略模块明确地激活一个内核机制。5.3 OS Structure 253
  • 254. OS kernel In the former case, the entry is through the interrupt processing mechanism which senses the occurrence of a hardware interrupt. In the latter case, the OS policy module typically transfers control to the kernel through a software interrupt. Thus, in either case the entry to the kernel is through the interrupt processing mechanism. For this reason, the OS kernel is often said to be interrupt-driven.在前一种情况下,控制是通过一个负责感知硬件中断的中断处理机制传递的。在后一种情况下,操作系统的策略模块通常会通过—个软件中断来把控制交给内核。因此,无论在哪种情况下都是通过中断处理机制进入内核。因此,系统内核常被称为“中断驱动的”。5.3 OS Structure 254
  • 255. OS kernel Many well-known OS kernels include functionalities not shown in Table 5-1, for example, process scheduling, device drivers, core file system services and certain memory management functions. This simplifies the writing of non-kernel software. However, it tends to detract from the porting advantages of the kernel based OS structure.许多著名操作系统的内核包含一些并未在表5-1中列出的功能。如过程调度、设备驱动程序、核心文件系统服务及一些存储器管理功能。这样可以简化非内核软件的编程,但也削弱了基于内核的操作系统结构的移植优势。5.3 OS Structure 255
  • 256. OS microkernels The notion of microkernels was developed in the early 1990's to enhance the portability, extensibility and reliability of operating systems. The primary motivation for a microkernel arises from disadvantages of the layered OS model based on kernels. The main problem with the layered model is that every OS functionality is stratified into a hierarchy of layers. Thus, every part of the functionality is subject to the constraints imposed by the interface of the OS layer to which it belongs.操作系统微内核 微内核的概念是在90年代初期为了提高操作系统的可移值性、可扩充性和可靠性而出现的。微内核出现的主要原因是出于是于内核的分层操作系统模型存在缺陷,主要是操作系统的每个功能部件都被分成了一系列层。因此功能组件的每部分都受到它所属层接口的限制 5.3 OS Structure 256
  • 257. OS microkernel Problems with the layered OS model can be summarized as follows: The OS kernel has the potential to offer good portability. However it may also contain architecture independent code, which detracts from the goal of portability. The layered architecture of the kernel-based design offers poor extensibility. This is due to the fact that addition of a new functionality requires changes in the interfaces of many OS layers, e.g. new software interrupts have to be devised to activate the code located in the kernel. The reliability of the kernel may be poor because of its not-so-small size. The kernel supports a large number of calls, many of which are infrequently used. Their implementations across different versions of the kernel are likely to be unreliable.分层操作系统的问题可被总结如下:系统内核有潜力提供良好的可移值性,但它同样包含与结构无关的代码,而这恰恰削弱了可移植性。基于内核的分层结构设计的可扩充性很差,这是由于添加新的功能组件意味着需要更改许多层的接口,即需要设计新的软件中断来激活内核中的代码。内核的可靠性不高,因为它并不十分小。内核支持许多的调用,但其中有很多并不常用。所以它们在不同版本的内核间的实现是很不可靠的。5.3 OS Structure 257
  • 258. OS microkernel The OS microkernel is an essential core of the OS code. It provides the minimal functionalities necessary to support architecture independent code. It does not provide a layered interface, instead it supports a few well documented OS calls. This enhances the portability and reliability in an obvious manner. 操作系统微内核是操作系统代码中的重要核心,它提供了支持与结构无关的代码所必需的最小功能组件。它不支持分层接口,而是支持一些有良好文档定义的OS调用。这显然增强了可移植性和可靠性。5.3 OS Structure 258
  • 259. OS microkernel Extensibility is enhanced because many components previously considered to be parts of the OS kernel, e.g. process scheduling, now reside outside it in the OS. These components can be replaced at will to modify or extend the OS behaviour. It is thus possible to use the same microkernel to implement time sharing or dedicated real time systems. This simplifies the development of an OS for a new application domain. 由于以前被认为是内核一部分的组件(如进程调度)现在被放在内核之外,因此可扩充性也增强了。如果想修改或扩展系统性能,可以通过替换这些组件实现,可以使用同一个微内核来实现分时或实时系统,这简化了在新的应用域中对操作系统的开发。5.3 OS Structure 259
  • 260. OS microkernel It is to be noted that microkernel designs vary greatly due to different interpretations of the term 'essential core of OS code'. Variations mainly concern the location of the process scheduler and the device drivers within the OS. For example, the Mach microkernel by IBM leaves the process scheduling policy and the device drivers outside the kernel while certain other microkernels include both these features. 应当注意,微内核的设计会因为对“操作系统代码的重要核心”的不同解释而大相径庭。差异主要集中在系统内的进程调度程序和设备驱动程序的位置,例如IBM的Mach微内核就不包括过程调度策略和设备驱动程序,而其他一些微内核则包括这两项特性。5.3 OS Structure 260
  • 261. OS microkernel Some well-known microkernels include the QNX kernel which is only 8K bytes in size and includes process scheduling, interrupt handling, interprocess communication and core network services.一些知名的微内核包括一个只有8Kb大小,但包含过程调度、中断处理、进程间通信及核心网络服务的QNX内核。5.3 OS Structure 261
  • 262. 被动语态的翻译技巧一、翻译成汉语的主动句 1、英语原文中的主语在译文中仍做主语 在采用此方法时, 我们往往在译文中使用“加以”, “经过”, “用…来”等词来体现原文中的被动含义。 例1. Other questions will be discussed briefly. 其他问题将简单地加以讨论。 例2. In other words mineral substances which are found on earth must be extracted by digging, boring holes, artificial explosions, or similar operations which make them available to us. 换言之, 矿物就是存在于地球上, 但须经过挖掘、钻孔、人工爆破或类似作业才能获得的物质。 262
  • 263. 被动语态的翻译技巧一、翻译成汉语的主动句 2、将英语原文中的主语翻译为宾语, 同时增补泛指性的词语(人们,大家等)做主语 例1. It could be argued that the radio performs this service as well, but on television everything is much more living, much more real. 可能有人会指出, 无线电广播同样也能做到这一点, 但还是电视屏幕上的节目要生动、真实得多。 下列的结构也可以通过这一手段翻译: It is asserted that … 有人主张 …… It is believed that … 有人认为…… It is generally considered that … 大家(一般人)认为 It is well known that … 大家知道(众所周知)…… It will be said … 有人会说…… It was told that … 有人曾经说…… 263
  • 264. 被动语态的翻译技巧一、翻译成汉语的主动句 3、将英语原文中的by, in, for等做状语的介词短语翻译成译文的主语, 而英语原文中的主语一般被翻译成宾语。 例. And it is imagined by many that the operations of the common mind can be by no means compared with these processes, and that they have to be acquired by a sort of special training. 许多人认为, 普通人的思维活动根本无法与科学家的思维过程相比, 而且认为这些思维过程必须经过某种专门的训练才能掌握。 264
  • 265. 被动语态的翻译技巧一、翻译成汉语的主动句 4、翻译成汉语的无主句 例. Many strange new means of transport have been developed in our century, the strangest of them being perhaps the hovercraft. 在我们这个世纪内研制了许多新奇的交通工具, 其中最奇特的也许就是气垫船了。 It is hoped that … 希望…… It is reported that … 据报道…… It is said that … 据说…… It is supposed that … 据推测…… It may be said without fear of exaggeration that … 可以毫不夸张地说… It must be admitted that … 必须承认…… It must be pointed out that … 必须指出…… It will be seen from this that … 由此可见…… 265
  • 266. 被动语态的翻译技巧一、翻译成汉语的主动句 5、翻译成带表语的主动句 例1.The decision to attack was not taken lightly. 进攻的决定不是轻易做出的。 例2. On the whole such an conclusion can be drawn with a certain degree of confidence, but only if the child can be assumed to have had the same attitude towards the test as the other with whom he is being compared, and only if he was not punished by lack of relevant information which they possessed. 总的来说, 得出这种结论是有一定程度把握的, 但必须具备两个条件:能够假定这个孩子对测试的态度和与他比较的另一个孩子的态度相同; 他也没有因为缺乏别的孩子已掌握的有关知识而被扣分。 266
  • 267. 常用英汉互译技巧二、译成汉语的被动语态 英语中的许多被动句可以翻译成汉语的被动句。常用“被”, “给”, “遭”, “挨”, “为……所”, “使”, “由…”, “受到”等表示。 例1. These signals are produced by colliding stars or nuclear reactions in outer space. 这些讯号是由外层空间的星球碰撞或者核反应所造成的。 例2. Over the years, tools and technology themselves as a source of fundamental innovation have largely been ignored by historians and philosophers of science. 工具和技术本身作为根本性创新的源泉多年来在很大程度上被科学史学家和科学思想家们忽视了。 267
  • 268. Computer EnglishChapter 6 Software Engineering
  • 269. 掌握软件的生命周期的基本术语与知识; 了解软件工程的发展趋势; 了解软件设计方法; 了解软件安全的有关知识; 掌握复杂定语(从句)的翻译技巧。Requirements:269
  • 270. New Words & Expressions manufactured products 工业产品 lieu n.场所 software life cycle 软件生命周期 versus prep. 与...相对 nondescriptive adj. 非描述性的 community n.团体, 社会 authorized adj.权威认可的, 经授权的 leverage n.杠杆作用 generic adj. 一般的, 普通的 potential adj.潜在的, 可能的 in terms of adv.根据, 按照, 用...的话 terminology n.术语学 personnel n.人员, 职员 inventory n.详细目录, 财产清册 adhere to v.粘附, 粘着, 坚持, 追随 password n.密码, 口令 specification n.详述, 说明书, 规范 encrypt v.加密,将...译成密码 preprocess vt.预加工,预处理 routine n.程序 modular adj.模块的, 有标准组件的 well-established 充分证实的 decomposition n.分解 breakdown n. 分解,故障 pertaining to 与...有关的 maintenance n.维护, 保持 imperative adj.强制性的,命令式 paradigm n.范例,模式 approach vt.接近,解决;n.近似,途径 conducive adj.有助于...的 evasive adj.逃避的;回避的;推托的 framework n.构架, 框架, 结构270
  • 271. New Words & Expressions take the form of 采取...形式 entity n.实体; 统一体 modular design 标准设计, 模块化设计 object-oriented 面向对象的 stub n.树桩, 桩模块 give way to 让路,让步 trial-and-error n.试错,反复试验 malfunction n.故障,出错 waterfall model 瀑布模型 analogy n.类似, 类推 after all adv.毕竟 stark adv.完全地 trial-and-creative 试验并创造的 nonstructure 非结构性 intuition n.直觉, 直觉的知识 contradiction n.反驳, 矛盾 incremental model 增量式模型 update v.修正, 更新;n.更新 stepwise adj.楼梯式的, 逐步的 prototype n.原型 evolutionary prototyping 演化式原型 in favor of adv.赞同, 有利于 throwaway prototyping 抛弃原型 iron out 消除;解决困难等 documentation n.文件 debugging n.调试 spreadsheet n.电子制表软件, 电子数据表 Abbreviations CASE (computer-aided software engineering) 计算机辅助软件工程 GUI (Graphical User Interfaces) 图形用户界面271
  • 272. 6.1 The Software Life Cycle6.1.1 The Cycle as a WholeFigure 6-1 The software life cycleThe most fundamental concept in software engineering is the software life cycle.软件生命周期是软件工程中最基本的概念。272
  • 273. 6.1.1 The Cycle as a WholeThe software life cycle is shown in Figure 6-1. This figure represents the fact that once software is developed, it enters a cycle of being used and modified that continues for the rest of the software's life. Such a pattern is common for many manufactured products as well. The difference is that, in the case of other products, the modification phase is more accurately called a repair or maintenance phase because other products tend to move from being used to being modified as their parts become worn. 在图6-1中展示了软件的生命周期。这个图说明了一个事实:一旦软件开发完成,它就进入了使用和修改的循环,并且这个循环将在软件生命期的剩余时间中不断进行。这样的模式对机器制造的产品而言也是很普通的。不同之处在于,对于其他产品,软件工程中的修改阶段要被更精确地称作修理或者维护阶段,因为其他产品由于部件的磨损会有从使用到修改的过程。273
  • 274. 6.1.1 The Cycle as a WholeSoftware, on the other hand, does not wear out. Instead, software moves into the modification phase because errors are discovered, because changes in the software's application occur that require corresponding changes in the software, or because changes made during a previous modification are found to induce problems elsewhere in the software. For example, changes in tax laws may require modifications to payroll programs that calculate withholding taxes, and all too often these changes may have adverse effects in other areas of the program that may not be discovered until some time later.当然,软件不存在磨损的问题。但是,软件进入修改阶段或者是因为错误被发现,或者是因为要在软件的应用程序中进行修改从而修改了软件,或者是因为先前的改变又引起了软件其他地方出现了新的问题。例如,税务法案的改变导致对计算扣税的工资程序进行修改,而太频繁的修改则会在软件的其他地方引起反面的作用,而这些是不会被立即发现的。274
  • 275. 6.1.1 The Cycle as a WholeRegardless of why software enters the modification phase, the process requires that a person (often not the original author) study the underlying program and its documentation until the program, or at least the pertinent part of the program, is understood. Otherwise, any modification could introduce more problems than it solves. Acquiring this understanding can be a difficult task even when the software is well-designed and documented. In fact, it is often within this phase that a piece of software is finally discarded under the pretense (too often true) that it is easier to develop a new system from scratch than to modify the existing package successfully 不管因为什么原因软件进入了修改阶段,这个过程需要人们(通常不是原始的作者)研究程序及其文档,直到程序或者至少是相关部分的程序能够被理解。否则,任何的修改将导致比它所解决问题还要更多的问题出现。即使软件有优秀的设计和齐备的文档,理解也是一个很困难的工作。事实上,常常是在这个阶段,一个有用的软件片段最终就被放弃了(常常是这样),而开发一个新的系统比成功地修改现有软件更容易。275
  • 276. 6.1.1 The Cycle as a WholeExperience has shown that a little effort during the development of software can make a tremendous difference when modifications in the software are required. 经验告诉我们,软件开发过程中的一丁点付出,会在软件需要修改的时候带来巨大的不同。In turn, most of the research in software engineering focuses on the development stage of the software life cycle, with the goal being to take advantage of this effort-versus-benefit leverage. 反过来,大多数软件工程的研究都集中于软件生命周期的开发阶段,它们的目标是要利用这个付出与收益的杠杆作用。276
  • 277. 6.1.1 The Cycle as a WholeThe Traditional Development Phase The stages within the development phase of the software life cycle are analysis, design, implementation, and testing (Figure 6-2).软件生命周期的开发阶段包括分析、设计、实现与测试等步骤(如图6-2所示)。277
  • 278. 6.1.1 The Cycle as a WholeThe Traditional Development Phase Analysis The development phase of the software life cycle begins with analysis--a major goal being to identify the needs of the user of the proposed system. If the system is to be a generic product sold in a competitive market, this analysis would involve a broad-based investigation to identify the needs of potential customers. If, however, the system is to be designed for a specific user, then the process would be a more narrow investigation.分析 软件生命周期的开发阶段以分析开始——主要目标是确定用户对所提出系统的需求。如果系统是一个在竞争的市场上销售的通用产品,这个分析将会包括一个广泛的调查来发现潜在用户的需要。但是,如果系统是为特殊用户设计的,那么这个过程就是一个更专业的调查。278
  • 279. 6.1.1 The Cycle as a WholeThe Traditional Development Phase As the needs of the potential user are identified, they are compiled to form a set of requirements that the new system must satisfy. These requirements are stated in terms of the application rather than in the technical terminology of the data processing community. One requirement might be that access to data must be restricted to authorized personnel. Another might be that the data must reflect the current state of the inventory as of the end of the last business day or that the arrangement of the data as displayed on the computer screen must adhere to the format of the paper forms currently in use.当潜在用户的要求被确定之后,要将这些要求汇编成新系统必须满足的需求。这些需求是从应用的角度来表述,而不是用数据处理界的技术术语来表达。一种需求可能是对数据的存取必须限制在有权限的人员,另一种可能是当一个工作日结束时,数据必须反映目前的清单状态,或者可能是在计算机屏幕上的数据必须按照用户目前使用的格式来显示。279
  • 280. 6.1.1 The Cycle as a WholeThe Traditional Development Phase After the system requirements are identified, they are converted into more technical system specifications. For example, the requirement that data be restricted to authorized personnel might become the specification that the system will not respond until an approved eight-digit password has been typed at the keyboard or that data will be displayed in encrypted form unless preprocessed by a routine known only to authorized personnel.系统的需求被确定以后,它们就转化为更具技术性的说明书。例如,关于数据须限制在某些有权限的人的需求,就可能转化为以下规范——直到从键盘输入一个被认可的8位密码,系统才开始响应,或者除非经过只有授权的人才知道的例程预处理,否则数据将以加密的形式显示在屏幕上。280
  • 281. 6.1.1 The Cycle as a WholeThe Traditional Development Phase Design Whereas analysis concentrates on what the proposed system should do, design concentrates on how the system will accomplish those goals. It is here that the structure of the software system is established. 设计 分析关注这个系统应该做什么,而设计关注这个系统应该怎样来实现目标。正是通过设计建立了软件系统的结构。281
  • 282. 6.1.1 The Cycle as a WholeThe Traditional Development Phase It is a well-established principle that the best structure for a large software system is a modular one. Indeed, it is by means of this modular decomposition that the implementation of large systems becomes a possibility. Without such a breakdown, the technical details required in the implementation of a large system would exceed a human's comprehensive powers. 大型软件系统最好的结构是模块化系统,这是一条被充分证实的原则。确实,正是借助模块化的分解方法,大型系统的实现才成为可能。没有这样的分解,在大型系统实现过程中所需要的技术细节可能会超过一个人的理解能力。282
  • 283. 6.1.1 The Cycle as a WholeThe Traditional Development Phase With a modular design, however, only the details pertaining to the module under consideration need be mastered. This same modular design is also conducive to future maintenance because it allows changes to be made on a modular basis. (If a change is to be made to the way each employee's health benefits are calculated, then only modules dealing with health benefits need be considered.)然而,有了这种模块化设计,仅仅需要熟悉与在考虑中的模块相关的细节。同样,模块化设计对未来的维护是有益的,因为它允许对基本的模块进行修改。(如果要对每个雇员的医疗福利计算方法进行修改,那么仅仅需要考虑处理医疗福利模块。)283
  • 284. 6.1.1 The Cycle as a WholeThe Traditional Development Phase There are, however, distinctions regarding the concept of a module. If one approaches the design task in terms of the traditional imperative paradigm, modules consist of procedures and the development of a modular design takes the form of identifying the various tasks that the proposed system must perform. In contrast, if one approaches the design task from the object-oriented perspective, modules are seen as objects and the design process becomes that of identifying the entities (objects) in the proposed system as well as how these entities should behave.但是,有关模块的概念也是有差别的。如果一个人以传统的命令式语言范式的方法来进行设计工作,模块由不同程序组成,而模块化设计则以确定有待实现系统的不同任务的方式进行。相反地,如果一个人从面向对象的角度来完成设计工作,模块就被看成了对象,而设计过程变成了确定有待实现系统中的实体(对象)以及确定这些实体是如何工作的。284
  • 285. 6.1.1 The Cycle as a WholeThe Traditional Development Phase Implementation Implementation involves the actual writing of programs, creation of data files, and development of databases. 实现 实现包括程序的实际编写、数据文件的建立以及数据库的开发等过程。285
  • 286. 6.1.1 The Cycle as a WholeThe Traditional Development Phase Testing Testing is closely associated with implementation, because each module of the system is normally tested as it is implemented. Indeed, each module in a well-designed system can be tested independently of the other modules by using simplified versions of the other modules, called stubs, to simulate the interaction between the target module and the rest of the system. Of course, this testing of components gives way to overall system testing as the various modules are completed and combined.测试 测试与实现紧密联系,因为系统中的每一个模块都要在实现的过程中进行正常测试。确实,通过使用其他模块的简化版本——有时称为桩模块,来模拟目标模块和系统其他部分的交互,从而使设计良好的系统中的每一个模块都可以被独立地测试。当然,在各种模块都开发完成并且整合在一起之后,这个组件的测试将让路给整个系统的测试。286
  • 287. 6.1.1 The Cycle as a WholeThe Traditional Development Phase Unfortunately, the testing and debugging of a system is extremely difficult to perform successfully. Experience has shown that large software systems can contain numerous errors, even after significant testing. Many of these errors may go undetected for the life of the system, but others may cause major malfunctions. The elimination of such errors is one of the goals of software engineering. The fact that they are still prevalent means that a lot of research remains to be done.不幸的是,成功地进行系统的测试和调试是极其困难的。经验表明,大型的软件系统可能包含众多的错误,甚至是经过关键测试之后。许多这样的错误在软件的生命期中一直潜伏着,但是也有一些会导致关键性的错误。减少这样的错误是软件工程的一个目标。这些错误的普遍存在说明了在这方面还有许多的研究工作要做。287
  • 288. 6.1.1 The Cycle as a WholeRecent Trends Early approaches to software engineering insisted on performing analysis, design, implementation, and testing in a strictly sequential manner. The feeling was that too much was at risk during the development of a large software system to allow for trial-and-error techniques. 软件工程的早期方法坚持要严格地遵守分析、设计、实现以及测试的顺序。在大型软件系统的开发过程中,感觉到采用试错法是在冒着很大的风险进行开发的。288
  • 289. 6.1.1 The Cycle as a WholeRecent Trends As a result, software engineers insisted that the entire analysis of the system be completed before beginning the design and, likewise, that the design be completed before beginning implementation. The result was a development process now referred to as the waterfall model, an analogy to the fact that the development process was allowed to flow in only one direction.因此,软件工程师坚持应当在设计之前进行完整的系统分析,同样,设计应该在实现之前完成。这就形成了一个现在称为瀑布模型的开发过程,这是对开发过程只允许以一个方向进行的事实的模拟。289
  • 290. 6.1.1 The Cycle as a WholeRecent Trends You will notice a similarity between the four problem-solving phases identified by Polya and the analysis, design, implementation, and testing phases of software development. After all, to develop a large software system is to solve a problem. 你将注意到由Polya提出的解决问题的4个阶段与软件开发的分析、设计、实现和测试阶段的类似性。毕竟,开发一个大型的软件系统是去解决一个问题。290
  • 291. 6.1.1 The Cycle as a WholeRecent Trends On the other hand, the traditional waterfall approach to software development is in stark contrast to the "free-wheeling ," trial-and-creative problem solving. Whereas the waterfall approach seeks to establish a highly structured environment in which development progresses in a sequential fashion, creative problem solving seeks a nonstructured environment in which one can drop previous plans of attack to pursue sparks of intuition without explaining why. 另一方面,传统软件开发的瀑布模型法与随心所欲的反复试验并创造性地解决问题的方法是完全相反的。瀑布模型法寻求建立一个高度结构化的环境,希望在这个环境中的开发可以顺利地进行,而创造性的问题解决要寻找一个非结构化的环境,希望在这个环境中可以抛弃先前的计划,来追逐思维的火花,而不用解释为什么。291
  • 292. 6.1.1 The Cycle as a WholeRecent Trends In recent years, software engineering techniques have begun to reflect this underlying contradiction as illustrated by the emergence of the incremental model for software development. Following this model, the desired software system is constructed in increments--the first being a simplified version of the final product with limited functionality. 近年来,软件工程技术已经开始反映这种本质的对立了,这可以由软件开发中出现的增量式模型来说明。根据这个模型,所需的软件系统是通过增量模式来构造的——首先开发最终产品的简化版本,它只有有限的功能。292
  • 293. 6.1.1 The Cycle as a WholeRecent Trends Once this version has been tested and perhaps evaluated by the future user, more features are added and tested in an incremental manner until the system is complete. For example, if the system being developed is a student records system for a university register, the first increment may incorporate only the ability to view student records. Once that version is operational, additional features, such as the ability to add and update records, would be added in a stepwise manner.一旦这个版本经过测试、并且也许经过了未来用户的评估,更多的特性就可以添加进去并且进行测试,这样就以一种增量的方式进行,直到完成系统。例如,如果正在开发的系统是为大学登记员设计的学生记录系统,第一次迭代版本仅仅包括浏览学生记录的功能。一旦这个版本可以运行了,其他特性,诸如增加和更新记录的功能,就可以分阶段地添加到系统中了。293
  • 294. 6.1.1 The Cycle as a WholeRecent Trends The incremental model is evidence of the trend in software development toward prototyping in which incomplete versions of the proposed system, called prototypes, are built and evaluated. In the case of the incremental model these prototypes evolve into the complete, final system---a process known as evolutionary prototyping. In other cases, the prototypes may be discarded in favor of a fresh implementation of the final design. This approach is known as throwaway prototyping. 这种增量式模型是软件开发向原型法发展趋势的一个证据——在这种方法中,建立并测试的是不完善系统,它也被称为原型,被评估和测试。在增量式模型中,这些原型进化为一个完整的最终系统——这个过程称为演化式原型。对于其他情况,原型的抛弃会有利于新的最终设计的实现,这种方法就是抛弃原型。294
  • 295. 6.1.1 The Cycle as a WholeRecent Trends An example that normally falls within this throwaway category is rapid prototyping in which a simple example of the proposed system is quickly constructed in the early stages of development. Such a prototype may consist of only a few screen images that give an indication of how the system will interact with the user and what capabilities it will have. 一个抛弃原型的例子就是快速原型法,在这个方法中,系统的简单版本在开发的早期就被很快搭建起来。这样的原型也许仅仅包含少量界面图片来展示系统怎样与用户交互以及它将具有的功能。295
  • 296. 6.1.1 The Cycle as a WholeRecent Trends The goal is not to produce a working version of the product but to obtain a demonstration tool that can be used to clarify communication between the parties involved. For example, rapid prototypes have proved advantageous in ironing out system requirements during the analysis stage or as aids during sales presentations to potential clients.我们的目标不是制作产品的有效版本,而是获得一个示范工具,以便阐明有关方面之间的沟通。例如,在分析阶段解决系统的需求问题,或在销售阶段作为向潜在客户演示的辅助, 快速原型具有很大的优势 296
  • 297. 6.1.1 The Cycle as a WholeRecent Trends Another development in software engineering has been the application of computer technology to the software development process itself, resulting in what is called computer-aided software engineering (CASE). 软件工程领域中另一个发展是计算机技术在软件开发过程本身的应用,这导致了称为计算机辅助软件工程(CASE)的出现。297
  • 298. 6.1.1 The Cycle as a WholeRecent Trends These computerized systems are known as CASE tools and include project planning tools (that assist in cost estimation, project scheduling, and personnel allocation), project management tools (that assist in monitoring the progress of the development project), documentation tools (that artist in writing and organizing documentation), prototyping and simulation tools (that assist in the development of prototypes), interface design tools (that assist in the development of GUIs), and programming tools (that assist in writing and debugging programs). 这些计算机化系统就是知名的CASE工具,且包括项目计划工具(帮助成本估计、项目调度,以及人力资源分配)、项目管理工具(帮助管理开发项目的进程)、文档工具(帮助撰写和组织文档)、界面设计工具(帮助开发GUI)以及程序设计工具(帮助编写和调试程序)。298
  • 299. 6.1.1 The Cycle as a WholeRecent Trends Some of these tools are little more than the word processors, spreadsheet systems, and e-mail communication systems used in other applications. However, others are quite sophisticated packages designed primarily for the software engineering environment. For example, some CASE tools include code generators that, when given specifications for a part of a system, produce high-level language programs that implement that part of the system.这些工具也许仅仅就是在其他的应用程序中的文字处理软件,或者是表格处理软件,或者是电子邮件通讯系统。一些则是相当复杂的软件,它们主要是为了软件工程环境来设计的。例如,一些CASE工具包括了代码生成器,当给出一个系统局部的说明书时,它可用来生成实现这个系统局部的高级语言程序。299
  • 300. 6.2 Design Methodologies The development of methodologies for designing software systems is a major quest within software engineering. In this section we discuss a variety of the techniques that have been developed as well as directions of current research.设计软件系统的方法学是软件工程领域主要探索的方向之一。本节我们将讨论一些已经形成的方法以及当前的研究方向。300
  • 301. 6.2.1 Top-Down Versus Bottom-Up Perhaps the most well-known strategy associated with system design is the top-down methodology. The point of this methodology is that one should not try to solve a complex problem in a single step. Instead, one's first stop should be to break the problem into smaller, more manageable subproblems. Then, one should proceed by breaking these subproblems into still smaller problems. In this manner, a complex problem becomes a collection of simpler problems whose solutions collectively solve the original problem.也许最著名的系统设计策略就是自顶向下的方法学了。这个方法学的要点就是人们不要试图一下子就将一个复杂问题解决,而是应当将问题分解成更小的、可以管理的子问题。然后,将这些子问题分解成更小的问题。以这种方式,一个复杂的问题变成了相对小的问题的集合,而所有小问题的解决就是原问题的解决。 301
  • 302. 6.2.1 Top-Down Versus Bottom-Up The result of top down design tends to be a hierarchical system of refinements that often can be translated directly into a modular structure that is compatible with the imperative programming paradigm. The solutions to the smallest problems in the hierarchy become procedural modules that perform simple tasks and are used as abstract tools by more superior modules to solve the more complex problems in the system. 自顶向下设计的结果是一个逐步求精的层次系统,这个结构通常可以被直接翻译成与命令式语言兼容的模块结构。对层次结构中最小问题的解决变成了执行简单任务的程序模块,这个模块被较高层用作抽象工具来解决系统中更为复杂的问题。302
  • 303. 6.2.1 Top-Down Versus Bottom-Up In contrast to the top-down design methodology is the bottom-up approach, in which one starts the design of a system by identifying individual tasks within the system and then considers how solutions to these tasks can be used as abstract tools in the solution to more complex problems. For many years, this approach was considered inferior to the top down design paradigm. 相对于自顶向下的设计方法学,自底向上的方法确定系统中的每一个具体任务来开始系统的设计。然后,它考虑如何将这些任务的解决用做解决更复杂问题的抽象工具。多年来,这个方法被认为不如自顶向下的设计范式。303
  • 304. 6.2.1 Top-Down Versus Bottom-Up Today, however, the bottom-up methodology has gained support. One reason for this shift is that the top-down methodology seeks a solution in which a dominant module uses submodules, each of which relies on subsubmodules, and so on. 但是,今天,自底向上的方法学又获得了支持。这种转变的一个原因就是自顶向下的方法寻求一个支配模块使用子模快,而每一个支配模块依赖于子模块的解决,等等。304
  • 305. 6.2.1 Top-Down Versus Bottom-Up However, the best design for many systems is not of a hierarchical nature. Indeed, a design consisting of two or more modules interacting as equals, as exemplified by the client-server model as well as general parallel processing applications, may be a better solution than a design consisting of a superior module that relies on subordinates to perform its task.但是,对于许多系统来说,最好的设计不是一个层次的结构。确实,一个设计包括两个或更多模块——它们平等交互,这也是被包含通用并行处理应用程序的客户/服务器模型或者系统所例证了的,比起依赖于从属模块来执行任务的较高级模块构成的设计,它也许是一个更好的解决方案。305
  • 306. 6.2.1 Top-Down Versus Bottom-Up Another reason for increased interest in bottom-up design is that it is more consistent with the goal of building complex software systems from preconstructed, off-the-shelf components--an approach that is a current trend in soft- ware engineering. 对自底向上设计产生更多兴趣的另一个原因,就是它与从预先构建的现成组件中构建复杂软件系统的目标更加一致——这体现了软件工程当前的趋势。306
  • 307. 6.2.2 Design Patterns In an effort to find ways by which software can be constructed from off-the-shelf components, software engineers have turned to the field of architecture for inspiration. Of particular interest is the book A Pattern Language by Christopher Alexander et al., which describes a set of patterns for designing communities. 每种模式都包括了一个问题描述以及建议性的解决方案。这些问题是很普遍的,而这个建议性的解决方案也是一般性的——旨在强调他们阐述的是问题的一般的本质而不是仅仅为一个特殊的例子提出一个解决方案。307
  • 308. 6.2.2 Design Patterns Each pattern consists of the statement of a problem followed by a proposed solution. The problems are intended to be universal, and the proposed solutions are generic in the sense that they address the universal nature of the problem rather than proposing a solution for a particular case.每种模式都包括了一个问题描述以及建议性的解决方案。这些问题是很普遍的,而这个建议性的解决方案也是一般性的——旨在强调他们阐述的是问题的一般的本质而不是仅仅为一个特殊的例子提出一个解决方案。308
  • 309. 6.2.2 Design Patterns For example, one pattern, called Quiet Backs, addresses the need to escape the commotion of a business center for short periods of refreshment. The proposed solution is to design "quiet backs" into business districts. In some cases, the district could be designed around a main street to which all buildings face--thus, providing for quiet side streets behind the buildings. In other cases, "quiet backs" can be obtained by means of parks, rivers, or cathedrals. 例如,一个模式,叫做“安静的后面”,阐述了躲避商业中心的喧嚣而寻求短暂的精力恢复的需求。其建议性的解决方案就是在商业区中设计一个“安静的后面”。在某些情况下,这个商业区要设计在所有建筑都要朝向的主要街道周围——因此可以将安静的辅路铺在建筑的后面。在其他的情况下,“安静的后面”可以采用公园、河流或者是教堂的形式。309
  • 310. 6.2.2 Design Patterns The important point for our discussion is that Alexander's wok attempted to identify universal problems and provide templates for solving them. Today, many software engineers are attempting to apply this same approach to the design of large software systems. In particular, researchers are applying design patterns as a means of providing generic building blocks with which software systems can be constructed.我们所讨论的重点就是Alexander在著作中试图确定的一般性问题并且提供解决它们的模板。今天,许多软件工程师也试图应用同样的方法来设计大型的软件系统。特别地,研究人员正在应用设计模式作为提供软件构建所需通用单元的方法。310
  • 311. 6.2.2 Design Patterns An example of such a pattern is the publisher-subscriber pattern, consisting of a module (the publisher) that must send copies of its “publications” to other modules (the subscribers). As a specific example, consider a collection of data that is being displayed on a computer screen in more than one format--perhaps as a pie graph as well as a bar graph--simultaneously. In this setting, any change in the data should be reflected in both graphs. Thus the software modules in charge of drawing the graphs should be notified when changes in the data occur. In this case, then, the software module maintaining the data plays the role of the publisher that must send update messages to the subscribers, which are the modules charged with drawing the graphs.这种模式的一个例子就是出版商和订户的模式:一个模块(出版商)将其出版物发送给其他模块(订户)。作为一个特殊的例子,考虑在计算机屏幕上同时显示多种格式的数据集,如饼图和条形图。这样,任何对数据的修改都将会被反映在两张图上。因此,当数据发生更改的时候,这个负责画图的软件模块将会被告知。在这种情况下,维护数据的软件模块就会扮演出版商的角色——它必须要给订户发送更新的消息,而这些订户也是模块,它们负责画图。311
  • 312. 6.2.2 Design Patterns Another example of software design pattern is the container-component pattern. It captures the generic concept of a container that contains components that are themselves containers. Such a pattern is exemplified by the directories or folders used by an operating system's file manager. Each of these directories typically contains other directories, which may contain still other directories. In short, the container-component pattern is meant to capture the recursive concept of containers that contain containers.软件设计模式的另一个例子是容器组件模式。它阐述了容器包括一些组件,而组件本身又是容器的一般性概念。这种模式的例子就是操作系统的文件管理器使用的目录或者文件夹。每个这样的目录都包括了其他目录,而这个被包含了的目录可能又包含了其他的目录。简而言之,容器组件模式可以描述容器包含容器的递归概念。312
  • 313. 6.2.2 Design Patterns Once a pattern such as publisher-subscriber or container-component has been identified, software engineers propose the development of skeletal program units, called frameworks, that implement the pertinent features of the pattern's solution while leaving features specific to particular applications as slots to be filled in later. To accompany frameworks, software engineers propose documentation that describes how the framework can be filled in to obtain a complete implementation of the underlying pattern in a particular setting. Such documentation is called a recipe. Collections of frameworks along with their recipes are fondly known as cookbooks.一旦像出版商与订户或者是容器和组件这样的模式被确定,软件工程师就会计划开发一组程序单元作为骨架,这称为框架,它实现模式方法所要解决的主要特征,而将特殊应用程序的特性作为缺口,留待以后填入。为了补充框架,软件工程师提出了如何填充框架的描述文档。这种文挡被称为处方,与处方在一起的框架集被昵称为菜谱。313
  • 314. 6.2.2 Design Patterns Researchers hope that by means of cookbooks, software engineers will finally be able to construct large, complex software systems from off-the-shelf components--the components being frameworks. Early results have indicated that such an approach can significantly reduce the amount of programming required in the development of a new system. 研究人员希望:借助菜谱,软件工程师最终可以从现成的组件——组件就是框架——构建大型的复杂软件系统。早期的结果表明,这种方法可以大大减少开发新系统所需的编程工作量。314
  • 315. 6.2.2 Design Patterns With all the excitement that has been generated in the software engineering community over design patterns, it is interesting to note that Alexander was not pleased with the results of his patterns in architecture. In short, he found that the systems designed from his patterns were lacking in character, and his work since the early 1980s has focused on ways to capture this evasive quality. However, software engineers argue that the goal in software development does not involve such qualities as beauty and character, but instead accuracy and efficiency. Thus, they continue, design patterns will prove to be more successful in the field of software engineering than in architecture.设计模式在软件工程领域中引起了极大的热情,而对于Alexander而言,他对自己应用于建筑学的模式却不是很满意,这是十分有趣的事。他发现根据自己的模式所设计的系统缺乏个性,并且从二十世纪八十年代初开始他主要致力于捕获这个遗漏性质的方法。但是,软件工程师认为软件开发的目标不是去追求诸如美观和个性的特性,而是追求准确和高效。因此,他们将这种方法发扬光大,设计模式在软件工程领域中将比在建筑领域中更加成功。315
  • 316. 复杂定语(从句)的翻译技巧之一 科技英语中,句子的某个中心词常常被若干个后置定语或定语从句所修饰。这是因为英语句法结构重“形合”,任何一个名词或名词词组,为了对它进行完整而明确的阐述,可以借助各种修饰结构(介词短语、不定式短语、分词短语、定语或同位语从句等)像滚雪球那样引出一长串修饰成分。而汉语讲“意合”,各个成分用意义串联,往往不需要连接词,一般句子较短。汉语中,对于一个名词,通常不用“叠床架屋”式的多重修饰语,因为过长的前置定语会使句子拖泥带水、冗长臃肿、晦涩难懂。 由于英汉两种语言的修饰方式有很大差别,所以对于科技英语中含有多重定语或长定语从句的中心词(组)没有现成的对应译法,也就难以用规范的汉语,简练地译出原文复杂的修饰关系。316
  • 317. 复杂定语(从句)的翻译技巧之一 一、先提后述法 适用于结构复杂的并列长定语(从句)。翻译时,首先用“这样(的)”、“这样一些”、“下列(的)”等词语概括所有修饰成分,然后分别叙述各个修饰内容。用这种方法翻译的译文,重点突出、条理清楚。在许多情况下,这是一种翻译并列长定语(从句)行之有效的方法。 例1. A computer is an electronic device that can receive a set of instructions, or program, and then carry out this program by performing calculations on numerical data or by compiling and correlating other forms of information. 译文:计算机是一种电子装置,它能接受一套指令或程序,并通过数据运算,或收集和联系其他形式的信息来执行该程序。 (比较:计算机是一种能接受一套指令或程序,并通过数据运算,或收集和联系其他形式的信息来执行该程序的电子装置) 例2. A sound card is a printed circuit board that can translate digital information into sound and back, that plug into a slot on the motherboard (the main circuit board of a computer) and is usually connected to a pair of speakers. 译文:声卡是一块印刷电路板,它能把数字信息译为声音,也能把声音变为数字信息,它插在母板(计算机主电路板)上的槽内,而且通常连接一对喇叭。 (比较:声卡是一块能把数字信息译为声音,也能把声音变为数字信息,插在母板(计算机主电路板)上的槽内,而且通常连接一对喇叭的印刷电路板。)317
  • 318. 复杂定语(从句)的翻译技巧之一 二、先述后提法 此译法是“先提后述法”的倒置。也就是先叙述中心词(组)的修饰内容,最后用“这样的”、“这一切”、“这种”、“这些”等词语予以呼应。 例1. The fact that the Government may have formulated, furnished, or in any way supplied the said drawings, specifications, or other data is not to be regarded by implication … 译文:政府可能已经系统地阐述、提供或以某种方式供应了上述图纸、规范或其他资料,但这样的事实并非暗示…… (比较:政府可能已经系统地阐述、提供或以某种方式供应了上述图纸、规范或其他资料的这一事实,并非暗示是……) 例2. The way in which a number of processor units are employed in a single computer system to increase the performance of the system in its application environment above the performance of single processor is an organizational technique. 译文:将许多处理器组成单一的计算机系统,从而提高该系统在其运行环境中的性能,使其超过单个处理器的性能,这种方法称为组织技术。 (比较:将许多处理器组成单一的计算机系统,从而提高该系统在其运行环境中的性能,使其超过单个处理器的性能的方法称为组织技术。) 318
  • 319. Computer English Chapter 7 Programming Languages
  • 320. Key points: useful terms and definitions of programming languages Difficult points: describing the differences between compilers and interpreters320
  • 321. Requirements:1. The origins of the programming languages 2. The concepts of computer compilers3. Main properties of object-orientation4. 了解UML,掌握复杂定语从句的翻译技巧 321
  • 322. New Words & Expressions: evolution n. 发展,演变 primitive 原始的, appropriating 适当的 interpreter 解释程序 compiler 编译器 intermediary 中间的 invoke 调用 premium 额外费用,奖金 cryptic 秘密(含义模糊)的 esoteric 深奥的 prompt n.提示符7.1 Computer Languages Abbreviations: 322
  • 323. Computer languages have undergone dramatic evolution since the first electronic computers were built to assist in telemetry calculations during World War Ⅱ. Early on, programmers worked with the most primitive computer instructions: machine language. These instructions were represented by long strings of ones and zeros. Soon, assemblers were invented to map machine instructions to human-readable and manageable mnemonics, such as ADD and MOV. 自从第一代电子计算机在第二次世界大战中用于自动计算以来,计算机语言已发生了巨大的变化。早期编程员使用最原始的计算机指令——机器语言来工作。这些指令由一长串的0、1组成。不久,发明了汇编程序,它能将机器指令转换成易读、易管理的助记符,如ADD、MOV等。7.1 Computer Languages 323
  • 324. 7.1 Computer LanguagesIn time, higher-level languages evolved [1], such as BASIC and COBOL. These languages let people work with something appropriating words and sentences. Such as Let I=100. These instructions were translated back into machine language by interpreters and compilers. An interpreter translates a program as it reads it, turning the program instructions, or code, directly into actions. A compiler translates the code into an intermediary form. This step is called compiling, and produces an object file. The compiler then invokes a linker, which turns the object file into an executable program. 随后,又推出了高级语言,如BASIC和COBOL.。这些语言使用的是近似于人常用的词句,如Let I=100。这些指令由解释器或编译器翻译成机器语言。解释器边读边翻译,将程序指令或代码直接实现。编译器把代码翻译成中间代码。这一部叫做编译,然后生成目标文件。编译程序调用链接程序,链接程序将目标代码转变成可执行程序。324
  • 325. Ironically, in order to become easier to use for this new audience, programs have become far more sophisticated. Gone are the days when users typed in cryptic commands at esoteric prompts, only to see a stream of raw data. Today’s programs use sophisticated “user-friendly interfaces,” involving multiple windows, menus, dialog boxes with which we’ve all become familiar. The programs written to support this new approach are far more complex than those written just ten years ago. 为使程序更易于被新用户使用,程序本身反而变得越来越复杂。用户需在抽象的提示符下键入难于理解的命令,只能看到一串原始数据的时代已经一去不复返了。如今,程序使用了复杂的“友好用户界面”,包含我们已很熟悉的多窗口、菜单、对话框。支持这些新方法的程序比十年前复杂得多。 7.1 Computer Languages325
  • 326. New Words & Expressions: object-oriented 面向对象的 ongoing adj. 正在进行中的 crisis n. 危机 exploit v. 开发,使用 raw adj. 天然的,原始的 medium n. 媒介,方法 match 相称,匹配 discrete adj. 单个的,离散的 transistor n. 晶体管 resistor n. 电阻 capacitor n. 电容 integration 集成电路 abstraction n. 抽象化 class n. 类 inheritance n. 继承 encapsulation n. 封装 polymorphism n. 多型 entity n. 实例,实体 7.2 Object-Oriented Programming Abbreviations : OOP ( Object-Oriented Programming) 面向对象的编程技术 IC (integrated circuits) 集成电路 LSI(large-scale integration) 大规模集成电路 VLSI(very large-scale integration) 超大规模集成电路326
  • 327. 7.2 Object-Oriented Programming Ever since computers became available in the 1950s, it has been software that exploited its power to solve application problems [2]. Machine code, capable of driving the raw hardware, was the first language available to programmers. Sequences of code statements were the earliest form of software. It was soon recognized that the communication medium between programmer and computer is a critical factor in the programming productivity and quality of the overall software product. 自从50年代计算机开始进入实用阶段以来,软件就在解决应用问题的能力方面崭露头角。控制基本硬件的机器代码是程序员使用的第一种语言。顺序代码语句是软件的最早形式。人们很快就认识到,编程效率和整个软件产品质量的关键因素是程序员和计算机之间的通信手段。327
  • 328. 7.2 Object-Oriented ProgrammingWhile computers, the hardware, underwent revolution after revolution, using faster and ever more powerful components, the software technology has significantly lagged behind in matching these advances. Hardware technology has been revolutionized several times: from tubes to discrete transistors, resistors and capacitors to board-level integration to integrated circuits. Even integrated circuits have undergone several significant evolutionary steps: from large-scale integration (LSI) technology to very large scale integration (VLSI), and eventually wafer scale integration. Hardware engineering was able to keep up with this pace by developing new techniques to manage the exploding complexity of a modern computer system. 当计算机硬件由于使用速度更快、功能更强的器件而不断更新换代的时候,软件技术则大大滞后,与硬件的发展不相匹配。硬件技术已经历了几次革命:从电子管到单个晶体管、电阻和电容器元件,到板级集成电路,到整个集成电路。即使是集成电路也经历了几次重大的演变:从大规模集成电路(LSI)技术到超大规模集成电路(VLSI),并且又发展了晶片上大规模集成技术。硬件工程能够保持这种发展势头,是因为新技术的发展可以对付现代计算机系统与日俱增的复杂性。328
  • 329. 7.2 Object-Oriented ProgrammingEver since computers were used to solve application problems, it was the task of software to bridge the gap between concepts in an application and computer concepts. Fig. 7-1 illustrates this semantic gap. On one side of the gap are the concepts of an application: for example, customer files to organize, accounts to maintain, or rockets to launch. On the other side are the concepts understood by a computer system: electric impulses, micro code, machine code instructions, and programming language constructs. The typical programming task is to translate the application concepts into computer concepts. If the translation succeeds and the computer solves the application problem, a successful software product has been developed. 自从计算机用于解决应用问题以来,软件的任务就是在应用概念和计算机概念之间架起一座桥梁。图7-1表示这种语义间隔,其一端是应用概念,如客户文件的组织,账户的维护或火箭的发射;另一端是计算机系统所理解的概念,电脉冲,微代码,机器代码指令和程序设计语言结构。典型的程序设计任务是将应用概念翻译成计算机概念。如果翻译成功了,并且计算机也解决了这个应用问题,一个成功的软件产品就开发出来了。329
  • 330. 7.2 Object-Oriented ProgrammingAdvances in software technology are driven by the desire to make the transition from application concepts to computer concepts easier. Advances in software technology have narrowed the gap from both sides. On one side they provided software design principles and techniques that allow the programmer to express an application problem closer to computer system terms. Software design principles, such as abstraction, information hiding, modularization and stepwise refinement, allow the programmer to conceptualize application concepts and to ease their transformation into computer system concepts. 希望较容易地把应用概念转变为计算机概念这一愿望推动着软件技术的进步,这种进步从两端使间隙变窄了。在一端,软件技术的进步提供一些软件设计原理和技术,使得程序员用更接近于计算机系统的术语表达应用问题。软件设计原理,诸如抽象化、信息隐蔽、模块化和分段优化,允许程序员对应用概念概念化,从而更容易地将之转变成计算机系统概念。 On the other side, software technology has advanced the expressive power of the tools used to manipulate a computer system: the programming languages. 在另一端,软件技术的发展使得操纵计算机系统的工具——程序设计语言具有更强的表达能力。。330
  • 331. 7.2 Object-Oriented ProgrammingIn the late 1960s it was recognized that a combination of both forces-software design technology and advances in programming languages-may be possible. The resulting language construct was a class. A class implements the concepts of abstraction, modularization, and data hiding, It does so by grouping a user-defined type with all procedures and functions that can be applied to it. Classes allow inheritance.The concept of inheritance relates to the design concept of stepwise refinement and also allows the reuse of existing code and data structures in a class. 60年代末,认识到将两种力量(即软件设计技术和程序设计语言的进展)结合起来是可能的,这样形成的语言结构就是“类”。类通过按所有过程和函数对用户定义的类型进行分组而实现抽象化、模块化和数据隐蔽的概念。类允许继承,继承的概念与分段优化的设计概念相关并允许重新使用在同一类中的现有代码和数据结构。 331
  • 332. 7.2 Object-Oriented ProgrammingThe engineering of a class concept represents a step to software technology similar to the development of an integrated circuit (IC) to hardware. As new hardware systems can be built by using (or modifying) off-the-shelf ICs, it is now possible to build software systems by reusing (or extending) off-the-shelf classes. "Class" is the central concept in object-oriented programming. Object-oriented programming promises to significantly narrow the semantic gap. 类的概念工程象征着朝向软件技术迈开的一步,类似于集成电路的开发对于硬件的贡献。如同可以通过使用或修改流行的集成电路来做新的硬件系统一样,可以重新使用或扩展现有的类去构成软件系统。“类”是面向对象程序设计的核心概念。面向对象的程序设计有望缩小以上所提到的语义间隙。 332
  • 333. 7.2 Object-Oriented ProgrammingSome of the benefits and flexibility of object-oriented programming stem from this separation of function invocation and implementation. The invocation of a functionality is termed "the sending of a message to an object." The execution of its implementation is termed "the receiver of the message executes the corresponding method." The separation of message and method greatly adds to the flexibility possible in an object-oriented program. In our example messages are sent to the plane objects. Each plane object receives a message and executes its desired behavior. In effect, our program "computes" by sending messages to all participating objects. In general, we can observe an object-oriented program as a collection of objects that communicate by sending messages. 面向对象的程序设计的一些优点和灵活性源于将功能的引发和实现相互分离这一技术。功能的引发可表达为“把信息送给对象”。实现的过程被称为“信息接收者执行相应的方法”。信息和方法的分离大大地增加了面向对象程序灵活性。在我们的例子中,信息是送给飞机对象的,每一飞机对象接收一个信息并执行其所要求的行为。实际上,我们的程序通过向所有在场的对象发送信息而进行“计算”。一般来讲,我们可以把面向对象的程序看作是通过发送信息进行通信的各个对象的集合。 333
  • 334. 三、解环法 这种方法适用于翻译“连环式”后置定语或定语从句,也就是当原文中的一个中心词(组)被若干个定语(从句)一环扣一环地修饰时,可先将中心词(组)译出,或把中心词(组)与靠近它的一个或两个后置定语(从句)译成汉语偏正词组,然后顺着“修饰环”依次翻译其余成分。 采用这种方法译出的句子层次分明,脉络清楚。由于科技英语中“连环式”修饰语出现较多,所以“解环法”具有较大的实用价值。例如: A flight simulator is a perfect example of programs that create a virtual reality, or computer-generated “reality” in which the user dose not merely watch but is able to actually participate. 译文:飞行模拟器是创造虚拟现实的程序的一个完美例子,或者也可以叫它计算机生成的“现实”,在这个“现实”中,用户不仅能看,而且能实际参与。 (比较:飞行模拟器是创造虚拟现实,或者也可以叫它计算机生成的,用户不仅能看,而且能实际参与的“现实”的程序的一个完美例子。)复杂定语(从句)的翻译技巧之二 334
  • 335. 复杂定语(从句)的翻译技巧之二三、解环法 再如:Object-oriented databases store and manipulate more complex data structures, called “object”, which are organized into hierarchical classes that may inherit properties from classes higher in the chain; this database structure is the most flexible and adaptable. 译文:面向对象的数据库可以存储并处理更加复杂的数据结构,这种数据结构称为“对象”,“对象”可以按层次组成“类”,低层的“类”可以继承上层“类”的属性;这是一种最灵活,最具适应性的数据结构。 (比较:面向对象的数据库可以存储并处理更加复杂的、称为“对象”的,可以按层次组成“类”的,低层的“类”可以继承上层“类”属性的数据结构;这是一种最灵活,最具适应性的数据结构。) 在英语科技文献中,对于某些连环式修饰语,有时还需同时借助“先提后叙法”,才能使语句顺畅。例如:335
  • 336. 复杂定语(从句)的翻译技巧之二It (chapter 2) provides numerous solutions for protecting problems associated with any type of instruments using microprocessors that must be protected when voltage supply fluctuates. 此句属连环式修饰。由于各个修饰环扣得很紧原文中,protecting problems 并非仅仅与 associated with … instruments有关, (定语从句本身带有一个较长的状语)。因此,译成汉语时,为了使修饰成分紧扣修饰对象,既不宜直接译成偏正词组这会造成“大肚子”句,见译文(1);也不宜用“解环法”法逐个翻译修饰环这会导致修饰语与中心词关系松弛,见译文(2)。此时可采用“解环法+先提后叙法”,也就是先译出一两个修饰环,再用“这样的”、“这样一些”等词语“扣”住中心词,最后叙述具体修饰内容。这样,不但句子修饰关系明确,而且行文较为流畅,见译文(3)。 (1) 第二章提供与使用当供电电压波动时必须加以保护的微处理器的任何类型仪器有关的保护问题的许多解决办法。 (2) 第二章提供与任何类型仪器有关的保护问题的许多保护办法,这类仪器使用微处理器,这些微处理器当供电电压波动时必须予以保护。 (3) 第二章提供解决某些保护问题的许多办法,这些保护问题与任何使用这样一些微处理器的仪器有关:当供电电压波动时时,必须予以保护。336
  • 337. 复杂定语(从句)的翻译技巧之二三、解环法+先提后叙法 例句. This is a software of flight simulator running on personal computers, intended primarily for computer-aided instruction which requires providing practice navigation and instruments reading while users immerse in the virtual environment. 这个句子中的修饰关系也是“连环式”。由于某些修饰环(如 of …和running …, intended … 和which … )扣得紧,加上which引导的定语从句本身含有一个 while 引导的状语从句,所以此句也适于采用“解环法+先提后叙法”。全句可译为: 这是一个运行于个人计算机的飞行模拟器软件,这种软件主要用于如下计算机辅助教学:当用户投入虚拟环境时,它必须提供导航和仪表读数。 由此可见,翻译“连环式”修饰成分要因句制宜,灵活处理,不能只着眼于表面的修饰关系,还要考虑“修饰环”之间的紧密程度。通常,如果“修饰环”彼此关系较松,适于采用“解环法”;要是“扣”得很紧,则可采用“解环法+先提后叙法”。337
  • 338. 复杂定语(从句)的翻译技巧之二四、句子结构调整法 有时,原文句中一个中心词带有若干修饰成分,但它们既不是纯“并列”头系,也不是规则的“连环”关系,而是“并列”中有“连环”(例1),或“连环”中含不规则“修饰环”(例2);或者句中各有一个分别被“连环式”定语和“并列式”定语所修饰的中心词(例3);或者中心词的定语从句本身又含有其他修饰成分(例4)。由于这类句子所含的修饰关系比较复杂,很难纳入上述几种译法予以表达,此时就应该根据上下文的逻辑关系,调整句子结构。常用的方法是:“化整为零”,将带有多重定语(从句)的长句拆译成若干汉语短句,然后按汉语表达习惯组织译文句子。例如: 例1. An operating system is a master control program, permanently stored in memory, that interprets user commands requesting various kind of service, such as display, print, or copy a data file, list all files in a directory, or execute a particular program. 译文:操作系统是主控程序,永久地驻留在内存中,它理解用户的各种指令:如显示、打印文件,将目录中所有文件列表,或者执行一个特殊的程序。 (比较:操作系统是永久地驻留在内存中的;理解用户的各种指令:如显示、打印文件,将目录中所有文件列表,或者执行一个特殊的程序主控程序。) 338
  • 339. 复杂定语(从句)的翻译技巧之二例2. The users of such a system control the process by means of a program, which is a set of instruction that specify the operation, operands, and the sequence by which processing has to occur. 译文:该系统用户通过程序控制处理过程,所谓程序是一套指定操作、操作数和处理序列的指令集。(比较:该系统用户通过一套指定操作、操作数和处理序列的指令集即程序控制处理过程。) 例3. Indeed, today's products -- most of all, the latest in speech recognition – are a roll-out of technologies that have been percolating for years and that are based on an understanding of speech that has taken several decades to accumulate. 译文:的确,今日的产品,尤其是语音识别方面最新的产品,是过去多年技术渗透的延伸,也是基于几十年来对语音理解的结果。 (比较:的确,今日的产品,尤其是语音识别方面最新的产品,是过去多年的渗透和基于几十年来对语音理解的积累的技术延伸。) 例4. The computer family, in computer science, is a term commonly used to indicate a group of computers that are built around the same microprocessor or around a series of related microprocessors, and that share significant design feature. 译文:在计算机科学中,计算机系列是常用的一个术语,通常指一组用相同的或者一系列相关的微处理器制造的计算机。 339
  • 340. Computer EnglishChapter 8 The Internet: Technology Background
  • 341. 了解Internet的起源 掌握Internet的关键技术概念 描述 Internet协议与应用程序的作用 解释当前Internet的结构 理解当前Internet的局限 描述Internet II的潜在作用 掌握英语长句的翻译技巧Requirements:341
  • 342. 8.1 The Internet: Technology Background New Words & Expressions hyperlink n.[计]超链接 pundit n. 空谈家, 权威性的评论者 glibly adv.流利地, 流畅地 conceptualize v.使有概念 legitimization n.合法化, 认为正当 institutional adj.制度上的,机构上的 fledging n.刚会飞的幼鸟,无经验的人 follow-on 继续 slice vt.把...切成薄片; 把...分成部分 break down 破坏;拆散细分;分类 disabled n.禁止使用的 quad n. 四元组 mainframe n.[计]主机, 大型机 vulnerable adj.易受攻击的, gigabyte n.十亿字节(giga-为字首,“十亿”) supercomputer n.[计] 超型计算机 reminiscent adj. 怀旧的;回忆的 Domain Name 域名 host computer (host) 主机 instant messaging 即时信息服务 packet-switching 分组交换技术 client/server 客户机/服务器 circuit switching 线路转接 bit n.[计]位, 比特 Router [计] 路由器 routing algorithm 路径算法 Ethernet n.以太网 token ring networks 令牌环形网 Telnet 远程登录 Finger 查找因特网用户的程序 Ping 测试IP地址的程序 Tracert 检查路由器程序 UNIX 美国AT&T公司的操作系统, UNIX操作系统 let alone 更不用说…342
  • 343. Abbreviations TCP (Transfer Control Protocol) 传输控制协议 IP(Internet Protocol) 网际协议 FTP (File Transfer Protocol) 文件传输协议 POP (Post Office Protocol)邮局协议 HTTP(Hypertext Transfer Protocol)超文本传输协议 IP address IP地址 URL (Uniform Resource Locator) 统一资源定位 DNS (domain name system) 域名系统 SSL (Security Socket Layer) 加密套接字协议层 RAM (random access memory) 随机存储器 ARPANET (Advanced Research Projects Agency Network) 美国国防部高级研究计划局建立的计算机网 ICANN (Internet Corporation for Assigned Names and Numbers) 因特网域名与地址管理组织 SMTP (Simple Message Transfer Protocol)简单邮件传输协议, 用于电子邮件的传输 IMAP (Internet Message Access Protocol) Internet消息访问协议343
  • 344. What is the Internet? Where did it come from, and how did it support the growth of the World Wide Web? What are the Internet’s most important operating principles? The Internet is an interconnected network of thousands of networks and millions of computers (sometimes called host computers or just hosts) linking businesses, educational institutions, government agencies, and individuals together. The Internet provides around 400 million people around the world (and over 170 million people in the United States) with services such as e-mail, newsgroups, shopping, research, instant messaging, music, videos, and news. No one organization controls the Internet or how it functions, nor is it owned by anybody, yet it has provided the infrastructure for a transformation in commerce, scientific research, and culture. 因特网是什么? 它来自何处,和它如何支持万维网的增长? 因特网最重要的运行原则是什么?因特网是成千上万的网络和数以百万计的计算机(有时被称为主机计算机或主机)将企业、教育机构、政府机关和个人联结起来的一个互联网络。因特网为全球大约4亿人(其中美国1.7亿多人)提供诸如电子邮件、新闻讨论组、购物、研究、即时信息、音乐、视频和新闻等服务。没有任何组织控制因特网或它的运作,它也不被任何人所拥有,尽管它为商业交易、科学研究和文化提供基础设施。344
  • 345. The word Internet is derived from the word internetwork or the connecting together of two or more computer networks. The World Wide Web, or Web for short, is one of the Internet’s most popular services, providing access to over one billion Web pages, which are documents created in a programming language called HTML and which can contain text, graphics, audio, video, and other objects, as well as “hyperlinks” that permit a user to jump easily from one page to another. 因特网(Internet)一词起源于互联网络(internetwork)或两个或更多的计算机网络联接在一起。全球信息网,或简称万维网,是因特网上最流行的服务之一,提供对10亿多网页的访问,这些网页是由一种叫做HTML(超文本链接标示语言)编程语言生成的文件,它可以包含本文、图形、声频、视频和其他对象、以及允许用户容易地跳跃到其他网页的“超链接”。345
  • 346. 8.1.1 THE EVOLUTION OF THE INTERNET 1961–2000 Internet I—today’s Internet—has evolved over the last forty years. In this sense, the Internet is not “new”; it did not happen yesterday. Although journalists and pundits talk glibly about “Internet” time—suggesting a fast-paced, nearly instant, worldwide global change mechanism, in fact, it has taken forty years of hard work to arrive at today’s Internet.因特网I——今天的因特网——已经发展了四十多年。在这个意义上,因特网不是“新的”,它不是昨天才发生的事。虽然新闻记者和博学家口若悬河地谈论“因特网”时代——指一种快步调的、几乎即时的、全球性的变化机制,事实上,因特网达到今天的水平花费了四十年的艰苦努力。346
  • 347. The history of the Internet can be segmented into three phases. In the first phase, the Innovation Phase, from 1961 to 1974, the fundamental building blocks of the Internet were conceptualized and then realized in actual hardware and software. The basic building blocks are: packet-switching hardware, client/server computing, and a communications protocol called TCP/IP (all described more fully below). The original purpose of the Internet, when it was conceived in the late 1960s, was to link together large mainframe computers on college campuses. This kind of one-to-one communication between campuses was previously only possible through the telephone system or postal mail. 因特网的历史可以划分为三个阶段。在第一阶段即发明阶段,从1961年到1974年,因特网的基本构建模块被概念化并随之用真正的硬件和软件实现。其基本的构建模块是:分组交换硬件、客户机/服务器计算技术和一个被称为传输控制协议的通信协议(它们都将在后文进行全面描述)。当在20世纪60年代末期构思的时候,因特网最初的目的是将大学校园内的大型计算机联结起来。在校园之间这种一对一的通信先前只有经过电话系统或邮政邮件才可能进行。 8.1.1 THE EVOLUTION OF THE INTERNET 1961–2000 347
  • 348. In the second phase, the Institutional Phase, from 1975 to 1995, large institutions such as the Department of Defense and the National Science Foundation provided funding and legitimization for the fledging invention called the Internet. Once the concept of the Internet had been proven in several government-supported demonstration projects, the Department of Defense contributed a million dollars to develop the concepts and demonstration projects into a robust military communications system that could withstand nuclear war. This effort created what was then called ARPANET (Advanced Research Projects Agency Network). In 1986, the National Science Foundation assumed responsibility for the development of a civilian Internet (then called NSFNet) and began a ten-year-long $200 million expansion program.在第二阶段即机构化阶段,从1975年到1995年,像国防部和国家科学基金委等一些大机构为这项被称为因特网的刚刚起步的发明提供资金并使其合法化。当因特网的概念在一些政府支持的示范性项目中被证实后,国防部提供了一百万美元资金将这个概念和示范性项目发展成为一个可以承受核战的军事通信系统。这个努力产生了以后被称作ARPANET的东西(高级研究计划局建立的计算机网)。在1986年,国家科学基金委承担了建立民用因特网的任务(那时叫做NSFNet),并且开始了为期十年、耗资2亿美元的扩展计划。8.1.1 THE EVOLUTION OF THE INTERNET 1961–2000 348
  • 349. In the third phase, the Commercialization Phase, from 1995–2001, government agencies encouraged private corporations to take over and expand both the Internet backbone and local service to ordinary citizens—families and individuals across America and the world who were not students on campuses. By 2000, the Internet’s use had expanded well beyond military installations and research universities. 在第三阶段即商业化阶段,从1995年至2001年,政府机构鼓励私营公司接管并扩展因特网主干和接管为普通市民提供的地方性服务,普通市民包括在全美国和全世界的家庭以及非在校学生等个体。到2000年,因特网的应用已大大超出了军事设备和大学研究的范围。8.1.1 THE EVOLUTION OF THE INTERNET 1961–2000 349
  • 350. 8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS In 1995, the Federal Networking Council (FNC) took the step of passing a resolution formally defining the term Internet. “Internet” refers to the global information system that— is logically linked together by a globally unique address space based on the Internet Protocol (IP) or its subsequent extensions/follow-ons;在 1995 年,联邦的网络委员会(FNC)通过了一个关于因特网术语正式定义的决议。 “因特网”是这样的全球信息系统—— 通过以因特网协议或其扩展或继续为基础的、独特的地址空间被逻辑性地联结起来;350
  • 351. 8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS II. is able to support communications using the Transmission Control Protocol/Internet Protocol (TCP/IP) suite or its subsequent extensions/follow-ons, and/or other IP-compatible protocols; and III. provides, uses or makes accessible, either publicly or privately, high level services layered on the communications and related infrastructure described herein. II.能够支持使用TCP/IP(传输控制协议/因特网协议)组或其扩展/继续、和/或其他与IP协议(因特网协议)兼容的协议进行的通信;并且 III.提供、使用或使可访问此处描述的通信及其相关基础设施(不论公用的还是专用的)上分层次的高水平服务。 351
  • 352. Based on the definition, the Internet means a network that uses the IP addressing scheme, supports the Transmission Control Protocol (TCP), and makes services available to users much like a telephone system makes voice and data services available to the public2.基于这个定义,因特网表示这样一个网络——使用IP地址分配方案、支持传输控制协议,并使用户可以使用多种服务——与电话系统使公众能够使用声音和数据服务非常类似。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 352
  • 353. Behind this formal definition are three extremely important concepts that are the basis for understanding the Internet: packet switching, the TCP/IP communications protocol, and client/server computing3. Although the Internet has evolved and changed dramatically in the last 30 years, these three concepts are at the core of how the Internet functions today and are the foundation for Internet II.在这个正式的定义背后,隐含着三个极其重要的概念:分组交换、TCP/IP(传输控制协议/网际协议)通信协议和客户机/服务器计算技术,它们乃是理解因特网的基础。尽管因特网在过去30年发生了引人注目的进化和变化,但这三个概念仍是今天因特网运转的核心,也是因特网II的基础。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 353
  • 354. Packet Switching. Packet switching is a method of slicing digital messages into parcels called “packets,” sending the packets along different communication paths as they become available, and then reassembling the packets once they arrive at their destination. Prior to the development of packet switching, early computer networks used leased, dedicated telephone circuits to communicate with terminals and other computers. In circuit-switched networks such as the telephone system, a complete point-to-point circuit is put together, and then communication can proceed. 分组交换。分组交换是传输数据的一种方法,它先将数据信息分割成许多称为“分组”的数据信息包;当路径可用时,经过不同的通信路径发送;当到达目的地后,再将它们组装起来。在分组交换发展之前,早期计算机网络使用租用的专用电话线路和终端与其他计算机进行通信。在线路交换网络如电话系统中,一个完全点对点的线路被连结在一起,然后才能进行通信。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 354
  • 355. However, these “dedicated” circuit-switching techniques were expensive and wasted available communications capacity—the circuit would be maintained regardless of whether any data was being sent. For nearly 70% of the time, a dedicated voice circuit is not being fully used because of pauses between words and delays in assembling the circuit segments, both of which increased the length of time required to find and connect circuits. A better technology was needed.然而,这些“专用的”线路交换技术既价格昂贵又浪费有效的通信能力——不论是否有数据输送都需要维持线路。由于字间的停顿和组装时的延迟,一条专用的声音线路在几乎70%的时间内没有得到充分利用,而这两种因素都增加寻找和连接线路所需的时间长度。因此需要一种比较好的技术。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 355
  • 356. The first book on packet switching was written by Leonard Kleinrock in 1964, and the technique was further developed by others in the defense research labs of both the United States and England. With packet switching, the communications capacity of a network can be increased by a factor of 100 or more. The communications capacity of a digital network is measured in terms of bits per second. Imagine if the gas mileage of your car went from 15 miles per gallon to 1,500 miles per gallon—all without changing too much of the car! 第一本关于分组交换的著作是由Leonard Kleinrock于1964年所著,美国和英国防卫研究实验室的其他研究人员使这项技术得到进一步发展。由于使用分组交换技术,网络的通信能力提高了100倍甚至更多。数字网络的通信能力用每秒位来衡量。想象一下汽车行驶的里程,从每加仑汽油行驶15里提高到每加仑汽油行驶1500 里——而汽车没有太大的改变!8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 356
  • 357. In packet-switched networks, messages are first broken down into packets. Appended to each packet are digital codes that indicate a source address (the origination point) and a destination address, as well as sequencing information and error control information for the packet. Rather than being sent directly to the destination address, in a packet network, the packets travel from computer to computer until they reach their destination. These computers are called routers. Routers are special purpose computers that interconnect the thousands of different computer networks that make up the Internet and route packets along to their ultimate destination as they travel4. To ensure that packets take the best available path toward their destination, the routers use computer programs called routing algorithms.在分组交换的网络中,信息首先被分解为许多信息包。每个信息包附加数字代码用于指示其源地址(开始点)和目的地地址、以及顺序信息和错误控制信息。在分组网络中,信息包不是直接被送到目的地地址,而是在计算机与计算机之间旅行直到它们到达目的地。这些计算机叫做路由器。路由器是一种特殊用途的计算机,它将组成因特网的成千上万个不同计算机网络互相联接起来,并在信息包旅行时将它们的向终极目的地发送。路由器使用一种叫做路由算法的计算机程序,以确保信息包取通向它们目的地的最佳可用路径。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 357
  • 358. Packet switching does not require a dedicated circuit but can make use of any spare capacity that is available on any of several hundred circuits. Packet switching makes nearly full use of almost all available communication lines and capacity. Moreover, if some lines are disabled or too busy, the packets can be sent on any available line that eventually leads to the destination point. 分组交换不需要一个专用线路,但是可以利用几百条线路中任何可用的空闲能力。分组交换几乎充分利用了所有可用的通信线路和能力。而且,如果一些线路不通或太忙的话,信息包能在任何可用的、最终通向目的地的线路上传送。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 358
  • 359. TCP/IP. While packet switching was an enormous advance in communications capacity, there was no universally agreed upon method for breaking up digital messages into packets, routing them to the proper address, and then reassembling them into a coherent message. This was like having a system for producing stamps, but no postal system (a series of post offices and a set of addresses).TCP/IP。尽管分组交换是通信能力的一个巨大进步,但对于将数字信息分解为信息包、将它们传输到适当的地址, 然后重新组装为原来的信息,还没有一种公认的方法。这就像有了一个生产邮票的系统,而没有邮政系统(一系列的邮局和一套住址)一样。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 359
  • 360. TCP/IP answered the problem of what to do with packets on the Internet and how to handle them. TCP refers to the Transmission Control Protocol (TCP). IP refers to the Internet Protocol (IP). A protocol is a set of rules for formatting, ordering, compressing, and error-checking messages. It may also specify the speed of transmission and means by which devices on the network will indicate they have stopped sending and/or receiving messages. Protocols can be implemented in either hardware or software. TCP/IP is implemented in Web software called server software (described below). TCP is the agreed upon protocol for transmitting data packets over the Web. TCP establishes the connections among sending and receiving Web computers, handles the assembly of packets at the point of transmission, and their reassembly at the receiving end.TCP/IP回答了在因特网上用信息包做什么和如何处理信息包的问题。TCP指传输控制协议,IP表示网际协议。协议是一组用于信息的格式化、次序化、压缩和检查错误的规则。它也可以限定传输速度和网上设备显示它们已停止发送及(或)接收信息的方法。协议既可以通过硬件也可通过软件来实现。TCP/IP(传输控制协议/网际协议)通过被称为服务器软件的网络软件来实现(在下文描述)。TCP(传输控制协议)是用来在网上传输数据的公认协议。TCP(传输控制协议)在发送和接收网络计算机之间建立连接,处理信息包在传输点的组装和在接收端的重新组装。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 360
  • 361. TCP/IP is divided into four separate layers, with each layer handling a different aspect of the communication problem. The Network Interface Layer is responsible for placing packets on and receiving them from the network medium, which could be a Local Area Network (Ethernet) or Token Ring Network, or other network technology. TCP/IP(传输控制协议/网际协议)被分为四个独立的层,由每层处理通信问题的一个不同方面。网络接口层负责信息包在网络媒体上的排列和接收,网络媒体可能是局域网(以太网)、令牌环形网或其他网络技术。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 361
  • 362. TCP/IP is independent from any local network technology and can adapt to changes in the local level. The Internet Layer is responsible for addressing, packaging, and routing messages on the Internet. The Transport Layer is responsible for providing communication with the application by acknowledging and sequencing the packets to and from the application. The Application Layer provides a wide variety of applications with the ability to access the services of the lower layers. Some of the best known applications are Hyper Text Transfer Protocol (HTTP), File Transfer Protocol (FTP), and Simple Mail Transfer Protocol (SMTP), all of which we will discuss later in this chapter.TCP/IP(传输控制协议/网际协议)独立于任何局部网络技术,并能适应在局部水平上的改变。因特网层负责信息的寻址、封装及其在因特网上的路线排定。通过对信息包去与来应用层的确认和排序,传送层负责为应用层提供通信。应用层为许多应用提供访问较低层服务的能力。一些众所周知的应用是超文本传输协议(HTTP)、文件传输协议(FTP)和简单邮件传输协议(SMTP),稍后我们将本章中讨论 8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 362
  • 363. IP Addresses. TCP handles the packetizing and routing of Internet messages. IP provides the Internet’s addressing scheme. Every computer connected to the Internet must be assigned an address—otherwise it cannot send or receive TCP packets. For instance, when you sign onto the Internet using a dial-up telephone modem, your computer is assigned a temporary address by your Internet Service Provider.IP地址。TCP(传输控制协议)处理因特网信息的分组化和传输路线排定。IP(网际协议)提供因特网的地址分配方案。每部连接到因特网的计算机必须分配一个地址,否则它不能够发送或接受TCP(传输控制协议)信息包。举例来说,当你在使用调制解调器拨号上网时,你的计算机由因特网服务提供商分配一个临时地址。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 363
  • 364. Internet addresses, known as IP addresses, are 32-bit numbers that appear as a series of four separate numbers marked off by periods, such as 201.61.186.227. Each of the four numbers can range from 0–255. This “dotted quad” addressing scheme contains up to 4 billion addresses (232). The leftmost number typically indicates the network address of the computer, while remaining numbers help to identify the specific computer within the group that is sending (or receiving ) a message.因特网地址,即众所周知的IP地址,是一个32位的数字,它以一串由园点隔开的四个数字出现,例如 201.61.186.227。四个数字中的每一个都在0-255范围内。这个“点分四元组”地址分配方案包含多达到40亿个地址(232)。最左边的那个数字指示计算机的网络地址,而其余的数字帮助识别正在发送(或接收)信息的团体里面一台特定的计算机。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 364
  • 365. The current version of IP is called Version 4, or IPv4. Because many large corporate and government domains have been given millions of IP addresses each (to accommodate their current and future work forces), and with all the new networks and new Internet-enabled devices requiring unique IP addresses being attached to the Internet, a new version of the IP protocol, called IPv6 is being adopted. This scheme contains 128-bit addresses, or about one quadrillion (1015).IP现在版本叫做第4版,或IPv4。因为许多大公司和政府在各自的域中已给定了数百万个IP地址(以适应他们当前和未来的劳动力),且由于新网络和新的可上网设备需要独特的IP地址,新版本IP协议IPv6正在得到采用。这个方案包含128位的地址,或曰大约1015个地址。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 365
  • 366. Domain Names and URLs. Most people cannot remember 32-bit numbers. IP addresses can be represented by a natural language convention called domain names. The domain name system (DNS) allows expressions such as cnet.com to stand for numeric IP addresses (cnet.com’s numeric IP is 216.200.247.134). Uniform resource locators (URLs), which are the addresses used by Web browsers to identify the location of content on the Web, also use domain names as part of the URL. A typical URL contains the protocol to be used when accessing the address, followed by its location. 域名和统一资源定位(URL)。大多数人记不住32位的数字。IP地址可由一个自然语言约定(称为域名)来表示。域名系统(DNS)允许像cnet.com这样的表达代表数值型IP地址(cnet.com 的数值型IP地址是(216.200.247.134)。统一的资源定位是网络浏览器用于识别网上内容位置的地址,也使用域名作为它的一部分。一个典型的网址包含访问地址时使用的协议,接着是它的位置。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 366
  • 367. Client/Server Computing. While packet switching exploded the available communications capacity and TCP/IP provided the communications rules and regulations, it took a revolution in computing to bring about today’s Internet and the Web. That revolution is called client/server computing and without it, the Web—in all its richness—would not exist. In fact, the Internet is a giant example of client/server computing in which over 70 million host server computers store Web pages and other content that can be easily accessed by nearly a million local area networks and hundreds of millions of client machines worldwide. 客户机/服务器计算技术。虽然分组交换使有效的通信能力激增,且TCP/IP协议提供了通信规则,在计算机技术中,发生了又一次革命才造就了今天的因特网和万维网。这次革命叫做客户机/服务器计算技术,没有它,万维网及其丰富信息将不会存在。事实上,因特网是客户机/服务器计算技术的一个巨大实例,其中,超过7000万部主机服务器计算机储存网页和其他内容,这些网页和内容能被全世界接近一百万个局域网和数亿台客户机容易地访问。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 367
  • 368. Client/server computing is a model of computing in which very powerful personal computers called clients are connected together in a network together with one or more server computers. These clients are sufficiently powerful to accomplish complex tasks such as displaying rich graphics, storing large files, and processing graphics and sound files, all on a local desktop or handheld device. Servers are networked computers dedicated to common functions that the client machines on the network need, such as storing files, software applications, utility programs such as Web connections, and printers. 客户机/服务器计算技术是一种计算模型,其中相当多台被称为客户机的个人计算机联结在一起并与一台或更多的服务器计算机联结在一个网络中。这些客户机功能足够强大以完成复杂的任务如显示丰富的图形、储存大型文件、并处理图形和声音文件,这些任务全部在当地的台式或手持式装置上完成。服务器是联网的计算机,专门用于提供客户机在网上需要的公共功能,例如储存文件、软件应用、公用程序如网络连接、和打印。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 368
  • 369. To appreciate what client/server computing makes possible, you must understand what preceded it. In the mainframe computing environment of the 1960s and 1970s, computing power was very expensive and limited. For instance, the largest commercial mainframes of the late 1960s had 128k of RAM and 10 megabyte disk drives, and occupied hundreds of square feet. There was insufficient computing capacity to support graphics or color in text documents, let alone sound files or hyper linked documents and databases.为了充分理解客户机/服务器计算技术的作用,你必须了解在它之前的东西。在20世纪60年代和70年代的大型计算机环境中,计算机能力非常昂贵而有限。比如,60年后期最大的商业化大型机有128K随机存取存储器和10兆磁盘驱动器,而且占据数百平方英尺空间。计算能力不足以支持图形和文本中的颜色,更不用说声音文件或超链接文档和数据库。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 369
  • 370. With the development of personal computers and local area networks during the late 1970s and early 1980s, client/server computing became possible. Client/server computing has many advantages over centralized mainframe computing. For instance, it is easy to expand capacity by adding servers and clients. Also, client/ server networks are less vulnerable than centralized computing architectures. If one server goes down, backup or mirror servers can pick up the slack; if a client machine is inoperable, the rest of the network continues operating. Moreover, processing load is balanced over many powerful smaller machines rather than being concentrated in a single huge machine that performs processing for everyone. Both software and hardware in client/server environments can be built more simply and economically.20世纪70年代后期和80年代初期,随着个人计算机和局域网的发展,客户机/服务器计算技术成为可能。客户机/服务器计算技术比中央大型机计算有许多优势。比如,通过增加服务器和客户机,可很容易地扩容。同时,客户机/服务器网络比中央计算结构不易受损。如果一个服务器被破坏,备用的或镜像服务器能恢复工作;如果一部客户机不能运转,网络的其部分可继续运行。而且, 负荷处理通过许多强大的、较小的机器达到平衡,而不是集中于一部为每个人进行处理的巨型机。在客户机/服务器环境中,建立软件与硬件都更简单、更经济。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 370
  • 371. Today there are about 450 million PCs in existence worldwide. Most of these PCs can display and process graphics, sound files, and colored text. They have memories up to 512MB, 20 gigabyte hard drives, and occupy about two square feet. These personal “supercomputers,” when tied together in local area networks or into large wide area networks such as the Web, make it possible for millions of people to enjoy “rich” Web documents and experiences. Soon these capabilities will move to handheld devices such as the Palms and HP Jornada, and wireless cell phones (much “thinner clients”). In the process, more computer processing will be performed by central servers (reminiscent of mainframe computers of the past).今天全世界大约有4.5亿台个人计算机,其中大多数可以显示并且处理图形、声音文件、和彩色文本。他们具有高达512MB内存、20G(兆字节)硬盘驱动器,而大约只占2平方英尺空间。这些个人的“超级计算机”,把它们联结起来接入局域网或大型广域网如因特网,使数以百万计的人们享受“丰富的”网络文件和经验成为可能。这些能力将很快会移植到如Palms、HP Jornada和无线蜂窝电话等手持式装置中(很多“瘦客户机”)。在这个过程中,更多的计算机处理将由中央服务器完成(过去的大型计算机的遗风)。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS 371
  • 372. There are many other Internet protocols that provide services to users in the form of Internet applications that run on Internet clients and servers. These Internet services are based on universally accepted protocols—or standards—that are available to everyone who uses the Internet. They are not owned by any one organization but are services that were developed over many years and given to all Internet users.有许多其他因特网协议以因特网应用的形式为用户提供服务,这些因特网应用在客户机和服务器上运行。这些因特网服务以全世界普遍承认的协议或标准为基础,对任何使用因特网的用户有效。他们不为任何一个组织所拥有,而是发展了许多年、供给所有因特网用户的服务。8.1.3 Other Internet Protocols And Utility Programs 372
  • 373. HTTP: Hypertext Documents. HTTP (short for Hyper Text Transfer Protocol) is the Internet protocol used for transferring Web pages (described in the following section). The HTTP protocol runs in the Application Layer of the TCP/IP model. An HTTP session begins when a client’s browser requests a Web page from a remote Internet server. When the server responds by sending the page requested, the HTTP session for that object ends. Because Web pages may have many objects on them—graphics, sound or video files, frames, and so forth—each object must be requested by a separate HTTP message.HTTP: 超文本文档。HTTP(超文本传输转移协议的缩写)是用于传输网页的因特网协议(下文描述)。HTTP协议在TCP/IP模型中的应用层上运行。当一个客户机的浏览器向远程因特网服务器的一个网页发出请求时,HTTP会话开始。当服务器通过发送所请求的页面回应时,关于这个对象的HTTP会话结束。因为网页可能带有许多对象——图形、声音或视频文件、帧等——每个对象必须由一个独立的HTTP 信息所请求。8.1.3 Other Internet Protocols And Utility Programs 373
  • 374. SMTP, POP, and IMAP: Sending E-mail. E-mail is one of the oldest, most important, and frequently used Internet services. STMP (Simple Mail Transfer Protocol) is the Internet protocol used to send mail to a server. POP (Post Office Protocol) is used by the client to retrieve mail from an Internet server. You can see how your browser handles SMTP and POP by looking in your browser’s Preferences or Tools section, where the mail settings are defined. SMTP、POP和IMAP:发送电子邮件。电子邮件是最老、最重要和经常使用的因特网服务之一。STMP(简单邮件传输协议)是用于将将邮件发送到服务器的因特网协议。客户机利用POP(邮局协议)从因特网服务器上检索邮件。你可以通过察看浏览器上“收藏”和“工具”栏看见你的浏览器如何处理SMTP和POP协议,邮件设定在这两栏定义。8.1.3 Other Internet Protocols And Utility Programs 374
  • 375. You can set POP to retrieve e-mail messages from the server and then delete the messages on the server, or retain them on the server. IMAP (Internet Message Access Protocol) is a more current e-mail protocol supported by many servers and all browsers. IMAP allows users to search, organize, and filter their mail prior to downloading it from the server.你可以设定用POP协议取回来自服务器的电子邮件信息然后删除服务器上的信息,或在服务器上保留它们。IMAP(因特网消息访问协议)是一个由许多服务器和所有的浏览器支持的更通用的电子邮件协议。IMAP允许使用者在从服务器下载邮件之前搜寻、组织和过滤邮件 8.1.3 Other Internet Protocols And Utility Programs 375
  • 376. FTP: Transferring Files. FTP (File Transfer Protocol) is one of the original Internet services. It is a part of the TCP/IP protocol and permits users to transfer files from the server to their client machine, and vice versa. The files can be documents, programs, or large database files. FTP is the fastest and most convenient way to transfer files larger than 1 megabyte, which many mail servers will not accept.FTP:传输文件。FTP(文件传输协议)是最初的因特网服务之一。它是TCP/IP协议的一部份,它允许用户把文件从服务器传送到客户机,反之亦然。文件可以是文档、程序、或大型数据库文件。FTP是传输大于1M文件最快速和最方便的方法,而许多邮件服务器将不接受大于1M的文件 8.1.3 Other Internet Protocols And Utility Programs 376
  • 377. SSL: Security. SSL (Secure Sockets Layer) is a protocol that operates between the Transport and Application Layers of TCP/IP and secures communications between the client and the server. SSL helps secure e-commerce communications and payments through a variety of techniques such as message encryption and digital signatures.SSL:安全性。SSL(加密套接字协议层)是一个在TCP/IP中运行于的传输层和应用层之间的、确保客户机与服务器之间通信安全的协议。通过诸如信息加密和数字签名等多种技术,SSL促进安全的电子商务通信和支付。8.1.3 Other Internet Protocols And Utility Programs 377
  • 378. Telnet: Running Remote. Telnet is a terminal emulation program that runs in TCP/IP. You can run Telnet from your client machine. When you do so, your client emulates a mainframe computer terminal. (The industry standard terminals defined in the days of mainframe computing are VT-52, VT-100, and IBM 3250.) You can then attach yourself to a computer on the Internet that supports Telnet and run programs or download files from that computer. Telnet was the first “remote work” program that permitted users to work on a computer from a remote location. Telnet(远程登录):远程运行。Telnet是一个在TCP/IP中运行的终端模拟程序。你能从你的客户机运行Telnet。当你这么做的时候,你的客户机模拟一个主机计算机终端。(定义于大型机计算时代的工业标准终端是VT-52、VT-100和IBM 3250)。然后你能接入到一台因特网上支持Telnet的计算机上,从那部计算机运行程序或下载文件。Telnet是允许用户在远方的一部计算机上工作的第一个“远程工作”程序。8.1.3 Other Internet Protocols And Utility Programs 378
  • 379. Finger: Finding People. You can find out who is logged onto a remote network by using Telnet to connect to a server, and then typing “finger” at the prompt. Finger is a utility program supported by UNIX computers. When supported by remote computers, finger can tell you who is logged in, how long they have been attached, and their user name. Obviously there are security issues involved with supporting finger, and most Internet host computers do not support finger today. Finger: 发现人们。通过使用Telnet连接到一个服务器上,然后在提示符的键入"Finger",你能发现谁登录到远程网络。Finger是一个UNIX 计算机支持的公用程。当由远程计算机支持时,Finger能告诉你谁登录了、他们已经连上多久和他们的用户名。显然,支持Finger会涉及安全问题,而且大多数因特网主机今天不支持Finger。 8.1.3 Other Internet Protocols And Utility Programs 379
  • 380. Ping: Testing the Address. You can “ping” a host computer to check the connection between your client and the server. The ping (Packet InterNet Groper) program will also tell you the time it takes for the server to respond, giving you some idea about the speed of the server and the Internet at that moment. You can run ping from the DOS prompt on a personal computer with a Windows operating system by typing: Ping .Ping:检测地址。你可以"Ping"一台主机计算机来检查你的客户机和服务器之间的连结。给出你有关服务器和因特网速度的一些建议,Ping(Packet InterNet Groper,信息包因特网搜索)程序还将会告诉你服务器回应所需的时间。你可以在一部具有Windows操作系统的个人计算机上在DOS提示符下键入:Ping<域名>。8.1.3 Other Internet Protocols And Utility Programs 380
  • 381. Tracert: Checking Routes. Tracert is one of a several route-tracing utilities that allow you to follow the path of a message you send from your client to a remote computer on the Internet. Tracert:检查路径。Tracert是几种追踪路径的公用程序之一,它允许你跟踪你在因特网上从客户机向远程计算机发出的信息的路径。8.1.3 Other Internet Protocols And Utility Programs 381
  • 382. New Words & Expressions substrate n. 衬底,基底 middleware n.中间设备,中间件 authentication n.证明, 鉴定 repository n. 储存库,资料档案库 backbone n.主干,干线 pipeline n. 流水线,管线 Mbps n. 兆比特每秒 Gbps n. 千兆比特每秒 redundancy n.冗余 built-in adj.内置的, 嵌入的n.内置 tier n.一层,一排 curb n.路边 mom and pop shop n. 夫妻店 dial-up 拨号上网 narrowband n. 窄带 broadband n. 宽带 throughput n. 吞吐量 objectionable adj.该反对的,不能采用的 modem n.调制解调器 delay n.延迟 aficionado n. 狂热爱好者, 迷 sovereign adj.统治的; n.统治者 Intranet 企业内部互联网 Extranets 企业外部互联网 piggyback n.机载 ; v.搭载8.2 The Internet Today382
  • 383. Abbreviations NAP (Network Access Point) 网络访问节点 DSL (digital subscriber line) 数字用户线 Metropolitan Area Exchange (MAE) 城域交换站 W3C (World Wide Web Consortium) 万维网联合会 ISP (Internet Service Provider) Internet服务提供者 ISOC (Internet Society) Internet 协会 IAB (Internet Architectrue Board) Internet架构委员会 IETF (Internet Engineering Task Force) Internet工程任务组 IESG (Internet Engineering Steering Group) Internet工程指导组8.2 The Internet Today383
  • 384. By 2001, there were approximately 400 million Internet users worldwide, up from 100 million users at year-end 1997. That figure is projected to continue to grow to close to 800 million by 2003. One would think that with such incredible growth, the Internet would be overloaded. However, this has not been true for several reasons. First, client/server computing is highly extensible: By simply adding servers and clients, the population of Internet users can grow indefinitely. Second, the Internet architecture is built in layers so that each layer can change without disturbing developments in other layers. For instance, the technology used to move messages through the Internet can go through radical changes to make service faster without being disruptive to your desktop applications running on the Internet.截至2001年,全世界因特网用户从1997年底的1亿上升到大约有4亿。这个数字计划到2003年继续增长到8亿。有人可能会想:以如此令人难以置信的速度增长,因特网会超载。然而,由于几个原因这没有成为现实。首先,客户机/服务器计算技术可以高度扩展:只需增加服务器和客户机,因特网用户人口能无限增长。其次,因特网是按照层次结构建造的,因此每一层能在不干扰其他层发展的前提下改变。举例来说,用于在因特网上移动信息的技术可以实现根本的改变使服务更快,而不会中断你的台式机在因特网上运行的应用。8.2 The Internet Today384
  • 385. The Internet can be viewed conceptually as having four layers: the network technology substrate, transport services and representation standards, middleware services, and applications. The network technology substrate is composed of telecommunications networks and protocols. The transport layer houses the TCP/IP protocol. The applications layer contains client applications such as the World Wide Web, e-mail, and audio or video playback. Middleware is the glue that ties the applications to the communications networks, and includes such services as security, authentication, addresses, and storage repositories. 因特网能被概念性地分为四层:网络技术基体、传送服务和表示标准、中间件服务和应用。网络技术基体由电信网络和协议组成。传送层收容TCP/IP协议。应用层包含客户机的应用,例如万维网、电子邮件和声频或视频回放。中间件是将应用与通信网络连接起来的粘合剂,并且包括如安全、验证、地址和存储等服务。8.2 The Internet Today385
  • 386. Users work with applications (such as e-mail) and rarely become aware of middleware that operates in the background. Because all layers use TCP/IP and other common standards linking all four layers, it is possible for there to be significant changes in the network layer without forcing changes in the applications layer. The network layer is described below.用户通过应用程序(例如电子邮件)工作,很少知道中间件在后台运行。因为各层使用TCP/IP协议和其他公共标准联结所有四层,所以在网络层发生重大变化而不强迫应用层变化是可能的。网络层在下面描述。8.2 The Internet Today386
  • 387. Figure 8-3 Internet I network architecture387
  • 388. 8.2.1 THE INTERNET BACKBONE Figure 8-3 illustrates the main physical elements of today’s Internet. The Internet’s backbone is formed by Network Service Providers (NSPs), which own and control the major networks. The backbone has been likened to a giant pipeline that transports data around the world in milliseconds. In the United States, the backbone is composed entirely of fiber-optic cable (described more fully below), with bandwidths ranging from 155 Mbps to 2.5 Gbps. Bandwidth measures how much data can be transferred over a communications medium within a fixed period of time, and is usually expressed in bits per second (bps), kilobits (thousands of bits) per second (Kbps), megabits (millions of bits) per second (Mbps), or gigabits (billions of bits) per second (Gbps).图8-3说明了今天因特网的主要物理组成。因特网主干由拥有且控制主要网络的网络服务提供商(NSPs)形成。主干被比作一个能在几毫秒内将数据传遍全球的巨大通道。在美国,主干完全由光缆(在文下更完整地描述)组成,其带宽从155兆比特/秒到2.5吉比特/秒。带宽衡量在固定的时间内、通过某种通信媒体能传输多少数据,通常以每秒位(bps)、每秒千位 (Kbps)、每秒兆位(Mbps)或每秒千兆位(Gbps)来表示。 388
  • 389. Connections to other continents are made via a combination of undersea fiber optic cable and satellite links. The backbones in foreign countries typically are operated by a mixture of private and public owners. The U.S. backbone is one of the most developed because the Internet’s infrastructure was developed here. The backbone has built-in redundancy so that if one part breaks down, data can be rerouted to another part of the backbone. Redundancy refers to multiple duplicate devices and paths in a network.与其他大陆的连接是经由海底光缆和人造卫星联通的。在外国,因特网主干是由私营和国有公司共同经营的。美国的因特网主干是(全世界)最发达的(主干)之一,因为因特网的基础是从这里发展起来的。因特网主干具有内在的冗余,以便如果主干的一部分崩溃,数据可以改行其他部份。冗余指在网络中设备和路径的多重副本。8.2.1 THE INTERNET BACKBONE 389
  • 390. In the United States there are a number of hubs where the backbone intersects with regional and local networks, and where the backbone owners connect with one another1. These hubs are called Network Access Points (NAPs) or Metropolitan Area Exchanges (MAEs), and use high-speed switching computers to connect the backbone to regional and local networks, and exchange messages with one another. The regional and local networks are owned by local Bell operating companies (RBOCs—pronounced “ree-bocks”), and private telecommunications firms such as MFS Corporation; they generally are fiber optic networks operating at over 100 Mbps. The regional networks lease access to Internet Service Providers, private companies, and government institutions.在美国,有许多网络中心——因特网主干与区域性和地方性网络在此交叉,主干拥有者也在此处彼此连接。这些网络中心被称为网络访问节点(NAP)或城域交换站(MAE),而且它们使用高速交换计算机联结主干与地方性和区域性网络、并彼此交换信息。区域性和地方性网络由地方贝尔运营公司(RBOCs-发音 "ree-bocks")和私营电信公司例如MFS公司所拥有;它们通常是以超过100Mbps带宽运行的光纤网络。区域性网络从因特网服务提供商、私营公司和政府机构租用使用权。8.2.2 Network access points and metropolitan area exchanges 390
  • 391. The Internet backbone connects regional networks, which in turn provide access to the Internet to Internet Service Providers, large firms, and government agencies.因特网主干连接区域性网络,这些区域性网络反过来为因特网服务提供商、大公司和政府机关提供对的因特网的访问。8.2.2 Network access points and metropolitan area exchanges 391
  • 392. 8.2.3 CAMPUS NETWORKSThere are an estimated one million campus networks attached to the Internet worldwide (Computer Industry Almanac Inc., 2001). Campus networks are generally local area networks operating with a single organization— such as New York University or Microsoft Corporation. In fact, most large organizations have hundreds of such local area networks. These organizations (representing about 60 million workers) are sufficiently large that they lease access to the Web directly from regional and national carriers. These local area networks generally are running Ethernet (a local area network protocol) and have operating systems such as Windows 2000 (NT), Novell, or others that permit desktop clients to connect to the Internet through a local Internet server attached to their campus networks. Connection speeds in campus networks are in the range of 10–100 Mbps to the desktop.估计全世界有100万个校园网联结到因特网(计算机工业年间鉴公司,2001年)。校园网通常是一个组织运营的局域网,例如纽约大学或微软公司。事实上,大部分大组织有几百个这样的局域网。这些组织(代表大约6亿工人)足够大,以至于他们直接向区域性和国家通信公司租用对网络的访问。这些局域网通常是运行的以太网(一种局域网协议),并且具有例如Windows2000(NT)、Novell或其他操作系统,允许桌面客户机通过一个连接到校园网的因特网服务器联到因特网。在校园网中,台式机的连接速度在10-100 Mbps。392
  • 393. 8.2.4 INTERNET SERVICE PROVIDERSThe firms that provide the lowest level of service in the multi-tiered Internet architecture by leasing Internet access to home owners, small businesses, and some large institutions are called Internet Service Providers (ISPs)2. ISPs are retail providers—they deal with “the last mile of service” to the curb, the home, the business office. About 45 million American households connect to the Internet through either national or local ISPs. ISPs typically connect to the Internet and MAEs or NAPs with high-speed telephone or cable lines (up to 45 Mbps).在多层次因特网体系中通过向家庭出租因特网访问通道提供最低水平服务的公司、小型企业,和一些大机构叫做因特网服务提供商(ISP)。因特网服务提供商是零售型供给者——他们为街头、家庭、企业办公室处理“最后一步服务”。约4500万个美国的家庭通过全国性的或地方性的ISP连接到因特网。因特网服务提供商又利用高速电话或电缆线(高达45 Mbps)典型地连接到因特网和城域交换站或网络访问节点。 393
  • 394. There are two types of ISP service: narrowband and broadband. Narrowband service is the traditional telephone modem connection now operating at 56.6 Kbps (although the actual throughput hovers around 30 Kbps due to line noise that causes extensive resending of packets). This is the most common form of connection worldwide. Broadband service is based on DSL, cable modem, telephone (T1 and T3 lines), and satellite technologies. Broadband—in the context of Internet service —refers to any communication technology that permits clients to play streaming audio and video files at acceptable speeds—generally anything above 100 Kbps.因特网服务提供商提供两种服务:窄带和宽带。窄带服务是目前以56.6 Kbps运行的传统电话调制解调器连接(虽然由于线路噪音造成大量的信息包重新发送,真正的吞吐量徘徊在30Kbps附近)。这是全世界最普通的联结形式。宽频服务以数字用户专线、电缆调制解调器,电话(T1和T3线)和人造卫星技术为基础。在因特网服务的环境中,宽频指的是任何允许客户机以可接受的速度运行流型声频和视频文件的通信技术,通常可接受的速度指在100 Kbps以上。8.2.4 INTERNET SERVICE PROVIDERS394
  • 395. The term DSL refers to digital subscriber line service, which is a telephone technology for delivering high-speed access through ordinary telephone lines found in your home or business. Service levels range from about 150 Kbps all the way up to 1 Mbps. DSL service requires that customers live within two miles (about 4,000 meters) of a neighborhood telephone switching center.术语DSL指数字用户专线服务,是通过在你家或企业所见到的普通电话线传送高速访问的一种电话技术。服务水平从大约从150Kbps到高达1Mbps。数字用户专线服务要求客户居住在临近电话交换中心2英里之内(大约4000米)。8.2.4 INTERNET SERVICE PROVIDERS395
  • 396. Cable modem refers to a cable television technology that piggybacks digital access to the Internet on top of the analog video cable providing television signals to a home3. Cable modem services ranges from 350 Kbps up to 1 Mbps. Cable service may degrade if many people in a neighborhood log on and demand high-speed service all at once. 电缆调制解调器是一种在向家庭提供电视信号的视频电缆上搭载对因特网进行数字式访问的有线电视技术。电缆调制解调器服务范围从350 Kbps到1Mbps。如果临近有许多人同时登录并需要高速服务,缆传服务速度可能降低。8.2.4 INTERNET SERVICE PROVIDERS396
  • 397. T1 and T3 are international telephone standards for digital communication. T1 lines offer guaranteed delivery at 1.54 Mbps, while T3 lines offer delivery at 43 Mbps. T1和T3是数字通信的国际电话标准。T1线提供保障1.54Mbps的传送,而T3线提供43Mbps传送。8.2.4 INTERNET SERVICE PROVIDERS397
  • 398. 8.2.5 INTRANETS AND EXTRANETSThe very same Internet technologies that make it possible to operate a worldwide public network can also be used by private and government organizations as internal networks. An intranet is a TCP/IP network located within a single organization for purposes of communications and information processing. Many corporations are moving away from proprietary local area networks such as Windows 2000 and Novell, and toward a single internal intranet to handle the firm’s information processing and communication needs. Internet technologies are generally far less expensive than proprietary networks, and there is a global source of new applications that can run on intranets. In fact, all the applications available on the public Internet can be used in private intranets.. 使全球性公众网络运转成为可能的、与因特网技术相同的技术也能被私营和政府组织用于内部网络。内联网是一个组织内部用于通信和信息处理的TCP/IP网络。许多公司正在远离专有局域网例如Windows 2000和Novell,并转向一个单一的企业内联网以处理公司的信息和通信需要。因特网技术通常远比专有网络技术价廉,而且拥有一个全球资源获得可在内联网上运行的新应用。事实上,在公用因特网上得到的所有应用都能在专用内联网使用。398
  • 399. 8.2.5 INTRANETS AND EXTRANETSExtranets are formed when firms permit outsiders to access their internal TCP/IP networks. For instance, General Motors permits parts suppliers to gain access to GM’s intranet that contains GM’s production schedules4. In this way, parts suppliers know exactly when GM needs parts, and where and when to deliver the parts. 当公司允许局外人访问他们的内部TCP/IP网络时,外联网就形成了。举例来说,通用汽车公司允许零部件供应商访问公司的内联网,它的内联网包含生产进度。这样,零部件供应商能完全了解通用汽车公司什么时候需要零部件,和到哪里与何时递送零部件。399
  • 400. 8.2.6 WHO GOVERNS THE INTERNET?Aficionados and promoters of the Internet often claim that the Internet is governed by no one, and indeed cannot be governed, and that it is inherently above and beyond the law. In fact, the Internet is tied into a complex web of governing bodies, national legislatures, and international professional societies. There is no one governing body that controls activity on the Internet. Instead, there are several organizations that influence the system and monitor its operations. Among the governing bodies of the Internet are:因特网的热爱者和促进者时常宣称因特网没有被任何人统治,也的确不能被统治,而且还宣称它天生高于法律。事实上,因特网被连入了由管理机构、国家立法机构和国际专业协会织成的一张复杂的网之中。没有一个管理机构可以控制因特网上的活动,而是有几个组织影响它的系统、监测它的运行。在因特网管理机构中有:400
  • 401. 8.2.6 WHO GOVERNS THE INTERNET?The Internet Architecture Board (IAB), which helps define the overall structure of the Internet. The Internet Corporation for Assigned Names and Numbers (ICANN), which assigns IP addresses, and the Internet Network Information Center (InterNIC), which assigns domain names. The Internet Engineering Steering Group (IESG), which oversees standard setting with respect to the Internet. 因特网架构委员会(IAB)帮助定义因特网的总体结构。 因特网域名与地址管理委员会(ICANN)分配IP地址;和因特网网络信息中心(InterNIC)分配域名。 因特网工程指导组(IESG)监督有关因特网的标准设定。 401
  • 402. 8.2.6 WHO GOVERNS THE INTERNET?The Internet Engineering Task Force (IETF), which forecasts the next step in the growth of the Internet, keeping watch over its evolution and operation. The Internet Society (ISOC), which is a consortium of corporations, government agencies, and nonprofit organizations that monitors Internet policies and practices. The World Wide Web Consortium (W3C), which sets HTML and other programming standards for the Web.因特网工程任务组(IETF)预测因特网成长的下一步,监视它的进化和运行。 因特网协会(ISOC)是一个公司、政府机关以及监测因特网政策与实践的非营利性组织的联盟。 万维网联合会(W3C)为万维网设定HTML和其他编程标准。402
  • 403. 8.2.6 WHO GOVERNS THE INTERNET?While none of these organizations has actual control over the Internet and how it functions, they can and do influence government agencies, major network owners, ISPs, corporations, and software developers with the goal of keeping the Internet operating as efficiently as possible.尽管这些组织中没有一个能真正控制因特网及其如何运行,他们可以就保持因特网尽可能高效运行的目标影响政府机关、主要网络拥有者、公司、因特网服务提供商和软件开发者。403
  • 404. 8.2.6 WHO GOVERNS THE INTERNET?In addition to these professional bodies, the Internet must also conform to the laws of the sovereign nation-states in which it operates, as well as the technical infrastructures that exist within the nation-state. Although in the early years of the Internet and the Web there was very little legislative or executive interference, this situation will change in the near future as the Internet plays a growing role in the distribution of information and knowledge, including content that some find objectionable 除了这些专业团体,因特网还必须符合所在的主权民族国家的法律,和这个民族国家存在的技术基础。虽然因特网和万维网在早年很少受到司法与或行政干涉,这种情形在不久的将来就会改变,因为因特网在传播信息和知识方面扮演越来越重要的角色,包括一些有人反对的内容。404
  • 405. New Words & Expressions congestion n.阻塞 appreciate vt. 领会,鉴赏, 感激,察觉 circuitous adj.迂回线路的 latency n.等待时间 streaming adj.流型的; n.流 synchronous adj.同时的, 同步的 jerkiness n.不平稳,颠簸 tag n. 标志,特征,标记[识];标识符 multicasting 多信道广播 diffserve 区别质量的服务 videoconference n.视频会议 Abbreviations AOL (American On-Line) 美国在线服务公司 NASA (National Aeronautics and Space Administration) (美国)国家航空航天局8.3 Internet II: The Future Infrastructure 405
  • 406. Much of the Internet’s current infrastructure is several decades old (equivalent to a century in Internet time). It suffers from a number of limitations, including: Bandwidth limitations. There is insufficient capacity throughout the backbone, the metropolitan switching centers, and most importantly, to the “last mile” to the house and small business. The result is slow service (congestion) and a very limited ability to handle video and voice traffic.许多因特网现在的基础设施是几十年以前的(在因特网时代等于一个世纪)。它承受许多限制,包括: 带宽限制。在主干、城市交换中心和最重要的最终对家庭和小型企业都存在着容量不足的问题。其结果是极慢的服务(阻塞)和相当有限的处理音频、视频的能力。8.3.1 LIMITATIONS OF INTERNET I406
  • 407. Quality of service limitations. Today’s information packets take a circuitous route to get to their final destinations. This creates the phenomenon of latency— delays in messages caused by the uneven flow of information packets through the network. In the case of e-mail, latency is not noticeable. However, with streaming video and synchronous communication, such as a telephone call, latency is noticeable to the user and perceived as “jerkiness” in movies or delays in voice communication. Today’s Internet uses “best efforts” quality of service, (QOS), which makes no guarantees about when or whether data will be delivered, and provides each packet with the same level of service, no matter who the user is or what type of data is contained in the packet. A higher level of service quality is required if the Internet is to keep expanding into new services (such as video on demand or telephony).服务品质限制。今天的信息包需经过迂回路径到达目的地。这就产生了等待时间的现象——由于信息包通过网络时流动不畅通引起的信息延迟。就电子邮件来说,等待时间不引人注目。然而对于视频流和同步通信例如电话呼叫,等待时间对使用者是显而易见的并且在电影中感觉到"抖动"或在声音通信中感到延迟。今天的因特网使用"最大努力"的服务品质,对数据何时或是否被递送没有任何保证;而且无论使用者是谁或信息包中包含什么类型的数据,提供每个信息包相同水平的服务。如果因特网要继续扩大新的服务,就需要较高水平的服务质量(例如随选视频服务或声音传送)。8.3.1 LIMITATIONS OF INTERNET I407
  • 408. Network architecture limitations. Today, a thousand requests for a single music track from a central server will result in a thousand efforts by the server to download the music to each requesting client. This slows down network performance as the same music track is sent out a thousand times to clients that might be located in the same metropolitan area. This is very different from television, where the program is broadcast once to millions of homes. 网络结构限制。今天,对来自一个中央服务器的一个音乐辑发出一千个请求,将会造成服务器为每个请求的客户机下载音乐而动作一千次。当同一个音乐辑被送出一千次到可能位于相同城区的客户机,就减慢了网络性能。这非常不同于电视,电视节目一次对数以百万计的家庭广播。 8.3.1 LIMITATIONS OF INTERNET I408
  • 409. Language development limitations. HTML, the language of Web pages, is fine for text and simple graphics, but poor at defining and communicating “rich documents” such as databases, business documents, or graphics. The tags used to define an HTML page are fixed and generic.语言发展限制。HTML网页语言,对本文和简单的图形是好的,但在定义和传递如数据库、商业文件或图形等"富文件"时是不够的。用于定义HTML页的标签是固定的和通用的。8.3.1 LIMITATIONS OF INTERNET I409
  • 410. Now imagine an Internet at least 100 times as powerful as today’s Internet, an Internet not subjected to the limitations of bandwidth, protocols, architecture, and language detailed above. Welcome to the world of Internet II, and the next generation of e-commerce services and products.现在想象一下因特网的功能至少是现在的100倍,想象一下一个不受上述带宽、协议、结构和语言限制的因特网。欢迎你到因特网II的世界和下一代电子商务服务与产品的世界。8.3.1 LIMITATIONS OF INTERNET I410
  • 411. The increased bandwidth and expanded network connections of the Internet II era will result in benefits beyond faster access and richer communications. Enhanced reliability and quality of Internet transmissions will create new business models and opportunities. Some of the major benefits of these technological advancements include IP multicasting, latency solutions, guaranteed service levels, lower error rates, and declining costs.因特网II时代增加的带宽与扩大的网络连接造就的利益不只是更快的访问和更丰富的通信。因特网传输的可靠性与质量的提高将会造就新的商业模型和机会。这些技术进步的一些主要的益处包括IP多信道广播、等待时间解决方案、有保证的服务水平、低错误率和成本的降低。8.3.3 The larger Internet II technology environment 411
  • 412. IP Multicasting. IP multicasting is a set of technologies that enables efficient delivery of data to many locations on a network. Rather than making multiple copies of a message intended to be distributed to multiple recipients at the point of origin of a message, multicasting initially sends just one message and does not copy it to the individual recipients until it reaches the closest common point on the network, thereby minimizing the bandwidth consumed. Network performance is significantly improved because it isn’t bogged down with the processing and transmission of several large data files; each receiving computer doesn’t have to query the transmitting server for the file. IP多信道广播。IP多信道广播是使一组数据向网络中许多位置高效递送的技术。不是将一个信息在源点复制多份向多个接收者分配,多信道广播开始时只是发出一份信息而不向接收者复制,直到它到达网络上最近的公共点,因此使消耗的带宽最少。因为它不会因处理和传输一些大的数据文件陷入停顿,所以网络型能大大地被改良;每个接收计算机不必为一个文件向传输服务器发出请求。8.3.3 The larger Internet II technology environment 412
  • 413. Latency Solutions. One of the challenges of packet switching, where data is divided into chunks and then sent separately to meet again at the destination, is that the Internet does not differentiate between high-priority packets, such as video clips, and those of lower priority, such as self-contained e-mail messages. Because the packets cannot yet be simultaneously reassembled, the result is distorted audio and video streams.等待时间解决方案。将数据分为多块、然后分开传送以便到目的地后再集合的分组交换技术,面临的挑战之一是因特网不区别高优先权信息包如图像修剪,与低优先权信息包如自我包容的电子邮件信息。因为信息包不能然同时重新装配,结果导致声频与视频流失真。8.3.3 The larger Internet II technology environment 413
  • 414. Internet II, however, holds the promise of diffserve, or differentiated quality of service—a new technology that assigns levels of priority to packets based on the type of data being transmitted. Videoconference packets, for example, which need to reach their destination almost instantaneously, would receive much higher priority than e-mail messages. In the end, the quality of video and audio will skyrocket without undue stress on the network. Live and on-demand TV and video will be possible once Internet II is completed.然而因特网II承诺区别服务品质——一种以被传输的数据类型为基础、为信息包分配优先权等级的新技术。例如,视讯会议信息包需要几乎即时到达目的地,将接受比电子邮件信息高的多的优先权。最后,由于在网上没有了过度的压力,视频和声频的质量将猛涨。一旦因特网II完成,实况和随选电视与视频将成为可能。8.3.3 The larger Internet II technology environment 414
  • 415. Guaranteed Service Levels. In today’s Internet, there is no service-level guarantee and no way to purchase the right to move data through the Internet at a fixed pace. The Internet is democratic—it speeds or slows everyone’s traffic alike. With Internet II, it will be possible to purchase the right to move data through the network at a guaranteed speed in return for higher fees.有保证的服务水平。在今天的因特网中,没有任何服务水平保证也没有办法购买以固定速度通过因特网移动数据。因特网是民主的——它加速或减慢每个人的通信量。通过因特网II,将可购买以有保障的速度经过网络移动数据的权利,作为对较高费用的回报。8.3.3 The larger Internet II technology environment 415
  • 416. Lower Error Rates. Improved capacity and packet switching will inevitably impact quality of data transmissions, reducing error rates and boosting customer satisfaction. 更低的错误率。改进的能力和分组交换不可避免地影响数据传输的质量,减少错误率而提高客户满意度。 8.3.3 The larger Internet II technology environment 416
  • 417. Declining Costs. As the Internet pipeline is upgraded, the availability of broadband service will expand beyond major metropolitan areas, significantly reducing the costs of access. More users means lower cost, as products and technology catch on in the mass market. Higher volume usage enables providers to lower the cost of both access devices, or clients, and the service required to use such products. Both broadband and wireless service fees are expected to decline as geographic service areas increase, in part due to competition for that business.费用的降低。由于因特网通道升级,宽频服务的有效性将会超过主要大城市的范围,大大地降低访问的费用。较多的使用者意味比较低的费用,如同产品和技术在大众的市场中流行一样。较多的使用准许供应商降低访问设备或客户机的费用和服务必需使用的此类产品费用。随着服务的地理区域增大,预计宽频和无线服务的费用都将降低,部份是由于商业竞争。8.3.3 The larger Internet II technology environment 417
  • 418. 英语长句的翻译一、英语长句的分析 一般来说, 造成长句的原因有三方面: (1) 修饰语过多;(2) 并列成分多; (3)语言结构层次多。 在分析长句时可以采用下面的方法: 找出全句的主语、谓语和宾语, 从整体上把握句子的结构。 找出句中所有的谓语结构、非谓语动词、介词短语和从句的引导词。 分析从句和短语的功能, 例如, 是否为主语从句, 宾语从句, 表语从句等,若是状语,它是表示时间、原因、结果、还是表示条件等等。 分析词、短语和从句之间的相互关系, 例如, 定语从句所修饰的先行词是哪一个等。 注意插入语等其他成分。 注意分析句子中是否有固定词组或固定搭配。418
  • 419. 一、英语长句的分析例. For a family of four, for example, it is more convenient as well as cheaper to sit comfortably at home, with almost unlimited entertainment available, than to go out in search of amusement elsewhere. 分析: (1) 该句的骨干结构为it is more … to do sth than to do sth else.是一个比较结构, 而且是在两个不定式之间进行比较。(2) 该句中共有三个谓语结构, 它们之间的关系为: it is more convenient as well as cheaper to … 为主体结构, 但it是形式主语, 真正的主语为第二个谓语结构: to sit comfortably at home, 并与第三个谓语结构to go out in search of amusement elsewhere作比较。(3) 句首的for a family of four作状语, 表示条件。另外, 还有两个介词短语作插入语: for example, with almost unlimited entertainment available,其中第二个介词短语作伴随状语, 修饰to sit comfortably at home. [译文]譬如, 对于一个四口之家来说, 舒舒服服地在家中看电视, 就能看到几乎数不清的娱乐节目, 这比到外面别的地方去消遣又便宜又方便。419
  • 420. 二、英语长句的翻译 英语习惯于用长的句子表达比较复杂的概念, 而汉语则不同,常常使用若干短句, 作层次分明的叙述。因此, 在进行英译汉时,要特别注意英语和汉语之间的差异, 将英语的长句分解, 翻译成汉语的短句。在英语长句的翻译过程中, 我们一般采取下列的方法。1、顺序法。 当英语长句内容的叙述层次与汉语基本一致时, 可以按照英语原文的顺序翻译成汉语。 例. Even when we turn off the beside lamp and are fast asleep, electricity is working for us, driving our refrigerators, heating our water, or keeping our rooms air-conditioned. 分析: 该句子由一个主句, 三个作伴随状语的现在分词以及位于句首的时间状语从句组成, 共有五层意思: A.既使在我们关掉了床头灯深深地进入梦乡时; B.电仍在为我们工作; C. 帮我们开动电冰箱; D. 加热水; E.或是室内空调机继续运转。上述五层意思的逻辑关系以及表达的顺序与汉语完全一致, [译文]即使在我们关掉了床头灯深深地进入梦乡时, 电仍在为我们工作: 帮我们开动电冰箱, 把水加热, 或使室内空调机继续运转。420
  • 421. 二、英语长句的翻译2、逆序法 英语有些长句的表达次序与汉语表达习惯不同, 甚至完全相反, 这时必须从原文后面开始翻译。 例. For our purposes we will say e-commerce begins in 1995, following the appearance of the first banner advertisements placed by ATT, Volvo, Sprint and others on Hotwired.com in late October 1994, and the first sales of banner ad space by Netscape and Infoseek in early 1995. [译]伴随着ATT、Volvo、Sprint等公司所做的第一例横幅广告于1994年10月下旬出现在Hotwired.com上,和1995年初Netscape与Infoseek领先出售横幅广告空间,我们会说电子商务是从1995年开始的。421
  • 422. 二、英语长句的翻译3、分句法 有时英语长句中主语或主句与修饰词的关系并不十分密切, 翻译时可以按照汉语多用短句的习惯, 把长句的从句或短语化成句子,分开来叙述,为了使语意连贯, 有时需要适当增加词语。 例. The number of the young people in the United States who can't read is incredible about one in four. 上句在英语中是一个相对简单的句子, 但是如果我们按照原文的句子结构死译, 就可能被翻译成:“没有阅读能力的美国青年人的数目令人难以置信约为1/4。”这样, 就使得译文极为不通顺, 不符合汉语的表达习惯, 因此, 我们应该把它译为: [译文]大约有1/4的美国青年人没有阅读能力, 这简直令人难以置信。422
  • 423. 二、英语长句的翻译4、综合法 事实上,在翻译一个英语长句时, 并不只是单纯地使用一种翻译方法,而是要求我们把各种方法综合使用, 这在我们上面所举的例子中也有所体现。尤其是在一些情况下,一些英语长句单纯采用上述任何一种方法都不方便, 这就需要我们的仔细分析, 或按照时间的先后, 或按照逻辑顺序, 顺逆结合,主次分明地对全句进行综合处理,以便把英语原文翻译成通顺忠实的汉语句子。 例. Napster.com, which was established to aid Internet users in finding and sharing online music files known as MP3 files, is perhaps the most wellknown example of peer-to-peer e-commerce, although purists note that Napster is only partially peer-to-peer because it relies on a central database to show which users are sharing music files. 译文:Napster.com建立的目标是帮助因特网用户发现并分享在线音乐文件,即人所共知的MP3文件。尽管纯化论者强调:因为它依赖中央数据库来显示哪一位用户正在分享音乐文件,所以Napster仅仅是部分对等。但Napster或许是对等电子商务最著名的实例。423
  • 424. Computer EnglishChapter 9 The World Wide Web
  • 425. 理解万维网(World Wide Web)的工作原理; 能够描述Internet和万维网的特征及其服务; 了解学术论文写作的有关知识。Requirements:425
  • 426. The invention of the Web brought an extraordinary expansion of digital services to millions of amateur computer users, including color text and pages, formatted text, pictures, animations, video, and sound. In short, the Web makes nearly all the rich elements of human expression needed to establish a commercial marketplace available to nontechnical computer users worldwide.万维网的发明带来了为数以百万计的业余计算机使用者提供的数字化服务的非常扩展,包括彩色文本和网页、格式化文本、图片、动画、视频和声音。简而言之,万维网使建立商业化市场必需的人类表达方式的几乎所有丰富要素对非技术计算机使用者成为可能。426
  • 427. New Words & Expressions animation n. 动画 browse v.n.浏览 Hypertext n. 超文本 protocol n. 草案, 协议 extension n.扩展名 supplant vt.排挤掉, 代替 browser n 浏览器 surf vi.作冲浪运动, vt.在...冲浪 extension n.扩展名 supplant vt.排挤掉, 代替 browser n 浏览器 surf vi.作冲浪运动, vt.在...冲浪 Netscape 美国Netscape公司,以开发Internet浏览器闻名Abbreviations GML (Generalized Markup Language) 通用置标语言 SGML (Standard Generalized Markup Language) 标准通用置标语言 XML (Extensible Markup Language) 可扩展链接标示语言 SSL (Security Socket Layer) 加密套接字协议层 FTP (File Transfer Protocol) 文件传输协议 PDA (personal digital assistant) 个人数字助理 427
  • 428. 9.1 HYPERTEXTWeb pages can be accessed through the Internet because the Web browser software operating your PC can request Web pages stored on an Internet host server using the HTTP protocol. Hypertext is a way of formatting pages with embedded links that connect documents to one another, and that also link pages to other objects such as sound, video, or animation files. When you click on a graphic and a video clip plays, you have clicked on a hyperlink. 因为操作个人计算机的网络浏览器软件能使用HTTP协议对储存在因特网主机服务器上的一个网页发出请求,所以能通过因特网访问万维网网页。超文本是使用嵌入式链接形成格式化网页的一种方法,这些链接将文档彼此联结,而且将网页链接到其他对象如声音、视频或动画文件。当你点击一个图形和一个视频剪辑播放按钮的时候,你在点击一个超链接。428
  • 429. HTTP is the first set of letters at the start of every Web address, followed by the domain name. The domain name specifies the organization’s server computer that is housing the document. Most companies have a domain name that is the same as or closely related to their official corporate name. The directory path and document name are two more pieces of information within the Web address that help the browser track down the requested page. Together, the address is called a Uniform Resource Locator, or URL. When typed into a browser, a URL tells it exactly where to look for the information. HTTP是每个网址的第一个字母组合,位于网址的起始位置,紧跟着它的是域名。域名指定组织的服务器计算机,而文件收藏于服务器计算机之上。大多数公司有一个与其官方公司名字相同或接近的域名。目录路径和文件名在网址中是出现较多的两个信息,它帮助浏览器捕捉被请求的网页。同时,网址叫做统一资源定位符,或URL。当把网址键入一个浏览器内时,URL准确分辨到哪里找寻数据。 9.1 HYPERTEXT429
  • 430. Although the most common Web page formatting language is HTML, the concept behind document formatting actually had its roots in the 1960s with the development of Generalized Markup Language (GML).虽然最常见的网页格式化语言是HTML,实际上文档格式的概念早在20世纪60年代随着通用置标语言(GML)的发展就形成了。9.2 HYPERTEXT430
  • 431. SGML. In 1986, the International Standards Organization adopted a variation of GML called Standard Generalized Markup Language, or SGML. The purpose of SGML was to help very large organizations format and categorize large collections of documents. The advantage of SGML is that it can run independent of any software program but, unfortunately, it is extremely complicated and difficult to learn. Probably for this reason, it has not been widely adopted.SGML(标准通用置标语言)。在1986年,国际标准组织正式通过了GML的一种变体叫做标准通用置标语言,或SGML。SGML的目标是帮助特大型组织对大量文档格式化并归类。SGML的优点是它能独立于任何软件程序运行,但不幸的是,它极端复杂和难学。或许因为这个理由,它没有被广泛地采用。9.2 HYPERTEXT431
  • 432. HTML. HTML (HyperText Markup Language) is a GML that is relatively easy to use. HTML provides Web page designers with a fixed set of markup “tags” that are used to format a Web page. When these tags are inserted into a Web page, they are read by the browser and interpreted into a page display. You can see the source HTML code for any Web page by simply clicking on the “Page Source” command found in all browsers.HTML(超文本链接标示语言)。HTML是相对容易使用的一种GML。HTML为网页设计者提供一组固定的标示“标签”用于格式化网页。当这些标签被插入一个网页之中时,他们被浏览器阅读并翻译为网页显示。你可以看见任何网页的HTML源代码,只需点击一下所有浏览器中都能找到的 "网页源文件"指令。9.2 HYPERTEXT432
  • 433. HTML functions to define the structure and style of a document, including the headings, graphic positioning, tables, and text formatting.5 Since its introduction, the two major browsers—Netscape’s Navigator and Microsoft’s Internet Explorer—have continuously added features to HTML to enable programmers to further refine their page layouts. Unfortunately, many of the enhancements only work in one company’s browser, and this development threatens the attainment of a universal computing platform. HTML的功能是定义文件的结构和风格,包括标题、图形定位、表格和本文格式。从HTML引入以来,两个主要的浏览器——Netscape(网景公司)的Navigator和Microsoft(微软公司)的Internet Explorer——不断地把特征加入HTML之中,使程序员能够进一步改进他们的页设计。不幸的是,许多功能的加强只有在一个公司的浏览器中起作用,而且这种发展威胁到通用计算机平台的实现。9.2 HYPERTEXT433
  • 434. HTML Web pages can be created with any text editor, such as Notepad or Wordpad, using Microsoft Word (simply save the Word document as a Web page) or any one of several Web page editors.HTML网页可以使用微软的Word或几种网页编辑器中任何一种通过本文编辑器生成,例如Notepad(记事本)或 Wordpad(写字本) (只需把Word文件保存为一个网页)。9.2 HYPERTEXT434
  • 435. XML. Extensible Markup Language (XML) takes Web document formatting a giant leap forward. XML is a new markup language specification developed by the W3C (the World Wide Web Consortium). XML is a markup language like HTML, but it has very different purposes. Whereas the purpose of HTML is to control the “look and feel” and display of data on the Web page, XML is designed to describe data and information.XML(可扩展标示语言)。XML使网络文件格式化发生了一次巨大的飞跃。XML是由万维网联合会开发的一种新型置标语言规范。XML是像HTML一样的一种置标语言,但是它又有非常不同的目的。XML是用于描述数据和信息,而HTML的目的是控制"表现与感觉" 并将数据在网页上显示。 9.2 HYPERTEXT435
  • 436. For instance, if you want to send a patient’s medical record—including diagnosis, personal identity, medical history information, and any doctor’s notes—from a database in Boston to a hospital in New York over the Web, it would be impossible using HTML. However, with XML, these rich documents (database records) for patients could be easily sent over the Web and displayed. 比如,如果你想要把一个病人的病历卡——包括诊断、个人身份、病史信息和任何医生笔记——通过网络从一个在波士顿的数据库发送到位于纽约的一所医院,使用HTML是不可能的。然而,使用XML,这些有关病人的富文件(数据库记录)可以容易通过网络发送并显示。 9.2 HYPERTEXT436
  • 437. XML is “extensible,” which means the tags used to describe and display data are defined by the user, whereas in HTML the tags are limited and predefined. XML can also transform information into new formats, such as by importing information from a database and displaying it as a table. With XML, information can be analyzed and displayed selectively, making it a more powerful alternative to HTML. This means that business firms, or entire industries, can describe all of their invoices, accounts payable, payroll records, and financial information using a Web-compatible markup language. Once described, these business documents can be stored on intranet Web servers and shared throughout the corporation.XML是 "可扩展的",意味着用于描述并显示数据的标签被使用者定义,而在HTML中标签是有限制的,而且是预先定义的。XML也能把信息转变成新的格式,例如从一个数据库输入信息并显示为一张表格。使用XML,数据能被有选择性地分析且显示,使它成为比HTML更有力的可选方案。这意味着商业公司,或整个行业,全部能使用与网络兼容的置标语言通过发票、可支付帐户、薪资记录和财政信息来描述。一旦完成描述,这些商业文件可以被储存在内联网网络服务器上并在整个公司共享。9.2 HYPERTEXT437
  • 438. XML is not yet a replacement for HTML. Currently, XML is fully supported only by Microsoft’s Internet Explorer 5, and is not supported by Netscape (although this may change). Whether XML eventually supplants HTML as the standard Web formatting specification depends a lot on whether it is supported by future Web browsers. Currently, XML and HTML work side by side on the same Web pages. HTML is used to define how information should be formatted, and XML is being used to describe the data itself.XML仍然不能替换HTML。当前,只有微软的Internet Explorer 5完全支持XML,而Netscape(网景公司)不支持 (虽然这种现象可能改变)。XML能否最终替代HTML作为标准的网络格式规范,在很大程度上仰赖于将来的网络浏览器是否支持它。目前,XML和HTML在相同的网页上并肩工作。HTML用来定义应该如何格式化信息,而XML用来描述数据它本身。9.2 HYPERTEXT438
  • 439. We have already described client/server computing and the revolution in computing architecture brought about by client/server computing. You already know that a server is a computer attached to a network that stores files, controls peripheral devices, interfaces with the outside world—including the Internet—and does some processing for other computers on the network.我们已经描述了客户机/服务器计算技术及其在计算机技术结构中引起的革命。你已经知道服务器是一台联接到网络的计算机,用于储存文件、控制外设、与外界——包括因特网接口,且为网络上的其他计算机进行一些处理。9.3 WEB SERVERS AND CLIENTS 439
  • 440. But what is a Web server? Web server software refers to the software that enables a computer to deliver Web pages written in HTML to client machines on a network that request this service by sending an HTTP request. The two leading brands of Web server software are Apache, which is free Web server shareware that accounts for about 60% of the market, and Microsoft’s NT Server software, which accounts for about 20% of the market.但什么是网络服务器?网络服务器软件是一种使计算机能够向网上客户机传递HTML网页的软件,而客户机通过发出HTTP请求申请这种服务。网络服务器软件的两种主要品牌是Apache和微软的NT服务器软件,前者是一种免费的网络服务器共享软件,约占有60%的市场;后者约占有20%的市场。9.3 WEB SERVERS AND CLIENTS 440
  • 441. Aside from responding to requests for Web pages, all Web servers provide some additional basic capabilities such as the following: File Transfer Protocol (FTP)—This protocol allows users to transfer files to and from the server. Some sites limit file uploads to the Web server, while others restrict downloads, depending on the user’s identity. 除了回应网页请求之外,所有的网络服务器还提供一些附加的基本能力,例如下列各项: 文件传输协议(FTP)——这个协议允许使用者从服务器来回移动文件。根据使用者的身份不同,一些网站限制文件上传到网络服务器,而其他网站限制下载。 9.3 WEB SERVERS AND CLIENTS 441
  • 442. Security services—These consist mainly of authentication services that verify that the person trying to access the site is authorized to do so. For Web sites that process payment transactions, the Web server also supports Secure Sockets Layer (SSL), the Internet protocol for transmitting and receiving information securely over the Internet. When private information such as names, phone numbers, addresses, and credit card data need to be provided to a Web site, the Web server uses SSL to ensure that the data passing back and forth from the browser to the server is not compromised.安全服务——主要由认证服务组成,确认人们试图对网站进行的访问是经过授权的。对于处理支付交易的网站,网络服务器也支持加密套接字协议层(SSL)——用于在因特网上安全地传输与接收信息的因特网协议。当私人信息如姓名、电话号码、地址和信用卡数据等需要向一个网站提供时,网络服务器使用SSL确保从浏览器到服务器来回传递的数据不被损害。9.3 WEB SERVERS AND CLIENTS 442
  • 443. Search engine—Just as search engine sites enable users to search the entire Web for particular documents, search engine modules within the basic Web server software package enable indexing of the site’s Web pages and content, and permit easy keyword searching of the site’s content. When conducting a search, a search engine makes use of an index, which is a list of all the documents on the server. The search term is compared to the index to identify likely matches.搜索引擎——正如搜索引擎网站使用户能够为特殊的文件搜寻整个万维网,基本网络服务器软件包中的搜寻引擎模块允许对网站的网页和内容进行索引,并允许网站内容的关键词搜索。当进行搜寻时,搜索引擎使用索引, 索引是服务器上所有文件的列表。将搜寻项与索引进行比较,确定可能的匹配 9.3 WEB SERVERS AND CLIENTS 443
  • 444. Data capture—Web servers are also helpful at monitoring site traffic, capturing information on who has visited a site, how long the user stayed there, the date and time of each visit, and which specific pages on the server were accessed. This information is compiled and saved in a log file, which can then be analyzed by a user log file. By analyzing a log file, a site manager can find out the total number of visitors, average length of each visit, and the most popular destinations, or Web pages.数据捕获——网络服务器还有助于监测网站访问量,捕获有关谁访问某个网站、用户在那里停留多久、每次访问的日期和时间、和服务器上哪个特定网页被存取等信息。这个信息被汇编并保存在一个日志文件中,然后能通过用户日志文件进行分析。通过分析一个日志文件,网站管理员能找出访客总数、平均访问时间长度和最流行的目的地或网页。9.3 WEB SERVERS AND CLIENTS 444
  • 445. The term Web server is sometimes also used to refer to the physical computer that runs Web server software. Leading manufacturers of Web server computers are IBM, Compaq, Dell, and Hewlett Packard. Although any personal computer can run Web server software, it is best to use a computer that has been optimized for this purpose. To be a Web server, a computer must have the Web server software described above installed and be connected to the Internet. Every Web server machine has an IP address. 术语网络服务器有时也被用于指运行网络服务器软件的实际计算机。网络服务器计算机的领先制造商是IBM(国际商用机器公司)、Compaq(康柏)、Dell(戴尔)和Hewlett Packard(惠普)。虽然任何个人计算机都能运行网络服务器软件,但是最好使用一部为这个目的最佳化的计算机。作为一个网络服务器,一部计算机必须安装上述网络服务器软件且联接到因特网。每部网络服务器计算机有一个IP地址。9.3 WEB SERVERS AND CLIENTS 445
  • 446. Aside from the generic Web server software packages, there are actually many types of specialized servers on the Web, from database servers that access specific information with a database, to ad servers that deliver targeted banner ads, to mail servers that provide mail messages, and video servers that provide video clips. At a small e-commerce site, all of these software packages might be running on a single machine, with a single processor. At a large corporate site, there may be hundreds of discrete machines, many with multiple processors, running specialized Web server functions described above.除了一般的网络服务器软件包之外,网络上其实还有许多类专用服务器, 从访问数据库特定信息的数据库服务器, 到递特定标题广告的广告服务器,到提供邮寄信息的邮件服务器,以及提供视频剪辑的视频服务器。在一个小型电子商务网站,所有的这些软件包可能在一部具有一个处理器的机器上运行。在一个大公司的网站,可能有数百台分布的机器, 多数具有多个处理器,运行上述特定的网络服务器功能 9.3 WEB SERVERS AND CLIENTS 446
  • 447. A Web client, on the other hand, is any computing device attached to the Internet that is capable of making HTTP requests and displaying HTML pages. The most common client is a Windows PC or Macintosh, with various flavors of UNIX machines a distant third. 另一方面,网络客户机是指任何一种联接到因特网、能够发出HTTP请求并显示网页的计算装置。最常见的客户机是采用Windows操作系统的个人计算机或麦金托什机,各种不同风格的UNIX机远远排在第三。9.3 WEB SERVERS AND CLIENTS 447
  • 448. The primary purpose of Web browsers is to display Web pages, but browsers also have added features, such as e-mail and newsgroups (an online discussion group or forum). 网络浏览器的主要目的是显示网页,但浏览器还有更多的功能, 例如电子邮件和新闻讨论组(在线讨论组或论坛)。 9.4 WEB BROWSERS 448
  • 449. Currently 94% of Web users use either Internet Explorer or Netscape Navigator, but recently some new browsers have been developed that are beginning to attract attention. The browser Opera is becoming very popular because of its speed—it is currently the world’s fastest browser—and because it is much smaller than existing browsers (it can almost fit on a single diskette). It can also remember the last Web page you visited, so the next time you surf, you can start where you left off. And like the big two, you can get it for free; the catch is that you have to watch blinking ads in one corner, or pay $40 for the ad-free version of Opera.目前,94%的网络用户使用Internet Explorer或Netscape Navigator浏览器,但是最近已开发出的一些新浏览器开始吸引人们的注意力。Oprea浏览器正在变得非常流行,因为它的速度——它是目前世界上最快的浏览器,而且因为它比现有浏览器小得多(它几乎可以装在一张软盘上)。它也能记得你访问过的最后一个网页,因此下回漫游时,你能从你停止的地方开始。而且像那两个大浏览器一样,你能免费得到它;其陷阱是你不得不看一个角落中可恶的广告,否则要支付40美元购买无广告版。9.4 WEB BROWSERS 449
  • 450. The browser NeoPlanet is also gaining new fans, primarily because of the 500+ skins, or design schemes, that come with it. Using skins, you can design the browser to look and sound just the way you’d like it to, rather than being limited to the standard look provided by Navigator and Internet Explorer. However, NeoPlanet requires Internet Explorer’s technology in order to operate, so you must also have IE installed on your computer.浏览器NeoPlanet也正在获得新的爱好者,主要因为它带有500多套界面或设计方案。使用不同界面,你能根据你喜欢看或听的方式设计浏览器,而不是被限于Netscape Navigator和Internet Explorer浏览器提供的标准外观。然而, NeoPlanet 需要Internet Explorer的技术来运行,因此你也必须在计算机上安装IE。9.4 WEB BROWSERS 450
  • 451. 学术论文的英文写作简介 一、科技论文的结构 Title(标题) Abstract(摘要) Keywords(关键词) Table of contents(目录) Nomenclature(术语表) Introduction(引言) Method(方法) Results(结果) Discussion(讨论) Conclusion(结论) Acknowledgement(致谢) Notes(注释) References(参考文献) Appendix(附录)正 文一篇完整规范的学术论文结构如右所示: 其中, Title, Abstract,Introduction,Method, Result,Discussion,Conclusion和Reference 八项内容是必不可少的,其他内容则根据具体需要而定 451
  • 452. 二、正文 学术论文的正文一般包括Method,Result,Discussion三个部分。这三部分主要描述研究课题的具体内容、方法,研究过程中所使用的设备、仪器、条件,并如实公布有关数据和研究结果等。Conclusion是对全文内容或有关研究课题进行的总体性讨论。它具有严密的科学性和客观性,反映一个研究课题的价值,同时提出以后的研究方向。 为了帮助说明论据、事实,正文中经常使用各种图表。最常用的是附图(Figure)和表(Table),此外还有图解或简图(Diagram)、曲线图或流程图(Graph)、视图(View)、剖面图(Profile)、图案(Pattern)等。在文中提到时,通常的表达法为: 如图 4 所示 As (is) shown in Fig.4, 如表 1 所示 As (is) shown in Tab.1,学术论文的英文写作简介 452
  • 453. 三、结论 在正文最后应有结论(Conclusions)或建议(Suggestions)。 (1) 关于结论可用如下表达方式: ① The following conclusions can be drawn from …(由……可得出如下结论) ② It can be concluded that …(可以得出结论……) ③ We may conclude that…或We come to the conclusion that…(我们得出如下结论……) ④ It is generally accepted (believed, held, acknowledged) that…(一般认为…)(用于表示肯定的结论) ⑤ We think (consider, believe, feel) that…(我们认为…)(用于表示留有商量余地的结论) (2) 关于建议可用如下表达方式。 ① It is advantageous to (do) ② It should be realized (emphasized, stressed, noted, pointed out ) that … ③ It is suggested (proposed, recommended, desirable) that … ④ It would be better (helpful, advisable) that… 学术论文的英文写作简介 453
  • 454. 四、结尾部分 1、致谢 为了对曾给予支持与帮助或关心的人表示感谢,在论文之后,作者通常对有关人员致以简短的谢词,可用如下方式: I am thankful to sb. for sth I am grateful to sb. for sth I am deeply indebted to sb. for sth I would like to thank sb. for sth. Thanks are due to sb. for sth The author wishes to express his sincere appreciation to sb. for sth. The author wishes to acknowledge sb. The author wishes to express his gratitude for sth.学术论文的英文写作简介 454
  • 455. 四、结尾部分 2、注释 注释有两种方式,一种为脚注,即将注释放在出现的当页底部;另一种是将全文注释集中在结尾部分。两种注释位置不同,方法一样。注释内容包括: (1) 引文出处。注释方式参见“参考文献”。 (2) 对引文的说明,如作者的见解、解释。 (3) 文中所提到的人的身份,依次为职称或职务、单位。如: Professor, Dean of Dept…. University(教授,……大学……系主任) Chairman, … Company, USA(美国……公司董事长) (4) 本论文是否曾发表过。学术论文的英文写作简介 455
  • 456. 四、结尾部分 3、参考文献 在论文的最后应将写论文所参考过的主要论著列出,目的是表示对别人成果的尊重或表示本论文的科学根据,同时也便于读者查阅。参考文献的列法如下: 如果是书籍,应依次写出作者、书名、出版社名称、出版年代、页数。如: Dailey, C.L. and Wood, F.C., Computation curves for compressible Fluid Problems, John Wiley & Sons, Inc. New York, 1949, pp.37-39 如果是论文,应依次写出作者、论文题目、杂志名称、卷次、期次、页数。如: Marrish Joseph G.,Turbulence Modeling for Computational Aerodynamics, AIAA J.Vol-21,No.7, 1983, PP.941-955 如果是会议的会刊或论文集,则应指出会议举行的时间、地点。如: Proceedings of the Sixth International Conference on Fracture Dec.4-10,1984, New Delhi, India 如果作者不止一人,可列出第一作者,其后加上et al。如:Wagner, R.S. et al, ….学术论文的英文写作简介 456
  • 457. Computer English Chapter 10 Computer and Network Security
  • 458. Key points: useful terms and definitions of computer security Difficult points: distinguish between four kinds of computer security breaches458
  • 459. Requirements:1. Principle of easiest penetration 2. The kinds of computer security breaches 3. What is firewall4. 了解科技论文标题的写法 459
  • 460. New Words & Expressions: breach 破坏,缺口 involve 包含,涉及,也可不译 depositor 寄托者 vulnerability 弱点,攻击 perimeter 周围,周边 penetrate vt. 攻破,攻击 Exposure 曝光,揭露 threat n. 威胁,恐吓 asset 资产 interruption 中断,打断 interception 截取 modification 修改 fabricate v. 伪造 tamper v. 篡改 spurious adj. 假的 10.1 Characteristics of Computer Intrusion and Kinds of Security Breaches Abbreviations: 460
  • 461. 10.1.1 入侵计算机的特点 Principle of Easiest Penetration. An intruder must be expected to use any available means of penetration. This will not necessarily be the most obvious means, nor will it necessarily be the one against which the most solid defense has been installed. 最容易攻破原理。入侵者必定要使用一种可以攻破的方法,这种方法既不可能是最常用的,也不可能是针对已经采取了最可靠的防范措施的方法。 This principle says that computer security specialists must consider all possible means of penetration, because strengthening one may just make another means more appealing to intruders. We now consider what these means of penetration are. 这一原理说明计算机安全专家必须考虑所有可能的攻击方法。由于你加强了某一方面,入侵者可能会想出另外的对付方法。我们现在就说明这些攻击的方法是什么。10.1 Characteristics of Computer Intrusion and Kinds of Security Breaches461
  • 462. 10.1 Characteristics of Computer Intrusion and Kinds of Security Breaches10.1.2 KINDS OF SECURITY BREACHES In security, an exposure is a form of possible loss or harm in a computing system; examples of exposures are unauthorized disclosure of data, modification of data, or denial of legitimate access to computing . A vulnerability is a weakness in the security system that might be exploited to cause loss or harm. 在计算机系统中,暴露是一种使安全完全丧失或受到伤害的一种形式;暴露的例子是非授权的数据公开、数据修改或拒绝合法的访问计算机。脆弱性是安全系统中的薄弱环节,它可能引起安全的丧失或伤害。462
  • 463. 10.1.2 KINDS OF SECURITY BREACHES A human who exploits a vulnerability perpetrates an attack on the system. Threats to computing systems are circumstances that have the potential to cause loss or harm; human attacks are examples of threats, as are natural disasters, inadvertent human errors, and internal hardware or software flaws. Finally, a control is a protective measure-an action, a device, a procedure, or a technique-that reduces a vulnerability. 人可利用脆弱性对系统进行罪恶的攻击。对计算机系统的威胁是引起安全丧失或伤害的环境;人们的攻击是威胁的例子,如自然灾害,人们非故意错误和硬件或软件缺陷等。最后,控制是一种保护性措施——控制可以是一种动作,一个设备,一个过程或一种技术——减少了脆弱性。 10.1 Characteristics of Computer Intrusion and Kinds of Security Breaches463
  • 464. 10.1.2 KINDS OF SECURITY BREACHES The major assets of computing systems are hardware, software, and data. There are four kinds of threats to the security of a computing system: interruption, interception, modification, and fabrication. The four threats all exploit vulnerabilities of the assets in computing systems. These four threats are shown in Fig.10-1. 计算机系统的主要资源是硬件、软件和数据。有四种对计算机安全的威胁:中断,截取,篡改和伪造。这四种威胁都利用了计算机系统资源的脆弱性,图10-1表示这四种威胁。10.1 Characteristics of Computer Intrusion and Kinds of Security Breaches464
  • 465. Fig.10-1 Four classes of System Security Failures465
  • 466. 10.1.2 KINDS OF SECURITY BREACHES In an interruption, an asset of the system becomes lost or unavailable or unusable. An example is malicious destruction of a hardware device, erasure of a program or data file, or failure of an operating system file manager so that it cannot find a particular disk file. (1)在中断情况下,系统资源开始丢失,不可用或不能用。例如,蓄意破坏硬件设备,抹除程序或数据文件或造成操作系统的文件管理程序故障,以致不能找到某一磁盘文件。10.1 Characteristics of Computer Intrusion and Kinds of Security Breaches466
  • 467. 10.1.2 KINDS OF SECURITY BREACHES (2) An interception means that some unauthorized party has gained access to an asset. The outside party can be a person, a program, or a computing system. Examples of this type of failure are illicit copying of program or data files, or wiretapping to obtain data in a network. While a loss may be discovered fairly quickly, a silent interceptor may leave no traces by which the interception can be readily detected. (2)截取是指某一非特许用户掌握了访问资源的权利。外界用户可以是一个人、一个程序或一个计算机系统。这种威胁的例子如程序或数据文件的非法拷贝,或私自接线入网去获取数据。数据丢失可能会很快被发现,但很可能截取者并不留下任何容易检测的痕迹。 10.1 Characteristics of Computer Intrusion and Kinds of Security Breaches467
  • 468. 10.1.2 KINDS OF SECURITY BREACHES (3) If an unauthorized party not only accesses but tampers with an asset, the failure becomes a modification. For example, someone might modify the values in a database, alter a program so that it performs an additional computation, or modify data being transmitted electronically. It is even possible for hardware to be modified. Some cases of modification can be detected with simple measures, while other more subtle changes may be almost impossible to detect . (3)如果非授权用户不仅可以访问计算机资源,而且可以篡改资源,则威胁就成为修改了。例如,某人可以修改数据库中的值, 更换一个程序,以便完成另外的计算,或修改正在传送的数据, 甚至还 可能修改硬件。某些情况下可以用简单的测量手段检测 出所做的修改,但某些微妙的修改是不可能检测出来的。 10.1 Characteristics of Computer Intrusion and Kinds of Security Breaches468
  • 469. 10.1.2 KINDS OF SECURITY BREACHES (4) Finally, an unauthorized party might fabricate counterfeit objects for a computing system. The intruder may wish to add spurious transactions to a network communication system. or add records to an existing data base . Sometimes these additions can be detected as forgeries, but if skillfully done, they are virtually indistinguishable from the real thing. (4)最后,非授权用户可以伪造计算机系统的一些对象。入侵者妄图向网络通信系统加入一个假的事务处理业务,或向现有的数据库加入记录。有时,这些增加的数据可以作为伪造品检测出来,但如果做得很巧妙,这些数据实际上无法与真正的数据分开。10.1 Characteristics of Computer Intrusion and Kinds of Security Breaches469
  • 470. 10.1 Characteristics of Computer Intrusion and Kinds of Security Breaches10.1.2 KINDS OF SECURITY BREACHES These four classes of interference with computer activity-interruption, interception, modification, and fabrication-can describe the kinds of exposures possible[2]. 这四种对计算机工作的干扰——中断,截取,修改或伪造——表明了可能出现的几种威胁类型。 470
  • 471. New Words & Expressions: cryptography n. 密码学 encryption 加密 cipher n. 密码(钥),加密程序 decrypt v. 解密 transit 通行(过),运输 plaintext n. 明文 cyphertext n. 密文 scheme n. 计划,方案 secret-key 秘钥 public-key 公钥 symmetric adj. 对称的 data integrity 数据完整性 session key 会话密钥 crack v. 解开,裂开 hacker 黑客,计算机窃贼 encode v. 编码 triple-encryption 三重加密 built-in 内在(固有)的, state-of-the-art 最新的 proliferate v. 增生,扩散 10.2 Modern Cryptography- Data EncryptionAbbreviations : DES (Data Encryption System) 数据加密系统 DCE ( Distributed Computing Environment) 分布式计算环境471
  • 472. 10.2 Modern Cryptography- Data EncryptionIf the receiver of the encrypted data wants to read the original data, the receiver must convert it back to the original through a process called decryption. Decryption is the inverse of the encryption process. In order to perform the decryption, the receiver must be in possession of a special piece of data called the key. 如果接收到加密数据的人要看原来的数据,就必须把数据转换为原来的形式,这个过程称为解密。解密是加密过程的逆过程。为了进行解密,接收者必须有称为密钥的特殊数据。 The two main competing cryptography schemes are known as the secret-key (symmetric) system and the public-key (asymmetric) system. The secret-key system uses a single, wholly secret sequence both to encrypt and to decrypt messages. The public-key system uses a pair of mathematically related sequences, one each for encryption and decryption [1]. 现在有两种主要的、相互竞争的密码术:秘钥(对称)和公钥(不对称)系统。秘钥系统采用单一的绝密序列,对报文进行加密和解密。公钥系统采用一对数学上相关的序列,一个用于加密,另一个用于解密。472
  • 473. 10.2 Modern Cryptography- Data EncryptionSecret-key encryption One of the most popular secret-key encryption schemes is IBM’s Data Encryption System (DES), which became the U.S. federal standard in 1997. the standard form uses a 56-bit key to encrypt 64-bit data blocks. The following is a notation for relating plaintext, ciphertext, and keys. We will use C=E k (P) to mean that the encryption of the plaintext P using key k gives the ciphertext C. similarly, P=D k (C) represents of decryption of C to get the plaintext again. It then follows that D k ( E k (P))=P 密钥加密 IBM的数据加密系统(DES)是最流行的密钥加密方案之一。1977年,该方案成为美国联邦标准。该标准形式采用56位的密钥对64位的数据块进行加密。 下面是有关明文、密文和密钥关系的表示法。我们用C=E k (P)表示用密钥K对明文P加密,得到密文C。类似的,P=D k (C)代表对C解密得到明文。因而遵循:D k (E k (P))=P473
  • 474. 10.2 Modern Cryptography- Data EncryptionDES has been studied by many of the world’s leading cryptographers, but no weaknesses have been uncovered. To crack a DES-encrypted message a hacker or commercial spy would need to try 255 possible keys. This type of search would need days of computer time on the world’s fastest supercomputers. Even then, the message may not be cracked if the plaintext is not easily understood [2]. 为了打开一个DES加密的报文,黑客或商业间谍需要试验255种可能的密钥,这种搜索在世界上最快的巨型机上也需好几天的计算机时间。如果未加密的“明文”是不易理解的,即使算出报文也可能解不开。474
  • 475. 10.2 Modern Cryptography- Data EncryptionDevelopers using DES can improve security by changing the keys frequently, using temporary session keys, or using triple-encryption DES. With triple DES, each 64-bit block is encrypted under three different DES keys. Recent research has confirmed that triple-DES is indeed more secure than single-DES. The User Data Masking Encryption Facility is an export-grade algorithm substituted for DES in several IBM products, such as the Distributed Computing Environment (DCE) [3]. 使用DES的开发人员可以通过频繁更改密钥,使用临时的会话密钥或使用三重加密DES来提高安全性。使用三重DES时,每个64位数据块用三种不同的DES密钥加密。最新研究已确认三重DES确实比单重DES更安全。475
  • 476. 10.2 Modern Cryptography- Data EncryptionPublic-key encryption The key distribution problem has always been the weak link in the secret-key systems. Since the encryption key and decryption key are the same( or easily derived from one another) and the key has to be distributed to all users of the system, it seemd as if there was an inherent built-in problem: keys had to be protected from theft, but they also had to be distributed, so they could not just be locked up in a bank vault. 公钥加密 密钥的分布问题在秘钥系统中一直是一个薄弱环节。因为加密密钥和解密密钥是相同的(或彼此容易推出来)并且这个密钥必须分配给该秘钥系统的所有用户,这好像是存在一个固有的内部问题,必须保护密钥不被偷窃,但又必须分布出去,所以它们不可能只是锁在银行的地下室里。476
  • 477. 10.2 Modern Cryptography- Data EncryptionEncryption can be used to protect data in transit as well as data in storage. Some vendors provide hardware encryption devices that can be used to encrypt and decrypt data. There are also software encryption packages which are available either commercially or as free software. 加密可以用来保护传输中的数据和存储器中的数据。一些厂家提供硬件加密设备,用来加密和解密数据。也可买到软件加密程序包或作为自由软件免费获得。 Encryption can be defined as the process of tasking information that exists in some readable form (plaintext) and converting it into a form (ciphertext) so that it cannot be understood by others. 加密可以定义为把现有的、以某种可读形式(明文)的信息转换成其他人不能理解的形式(密文)的过程。477
  • 478. 10.2 Modern Cryptography- Data EncryptionIn public key cryptosystem, the encryption and decryption keys were different, and plaintext encrypted with the public key can only be deciphered with the private key from the same pair. Conversely, plaintext encrypted with the private key can be decrypted only with the public key[4] ( it is used in electronic signatures). The notations for these are as follows. C=E k (P) , P=D k1(C)=D k1 (E k (P)) or C=D k1 (P), P=E k (C)=E k (D k1 (P)) 在公钥秘钥系统中,加密和解密密钥是不同的。并且用公开密钥加密的明文只能用同一对密钥中的秘密密钥解密。相反,用私有密钥加密的明文只能用公开密钥解密(它用于电子签名)。这些关系的表示法如下:(见上式) Here k is a public key and k1 is private key( or secret key). Users can make their public keys freely available or place them at a key distribution center for others to access. However, the private key must be kept safe. In public-key systems there is no need to find a safe channel for communicating a shared secret key. 这里K是公开密钥,K1是私有密钥(或秘密密钥)。用户可以让他们的公开密钥自由地使用,或把它们放在密钥分配中心供其他人存取。然而,私有密钥必须安全的保存。在公开密钥系统,无需找一条传送共享的私有密钥的安全通道。478
  • 479. 10.3 How Firewalls WorkNew Words & Expressions firewall n. 防火墙 offensive adj. 无理的,攻击性的 hacker n. 黑客 filter v. 过滤,滤过,渗入 private 私有的,秘密地 packet n. 小包,信息包 employee n. 职员,雇工 telnet n. 远程登录 traffic n. 流量 proxy n. 代理 retrieve v, 检索 match n.比较,匹配,符合 customizable 可定制的 block n. 妨碍,阻碍 port n. 端口 bug n. 故障,(程序)错误 unsolicited adj.主动提供的 junk n.垃圾,无用数据 spam n. 垃圾邮件 counter v. 还击,驳回 session n. 会话 inundate v. 淹没 macro [计]宏指令,宏功能 viruse n. 病毒479
  • 480. 10.3 How Firewalls WorkAbbreviations HTTP (Hypertext Transfer Protocol) 超文本传输协议 FTP (File Transfer Protocol) 文件传输协议 SMTP (Simple Mail Transfer Protocol) 简单邮件传送协议 ICMP (Internet Control Message Protocol) 网际控制报文协议 A small home network has many of the same security issues that a large corporate network does. You can use a firewall to protect your home network and family from offensive Web sites and potential hackers. 一个小型家庭网有着与大公司的网络相同的安全问题。防火墙可以保护你的家庭网和家庭免遭恶意网站和潜在黑客的攻击。 480
  • 481. 10.3 How Firewalls Work Basically, a firewall is a barrier to keep destructive forces away from your property. In fact, that’s why it’s called a firewall. Its job is similar to a physical firewall that keeps a fire from spreading from one area to the next. 实质上,防火墙就是一个屏障,保护私有财产不受破坏。事实上,这就是它被称为防火墙的原因。它的作用类似于一堵防止火灾从一处蔓延到另一处的实实在在的防火墙。 What it does A firewall is simply a program or hardware device that filters the information coming through the Internet connection into your private network or computer system. If an incoming packet of information is flagged by the filters, it is not allowed through. 防火墙做什么 一个防火墙就是一个程序或者一台硬件设备,用于过滤通过Internet连接进入你的专用网或计算机系统中的信息。如果一个输入的信息包被过滤器做了标记,它就不允许通过。 481
  • 482. 10.3 How Firewalls WorkFirewalls use one or more of three methods to control traffic flowing in and out of the network: (1) Packet filtering: Packets (small chunks of data) are analyzed against a set of filters. Packets that make it through the filters are sent to the requesting system and all others are discarded. (2) Proxy service: Information from the Internet is retrieved by the firewall and then sent to the requesting system and vice versa. 防火墙使用下列三种方法之一或几种来控制进出网络的通信: (1)数据包过滤:数据包(小块数据)由一组过滤器进行分析。能通过过滤器的数据包被发送到发出请求的系统,其它的被丢弃。 (2)代理服务:来自Internet的信息通过防火墙进行检索,然后发送到提出请求的系统,反之亦然。482
  • 483. (3) Stateful inspection: A newer method that doesn’t examine the contents of each packet but instead compares certain key parts of the packet to a database of trusted information. Information traveling from inside the firewall to the outside is monitored for specific defining characteristics, then incoming information is compared to these characteristics. If the comparison yields a reasonable match, the information is allowed through. Otherwise it is discarded. (3)状态检查:一种更新的方法,并不检查每个数据包的内容,而是将数据包的某个关键部分与一个可信的信息数据库比较。从防火墙内部传输到外部的信息可根据特别规定的特性进行监控,然后将输入信息与这些特性相比较,若生成一个合理的匹配,则信息允许通过,否则就丢弃。10.3 How Firewalls Work483
  • 484. The level of security you establish will determine how many of these threats can be stopped by your firewall. The highest level of security would be to simply block everything. Obviously that defeats the purpose of having an Internet connection. But a common rule of thumb[3 is to block everything, then begin to select what types of traffic you will allow. You can also restrict traffic that travels through the firewall so that only certain types of information, such as e-mail, can get through. For most of us, it is probably better to work with the defaults provides by the firewall developer unless there is a specific reason to change it. 你所设定的安全级别将决定这些威胁有多少能够被你的防火墙所阻止。最高安全级别就是阻断一切。很显然,这就失去了进行Internet连接的意义。但通常的经验做法是阻断一切,然后,开始选择你将允许什么类型的通信。你还可以限制通过防火墙的通信,以便只有几种信息通过,如电子邮件。对我们大多数人来说,除非有特殊的理由要改变它,否则最好在防火墙开发商提供的默认条件下工作。10.3 How Firewalls Work484
  • 485. One of the best things about a firewall from a security standpoint is that it stops anyone on the outside from logging onto a computer in your private network. While this is a big deal[4] for businesses, most home networks will probably not be threatened in this manner. 从安全的角度来看,防火墙的一个优点就是它能阻止任何外来人登录到专用网中的一台计算机上,这对企业很重要,大多数家庭网在这种方式下可以不受威胁。10.3 How Firewalls Work485
  • 486. 学术文章的标题主要有三种结构:名词性词组(包括动名词),介词词组,名词词组+介词词组。间或也用一个疑问句作标题(多用在人文社会科学领域),但一般不用陈述句或动词词组作标题。 一、名词性词组 名词性词组由名词及其修饰语构成。名词的修饰语可以是形容词、介词短语,有时也可以是另一个名词。名词修饰名词时,往往可以缩短标题的长度。以下各标题分别由两个名词词组构成。例如: Latent demand and the browsing shopper (名词词组+名词词组) Cost and productivity (名词+名词)科技论文标题的写法 486
  • 487. 科技论文标题的写法二、介词词组 介词词组由介词十名词或名词词组构成。如果整个标题就是一个介词词组的话,一般这个介词是“on”,意思是“对……的研究”。例如: From Knowledge Engineering to Knowledge Management (介词词组+介词词组) On the correlation between working memory capacity and performance on intelligence tests487
  • 488. 科技论文标题的写法三、名词/名词词组+介词词组 这是标题中用得最多的结构。例如: Simulation of Controlled Financial Statements (名词+介词词组) The impact of internal marketing activities on external marketing outcomes (名词+介词词组+介词词组) Diversity in the Future Work Force (名词+介词词组) Models of Sustaining Human and Natural Development (名词+介词词组) 标题中的介词词组一般用来修饰名词或名词词组,从而限定某研究课题的范围。这种结构与中文的“的”字结构相似,区别是中文标题中修饰语在前,中心词在后。英文正好相反,名词在前,而作为修饰语的介词短语在后。例如: Progress on Fuel Cell and its Materials (燃料电池及其材料进展) 488
  • 489. 科技论文标题的写法四、其他形式 对于值得争议的问题,偶尔可用疑问句作为论文的标题,以点明整个论文讨论的焦点。例如: Is B2B e-commerce ready for prime time? Can ERP Meet Your eBusiness Needs?489
  • 490. 科技论文标题的写法有的标题由两部分组成,用冒号(:)隔开。一般来说,冒号前面一部分是研究的对象、内容或课题,比较笼统,冒号后面具体说明研究重点或研究方法。这种结构可再分为三种模式。 模式1 研究课题:具体内容。例如: Microelectronic Assembly and Packaging Technology:Barriers and Needs The Computer Dictionary Project: an update 模式2 研究课题:方法/性质。例如: B2B E-Commerce: A Quick Introduction The Use of Technology in Higher Education Programs: a National Survey 模式 3 研究课题:问题焦点。例如: Caring about connections: gender and computing 490
  • 491. Computer English Chapter 11 Database Management
  • 492. Key points: useful terms and definitions of Database Management Difficult points: Classification of the logical structuring techniques of DBMS492
  • 493. Requirements:1. Principle of easiest penetration 2. The kinds of computer security breaches 3. What is firewall4. 了解英文摘要的写作技巧493
  • 494. New Words & Expressions: facilitate 使容易,促进 retrieval n. 检索 field n. 字段, record 记录, alphabetically 按字母顺序地 chronologically 按年代顺序排 break down v. 分解 build up 建造,装配,组成 encyclopedia n. 百科全书 reference n. 涉及,参考,引用 bibliography 书目,参考书目 periodical n. 期刊,杂志 literature n. 文献,著作 professional n. 专业人员,专家11.1 Overview Abbreviations: 494
  • 495. A database consists of a file or a set of files. The information in these files may be broken down into records, each of which consists of one or more fields. Fields are the basic units of data storage, and each field typically contains information pertaining to one aspect or attribute of the entity described by the database. Using keywords and various sorting commands, users can rapidly search, rearrange, group, and select the fields in many records to retrieve or create reports on particular aggregates of data. 一个数据库由一个文件或文件集合组成。这些文件中的信息可分解成一个个记录,每个记录有一个或多个域。域是数据存储的基本单位,每个域一般含有由数据库描述的属于实体的一个方面或一个特性的信息。用户使用键盘和各种排序命令,能够快速查找、重排、分组并在查找的许多记录中选择相应的域,建立特定集上的报表。11.1 Overview495
  • 496. 11.1 OverviewDatabase records and files must be organized to allow retrieval of the information. Early systems were arranged sequentially (i.e., alphabetically, numerically, or chronologically); the development of direct-access storage devices made possible random access to data via indexes. Queries are the main way users retrieve database information. Typically, the user provides a string of characters, and the computer searches the database for a corresponding sequence and provides the source materials in which those characters appear. A user can request, for example, all records in which the content of the field for a person’s last name is the word Smith. 数据库记录和文件的组织必须确保能对信息进行检索。早期的系统是顺序组织的(如:字母顺序、数字顺序或时间顺序);直接访问存储设备的研制成功使得通过索引随机访问数据成为可能。用户检索数据库信息的主要方法是query(查询)。通常情况下,用户提供一个字符串,计算机在数据库中寻找相应的字符序列,并且给出字符串在何处出现。比如,用户能够在所有记录中寻找所有last name域为Smith的记录。496
  • 497. In flat databases [2], records are organized according to a simple list of entities; many simple databases for personal computers are flat in structure. The records in hierarchical databases are organized in a treelike structure, with each level of records branching off into a set of smaller categories. Unlike hierarchical databases, which provide single links between sets of records at different levels, network databases create multiple linkages between sets by placing links, or pointers, to one set of records in another; the speed and versatility of network databases have led to their wide use in business. 在非结构化的数据库中,按照实体的一个简单列表组织记录;很多个人计算机的简易数据库是非结构的。层次型数据库按树型组织记录,每一层的记录分解成更小的属性集。层次型数据库在不同层的记录集之间提供一个单一链接,与此不同,网络型数据库在不同记录集之间提供多个链接,这是通过设置指向其它记录集的链或指针来实现的。网络型数据库的速度及多样性使其在企业中得到广泛应用。11.1 Overview497
  • 498. Relational databases are used where associations among files or records cannot be expressed by links; a simple flat list becomes one table, or “relation”, and multiple relations can be mathematically associated to yield desired information. Object-oriented databases store and manipulate more complex data structures, called “objects”, which are organized into hierarchical classes that may inherit properties from classes higher in the chain; this database structure is the most flexible and adaptable. 当文件或记录间的关系不能用链表达时,使用关系型数据库。一个表或一个“关系”,就是一个简单的非结构列表。多个关系可通过数学关系提供所需信息。面向对象的数据库存储并处理更复杂的称为对象的数据结构,可组织成有层次的类,其中的每个类可以继承层次链中更高一级类的特性,这种数据库结构最灵活,最具适应性。11.1 Overview498
  • 499. New Words & Expressions: sequential 顺序的,连续的 integrate 综合,使成整体 access v. 访问 retrieve v.找回,检索 employ v.使用 list structure n.链表结构 invoice n. 发票 pointer n.指针 hierarchical structure 树结构 subordinate adj. 从属的 network structure 网状结构 relational structure 关系结构 physical structure 物理结构11.2 DBMS STRUCTURING TECHNIQUES Abbreviations : DBMS(Database Management System) 数据库管理信息系统499
  • 500. 11.2 DBMS STRUCTURING TECHNIQUES DBMS is able to access and retrieve data from nonkey record fields. That is, the DBMS is able to structure and tie together the logically related data from several large files. DBMS可综合几个文件的数据项以回答用户对信息的查询,这就意味着DBMS能够访问和检索非关键记录字段的数据,即DBMS能够将几个大文件中逻辑相关的数据组织并连接在一起。 Logical Structures. Identifying these logical relationships is a job of the data administrator. A data definition language is used for this purpose. The DBMS may then employ one of the following logical structuring techniques during storage access, and retrieval operations [1]: 逻辑结构。确定这些逻辑关系是数据管理者的任务,由数据定义语言完成。DBMS在存储、访问和检索操作过程中可选用以下逻辑构造技术: 500
  • 501. 11.2 DBMS STRUCTURING TECHNIQUES 1. List structures. In this logical approach, records are linked together by the use of pointers. A pointer is a data item in one record that identifies the storage location of another logically related record. Records in a customer master file, for example, will contain the name and address of each customer, and each record in this file is identified by an account number. During an accounting period, a customer may buy a number of items on different days. Thus, the company may maintain an invoice file to reflect these transactions. 链表结构。在该逻辑方式中,记录通过指针链接在一起。指针是记录中的一个数据项,它指出另一个逻辑相关的记录的存储位置,例如,顾客主文件中的记录将包含每个顾客的姓名和地址,而且该文件中的每个记录都由一个账号标识。在记账期间,顾客可在不同时间购买许多东西,公司保存一个发票文件以反映这些交易。501
  • 502. 11.2 DBMS STRUCTURING TECHNIQUES A list structure could be used in this situation to show the unpaid invoices at any given time. Each record in the customer file would contain a field that would point to the record location of the first invoice for that customer in the invoice file (fig11-1). This invoice record, in turn, would be linked to later invoices for the customer. The last invoice in the chain would be identified by the use of a special character as a pointer. 这种情况下可使用链表结构,以显示给定时间内未支付的发票。顾客文件中的每个记录都包含这样一个字段,该字段指向发票文件(图11-1)中该顾客的第一个发票的记录位置,该发票记录又依次与该顾客的下一个发票记录相连,此链接的最后一个发票记录由一个作为指针的特殊字符标识。502
  • 503. PointerInvoice number Invoice number PointerInvoice number Invoice number Invoice number Invoice number Fig 11-1 List Structure503
  • 504. 11.2 DBMS STRUCTURING TECHNIQUES Hierarchical (tree) structures. In this logical approach, data units are structured in multiple levels that graphically resemble an "upside down" tree with the root at the top and the branches formed below. There's a superior-subordinate relationship in a hierarchical (tree) structure. Below the single-root data component are subordinate elements or nodes, each of which, in turn, "own" one or more other elements (or none) [3]. Each element or branch in this structure below the root has only a single owner. Thus, as we see in fig11-2, a customer owns an invoice, and the invoice has subordinate items. The branches in a tree structure are not connected. 层次(树型)结构。该逻辑方式中,数据单元的多级结构类似一棵“倒立”的树,该树的树根在顶部,而树枝向下延伸。在层次(树型)结构中存在主-从关系,唯一的根数据下是从属的元或节点,而每个从属的元或节点又依次“拥有”一个或多个其它元(或者没有) 。该结构中根下面的每个元或树枝都只有一个所有者,这样,正如我们在图11-2中所看到的,一个customer(顾客)拥有一个invoice(发票),而invoice(发票)又有从属项。在树型结构中,树枝不能相连。504
  • 505. 11.2 DBMS STRUCTURING TECHNIQUES Network Structures. Unlike the tree approach, which does not permit the connection of branches, the network structure permits the connection of the nodes in a multidirectional manner (see fig11-3). Thus, each node may have several owners and may, in turn, own any number of other data units. Data management software permits the extraction of the needed information from such a structure by beginning with any record in a file. 网状结构。网状结构不像树型结构那样不允许树枝相连,它允许节点间多个方向连接(见图12-4),这样,每个节点都可能有几个所有者,而它又可能拥有任意多个其它数据单元。数据管理软件允许从文件的任一记录开始提取该结构中的所需信息。 505
  • 506. 11.3 Oracle的数据库管理功能 New Words & Expressions add-on adj. 附加的 repository v.综合,使成整体 console n. 控制台 optional adj. 可选择的,随意的 monitor n. 监控,监视 load n. 负载,加载 tuning n. 调谐,调整 tracking n. 跟踪 bottleneck n. 瓶颈 proactive adj.前摄的 eliminate v. 排除,消除 upgrade v. 使升级,提升 initiate v. 开始,初始化 wizard n. 向导,范例 mundane a. 平凡 (世俗)的 critical adj. 临界的,关键性的 archivelog n.. 档案日志 utility n. 实用程序,效用 expire v 期满,到期 incremental adj. 增加的 bundle v. 捆绑,扎 facility n. 设备,工具506
  • 507. 11.3 Oracle的数据库管理功能 Oracle includes many features that make the database easier to manage. We’ve divided the discussion in this section into three categories: Oracle Enterprise Manager, add-on packs, backup and recovery. Oracle Enterprise Manager As part of every Database Server, Oracle provides the Oracle Enterprise Manager (EM), a database management tool framework with a graphical interface used to manage database users, instances, and features (such as replication) that can provide additional information about the Oracle environment. Oracle包括许多使数据库易于管理的功能,分三部分讨论:Oracle企业管理者、附加包、备份和恢复。 Oracle企业管理者 Oracle数据库服务器包括以下部分:Oracle企业管理者(EM)、一个带有图形接口的用于管理数据库用户、实例和提供Oracle环境等附加信息功能 (如:复制) 的数据库管理工具框架。507
  • 508. 英文摘要(Abstract)的写作应用很广。论文摘要是全文的精华,是对一项科学研究工作的总结,对研究目的、方法和研究结果的概括。 一、摘要的种类与特点 摘要主要有以下四种。 第一种是随同论文一起在学术刊物上发表的摘要。这种摘要置于主体部分之前,目的是让读者首先了解一下论文的内容,以便决定是否阅读全文。一般来说,这种摘要在全文完成之后写。字数限制在100~150字之间。内容包括研究目的、研究方法、研究结果和主要结论。 第二种是学术会议论文摘要。会议论文摘要往往在会议召开之前几个月撰写,目的是交给会议论文评审委员会评阅,从而决定是否能够录用。所以,比第一种略为详细,长度在200—300字之间。会议论文摘要的开头有必要简单介绍一下研究课题的意义、目的、宗旨等。如果在写摘要时,研究工作尚未完成,全部研究结果还未得到,那么,应在方法、目的、宗旨、假设等方面多花笔墨。英文摘要的写作技巧 508
  • 509. 英文摘要的写作技巧第三种为学位论文摘要。学士、硕士和博士论文摘要一般都要求用中、英文两种语言写。学位论文摘要一般在400字左右,根据需要可以分为几个段落。内容一般包括研究背景、意义、主旨和目的;基本理论依据,基本假设;研究方法;研究结果;主要创新点;简短讨论。不同级别的学位论文摘要,要突出不同程度的创新之处,指出有何新的观点、见解或解决问题的新方法。 第四种是脱离原文而独立发表的摘要。这种摘要更应该具有独立性、自含性、完整性。读者无需阅读全文,便可以了解全文的主要内容。509
  • 510. 英文摘要的写作技巧二、摘要的内容与结构 摘要内容一般包括: Ø         目的(objectives,purposes):包括研究背景、范围、内容、要解决的问题及解决这一问题的重要性和意义。 Ø         方法(methods and materials):包括材料、手段和过程。 Ø         结果与简短讨论(results and discussions):包括数据与分析。 Ø         结论(conclusions):主要结论,研究的价值和意义等。 概括地说,摘要必须回答“研究什么”、“怎么研究”、“得到了什么结果”、“结果说明了什么”等问题。 无论哪种摘要,语言特点和文体风格也都相同。首先必须符合格式规范。第二,语言必须规范通顺,准确得体,用词要确切、恰如其分,而且要避免非通用的符号、缩略语、生偏词。另外,摘要的语气要客观,不要做出言过其实的结论。510
  • 511. 英文摘要的写作技巧三、学术期刊论文摘要 1、摘要的目的 摘要是论文的梗概,提供论文的实质性内容的知识。摘要的目的在于:给读者关于文献内容的足够的信息,使读者决定是否要获得论文。 2、摘要的要素 1)       目的——研究、研制、调查等的前提、目的和任务,所涉及的主题范围。 2)       方法——所用的原理、理论、条件、对象、材料、工艺、结构、手段、装备、程序等。 3)       结果——实验的、研究的结果、数据,被确定的关系,观察结果,得到的效果、性能等。 4)      结论——结果的分析、研究、比较、评价、应用,提出的问题等。 3、摘要的篇幅 摘要的篇幅取决于论文的类型。但无论哪一种论文,都不能超过150 words。 511
  • 512. 英文摘要的写作技巧4、摘要的英文写作风格(公认的英文摘要写作规范) 1)         句子完整、清晰、简洁。 2)         用简单句。为避免单调,改变句子的长度和句子的结构。 3)         用过去时态描述作者的工作,因它是过去所做的。但是,用现在时态描述所做的结论。 4)         避免使用动词的名词形式。如: 正:“Thickness of plastic sheet was measured” 误:“measurement of thickness of plastic sheet was made” 5)         正确地使用冠词,既应避免多加冠词,也应避免蹩脚地省略冠词。如: 正:“Pressure is a function of the temperature” 误:“The pressure is a function of the temperature”; 512
  • 513. 英文摘要的写作技巧4、摘要的英文写作风格 6)         使用长的、连串的形容词、名词、或形容词加名词来修饰名词。为打破这种状态,可使用介词短语,或用连字符连接名词词组中的名词,形成修饰单元。例如: 应写为“The chlorine-containing propylene-based polymer of high melt index”, 而不写为“The chlorine containing high melt index-propylene based polymer” 7)         使用短的、简单的、具体的、熟悉的词。不使用华丽的词藻。 8)         使用主动语态而不使用被动语态。“A exceeds B”读起来要好于“B is exceeded by A”。使用主动语态还有助于避免过多地使用类似于“is”, “was”, “are”和“were”这样的弱动词。513
  • 514. 英文摘要的写作技巧4、摘要的英文写作风格 9)         构成句子时,动词应靠近主语。避免形如以下的句子: “The decolorization in solutions of the pigment in dioxane, which were exposed to 10 hr of UV irradiation, was no longer irreversible.” 改进的句子,应当是: “When the pigment was dissolved in dioxane, decolorization was irreversible, after 10 hr of UV irradiation.” 10)      避免使用那些既不说明问题,又没有任何含意的短语。例如: “specially designed or formulated”,“ The author discusses”, “The author studied” 应删去。 不使用俚语、非英语的句子,慎用行话和口语,不使用电报体。 514
  • 515. Computer English Chapter 12 Multimedia
  • 516. Key points: useful terms and definitions of Multimedia Difficult points: Applications of multimedia516
  • 517. Requirements:Multimedia Equipments 2. What is multimedia?3. Main elements of multimedia4. 了解英文摘要的写作技巧517
  • 518. New Words & Expressions: Audio sound n.声音 retention n. 保留,保持 Static Graphics Images 静态图像 aid v. 援助,帮助 animation n. 动画 full-motion video 全运动影像12.1 Multimedia Abbreviations: MIDI (Musical Instrument Digital Interface) 乐器数字接口 518
  • 519. Multimedia Equipment Multimedia requires sound and graphics capability. A speedy processor chip plus a CD-ROM drive or DVD drive are also desirable. Today, multimedia components are standard equipment even on many inexpensive computers. 多媒体设备 多媒体需要声音和图形功能。还需要一个快速的处理器芯片再配上—个CD-ROM或DVD驱动器。现在,即使在很多廉价计算机上,多媒体部件也是作为标准设备。12.1 Multimedia519
  • 520. A sound card gives a computer the capability to record and play sound files as well as video sound tracks. Housed within the system unit, a sound card contains connectors that project from the back of the computer so that you can attach speakers, headphones, and a microphone. Expensive sound cards include circuitry for special audio effects, such as 3-D sound. The quality of your computer’s speakers and headphones can also affect the quality of the sound that you hear. 声卡为计算机提供了录制与放映声音文件的功能,作用类似于录音带。声卡安装在系统机箱内,它在计算机后面有一些突出的接口,可供用户将扬声器、耳机和麦克风插在上面。机器配置的扬声器和耳机的质量也会影响到你听到的音质。12.1 Multimedia520
  • 521. 12.1 MultimediaA CD-ROM drive allows your computer to access audio and software CD-ROMS. Multimedia elements—especially videos—require lots of storage space. Rather than store huge amounts of multimedia data on a computer’s hard disk, the data can be stored on a CD-ROM, which you insert only when you want to access the multimedia elements. A DVD drive can access multimedia data from CD-ROMs as well. A DVD also allows you to watch feature-length movies on your computer. CD-ROM驱动器允许计算机访问光盘内的音频和软件—特别是视频—需要大量的存储空间。人们并不把大量的多媒体数据存储在电脑硬盘上,而是存放在只读光盘上,只有需要访问多媒体数据时,才将光盘插入驱动器。一个DVD驱动器可以访问CD-ROM中的多媒体信息,也能让你在计算机上观赏高质量的电影。521
  • 522. 12.1 MultimediaYour computer’s graphics card takes signals from the processor and uses them to “paint” an image on the screen. A graphics card is installed inside the computer’s system unit and provides a connection for the monitor’s data cable. Your computer’s graphics card has to do a lot of work and must do it quickly. To display videos, for example, it repaints every pixel on the screen 15 times per second. More expensive “accelerated” graphics cards are equipped with circuitry that optimizes such tasks. 计算机的图形卡接收来自处理器的信号,并在屏幕上画出图形。图形卡安装在机器的机箱内,并提供调制解调器的数据电缆的接口。计算机的图形卡需要快速的做大量工作。比如,为了显示图像,每个像素每秒必须重画15次。为了优化此类工作,电路需安装更昂贵的加速图形卡。522
  • 523. A fast processor can quickly handle the huge amount of digital data that is required to store and produce multimedia. The faster the processor, the more data it can process each second. A computer with a fast processor outputs smooth video sequences with a sound track that is perfectly coordinated with the action. The popularity of multimedia has caused chipmakers to equip processor chips with special multimedia capabilities that speed up multimedia features such as sound and video. 一个快速处理器能快速处理需要存储并生成多媒体的大量数字数据。处理器越快,每秒处理的数据越多。配有快速处理器的计算机输出光滑的配有动作的声音影像。多媒体的流行使得芯片制造商开始配置具有特殊多媒体功能的处理器芯片,以加速声音和图像等多媒体性能。12.1 Multimedia523
  • 524. New Words & Expressions: Audio sound n.声音 retention n. 保留,保持 Static Graphics Images 静态图像 aid v. 援助,帮助 animation n. 动画 full-motion video 全运动影像12-2 ELEMENTS OF MULTIMEDIAAbbreviations : MIDI (Musical Instrument Digital Interface) 乐器数字接口 524
  • 525. 12-2 ELEMENTS OF MULTIMEDIAWe break the word multimedia into its component parts, we get multi -meaning more than one ,and media-meaning form of communication. Those types of media include: . Text . Audio Sound . Static Graphics Images . Animation . Full-Motion Video 如果我们把multimedia这个词分开,我们便得到multi——多,和media——媒体。媒体类型包括: · 文本 · 声音 · 静态图像 · 动画 · 动态视频 Logical Structures. Identifying these logical relationships is a job of the data administrator. A data definition language is used for this purpose. The DBMS may then employ one of the following logical structuring techniques during storage access, and retrieval operations [1]: 逻辑结构。确定这些逻辑关系是数据管理者的任务,由数据定义语言完成。DBMS在存储、访问和检索操作过程中可选用以下逻辑构造技术: 525
  • 526. 12-2 ELEMENTS OF MULTIMEDIAAll of the Above You can see that multimedia is by on means just one of the preceding technologies. Because of what hardware can and cannot do, it is often a trade-off between a certain number of static graphics images, audio sound, full-motion video and text. As you may guess, textual information takes the least amount of space to store. 总结 显然多媒体决不是一种从前的技术,由于硬件的能力要权衡选择静态图像、声音、全运动影像和文本,可以推测,文本信息占用存储空间最小。526
  • 527. 12-2 ELEMENTS OF MULTIMEDIAEven if a multimedia machine had unlimited resources, you would still want to add a combination of these multimedia technologies. For example, although a picture is worth a thousand words, it would be difficult to portray the work of William Shakespeare through pictures only. The same goes for audio sound. You could record the sound of church bells and a narration of the Bible, but at times you would rather have the Bible in textual format, which would allow you to search for certain key words. 即使多媒体机有无限的资源,人们仍想增加融这些多媒体技术于一体的综合技术。例如,尽管“一图胜千言”,但仍难以只用图像表述完莎士比亚的著作,仅用声音当然也不行。你可以记录教堂的钟声和圣经的叙述,但你仍愿使用文本形式的圣经,因为它可以使你查找某些关键词。527
  • 528. 12.3 The Multimedia Personal ComputerNew Words & Expressions business strength 具有事务处理能力的 chore n. 家务杂事 arcade 带拱顶街道 unleash v. 释放 playback v. 重播,读出 synthesizer n. 综合器,合成器 mixer n.混合者,搅拌器 thruport n. 吞吐量 buzzword n. 时髦词语,漂亮口号 jargon n. 行话,术语 frame n. 帧 jerky a. 急拉的,急动的 Abbreviations: MPC (Multimedia Personal Computer) 多媒体个人计算机 CD-ROM (Compact Disc-Read Only Memory) 光盘只读存储器 MIDI (Musical Instrument Digital Interface) 乐器数字接口528
  • 529. 12.3 The Multimedia Personal Computer What is MPC? MPC stands for “multimedia personal computer”. The requirements for an MPC are described in detail in Microsoft’s Multimedia PC Specification Version 1.0. here are the key elements of the specification: BASE SYSTEM: a Windows-capable [2] system with a 10-MHz 286 or faster CPU; at least 2MB of RAM; a 30 MB or larger hard disk; a 3.5-inch 1.44 MB floppy drive; a 101-key keyboard; a two-button mouse; and parallel, serial, and joystick ports. 什么是MPC?MPC是指“多媒体个人计算机”。 Microsoft公司的“多媒体PC机规范1.0版”一书对MPC机进行了详细描述。以下是此规范的要求: 基本系统:一个能运行Windows的系统。它采用10MHz时钟的286或速度更快的CPU;至少有2兆字节的RAM;30兆字节或更大的硬盘空间;3.5英寸1.44兆字节的软盘驱动器;101键盘;两按钮的鼠标器以及并行、串行的控制杆端口。529
  • 530. 12.3 The Multimedia Personal Computer VIDEO: standard VGA is all that’s required; CD-ROM: a CD-ROM drive that transfers at least 150 K of data per second without taking up more than 40 percent of the CPU’s attention, play CD audio, and has an average access time of 1 second or less. AUDIO: a sound board with 8-bit, 11.025-kHz sampling and 22.05-kHz playback; a synthesizer capable of playing eight notes simultaneously using five different sounds; a mixer to combine CD audio, sampling, and synth; a microphone input; and MIDI in, out, and thruports. 视频:标准的VGA显示器即可。 CD-ROM:要求CD-ROM光驱的数据传输速率至少为每秒150 K,不能占用40%以上的CPU时间,能播放CD,平均存取时间为1秒或更短。 音频功能:一块8位的、11.025kHz取样和22.05kHz回放的声卡;能同时放8个使用5种不同音色的音律的合成器;能把光盘音频、取样和合成声音混合起来的混声器;麦克风输入;MIDI(乐器数字接口)输入、输出和通路。530
  • 531. 12.3 The Multimedia Personal Computer Every new technology has its own buzzwords, and sorting them out can be real detective work. The following is two jargons of MPC. FULL-MOTION VIDEO: Full-motion video is digitally recorded video played back at the broadcast standard of 30 frames per second, or close enough to that speed so the video appears smooth rather than jerky. MIDI: MIDI is short for Musical Instrument Digital Interface, a standard specification developed by music synthesizer manufacturers. The concept of being able to control several instruments from one keyboard has grown into a method for putting musical instruments, tape recorders, VCRs, mixers, and even stage-lighting under the control of a single computer. 每一种新技术都有它自己的术语,将它们进行分类是一项非常精细的工作,下面是MPC的两个术语。 全运动图像:全运动图像是以数字方式记录的视频图像,以每秒30帧的电视广播标准或者非常接近于此的速度重现图像,因而这些视频图像看上去很自然,没有跳跃感。 MIDI:MIDI是乐器数字接口的缩写。它是由音乐合成器制造商开发的标准规范。从一个键盘能控制几个乐器的想法已变为现实,它能把乐器、磁带录音机、录像机、混声器、甚至舞台灯光等置于单台计算机的控制之下。531
  • 532. 英文摘要(Abstract)的写作应用很广。论文摘要是全文的精华,是对一项科学研究工作的总结,对研究目的、方法和研究结果的概括。 一、摘要的种类与特点 摘要主要有以下四种。 第一种是随同论文一起在学术刊物上发表的摘要。这种摘要置于主体部分之前,目的是让读者首先了解一下论文的内容,以便决定是否阅读全文。一般来说,这种摘要在全文完成之后写。字数限制在100~150字之间。内容包括研究目的、研究方法、研究结果和主要结论。 第二种是学术会议论文摘要。会议论文摘要往往在会议召开之前几个月撰写,目的是交给会议论文评审委员会评阅,从而决定是否能够录用。所以,比第一种略为详细,长度在200—300字之间。会议论文摘要的开头有必要简单介绍一下研究课题的意义、目的、宗旨等。如果在写摘要时,研究工作尚未完成,全部研究结果还未得到,那么,应在方法、目的、宗旨、假设等方面多花笔墨。英文摘要的写作技巧 532
  • 533. 英文摘要的写作技巧第三种为学位论文摘要。学士、硕士和博士论文摘要一般都要求用中、英文两种语言写。学位论文摘要一般在400字左右,根据需要可以分为几个段落。内容一般包括研究背景、意义、主旨和目的;基本理论依据,基本假设;研究方法;研究结果;主要创新点;简短讨论。不同级别的学位论文摘要,要突出不同程度的创新之处,指出有何新的观点、见解或解决问题的新方法。 第四种是脱离原文而独立发表的摘要。这种摘要更应该具有独立性、自含性、完整性。读者无需阅读全文,便可以了解全文的主要内容。533
  • 534. 英文摘要的写作技巧二、摘要的内容与结构 摘要内容一般包括: Ø         目的(objectives,purposes):包括研究背景、范围、内容、要解决的问题及解决这一问题的重要性和意义。 Ø         方法(methods and materials):包括材料、手段和过程。 Ø         结果与简短讨论(results and discussions):包括数据与分析。 Ø         结论(conclusions):主要结论,研究的价值和意义等。 概括地说,摘要必须回答“研究什么”、“怎么研究”、“得到了什么结果”、“结果说明了什么”等问题。 无论哪种摘要,语言特点和文体风格也都相同。首先必须符合格式规范。第二,语言必须规范通顺,准确得体,用词要确切、恰如其分,而且要避免非通用的符号、缩略语、生偏词。另外,摘要的语气要客观,不要做出言过其实的结论。534
  • 535. 英文摘要的写作技巧三、学术期刊论文摘要 1、摘要的目的 摘要是论文的梗概,提供论文的实质性内容的知识。摘要的目的在于:给读者关于文献内容的足够的信息,使读者决定是否要获得论文。 2、摘要的要素 1)       目的——研究、研制、调查等的前提、目的和任务,所涉及的主题范围。 2)       方法——所用的原理、理论、条件、对象、材料、工艺、结构、手段、装备、程序等。 3)       结果——实验的、研究的结果、数据,被确定的关系,观察结果,得到的效果、性能等。 4)      结论——结果的分析、研究、比较、评价、应用,提出的问题等。 3、摘要的篇幅 摘要的篇幅取决于论文的类型。但无论哪一种论文,都不能超过150 words。 535
  • 536. 英文摘要的写作技巧4、摘要的英文写作风格(公认的英文摘要写作规范) 1)         句子完整、清晰、简洁。 2)         用简单句。为避免单调,改变句子的长度和句子的结构。 3)         用过去时态描述作者的工作,因它是过去所做的。但是,用现在时态描述所做的结论。 4)         避免使用动词的名词形式。如: 正:“Thickness of plastic sheet was measured” 误:“measurement of thickness of plastic sheet was made” 5)         正确地使用冠词,既应避免多加冠词,也应避免蹩脚地省略冠词。如: 正:“Pressure is a function of the temperature” 误:“The pressure is a function of the temperature”; 536
  • 537. 英文摘要的写作技巧4、摘要的英文写作风格 6)         使用长的、连串的形容词、名词、或形容词加名词来修饰名词。为打破这种状态,可使用介词短语,或用连字符连接名词词组中的名词,形成修饰单元。例如: 应写为“The chlorine-containing propylene-based polymer of high melt index”, 而不写为“The chlorine containing high melt index-propylene based polymer” 7)         使用短的、简单的、具体的、熟悉的词。不使用华丽的词藻。 8)         使用主动语态而不使用被动语态。“A exceeds B”读起来要好于“B is exceeded by A”。使用主动语态还有助于避免过多地使用类似于“is”, “was”, “are”和“were”这样的弱动词。537
  • 538. 英文摘要的写作技巧4、摘要的英文写作风格 9)         构成句子时,动词应靠近主语。避免形如以下的句子: “The decolorization in solutions of the pigment in dioxane, which were exposed to 10 hr of UV irradiation, was no longer irreversible.” 改进的句子,应当是: “When the pigment was dissolved in dioxane, decolorization was irreversible, after 10 hr of UV irradiation.” 10)      避免使用那些既不说明问题,又没有任何含意的短语。例如: “specially designed or formulated”,“ The author discusses”, “The author studied” 应删去。 不使用俚语、非英语的句子,慎用行话和口语,不使用电报体。 538
  • 539. Computer English Chapter 13 Computer Graphics
  • 540. Key points: concept of computer graphics Difficult points: Applications of computer graphics540
  • 541. Requirements:Concept of computer graphics 2. Applications of computer graphics.3. Example of analogue device and digital device4掌握求职英语的写法541
  • 542. New Words & Expressions: via 经,通过 conversation n. 会话,交谈 adage n. 谚语,格言 pervade 蔓延,遍及,扩大 diverse a. 不同的 encompass v. 包括,包含 adopt v. 采用,采纳 image n. 图像 classify vt. 分类 simulation n. 模拟,仿真 span v.横越,跨越 orthographic projections 八面图形投影法 perspective a. 透视的 Renaissance n. 文艺复兴 plot v. 绘图,划分 intractable a. 难解决的13.1 Introduction To Computer Graphics Abbreviations: CRT(Cathode-ray tube) 阴极射线管 542
  • 543. The use of computer graphics pervades many diverse fields. Applications range from the production of charts and graphs, to the generation of realistic images for television and motion pictures to the interactive design of mechanical parts [1] .To encompass all these uses, we can adopt a simple definition: 计算机图形学的应用扩展到了许多不同领域,应用的范围从表和图形的产生,到用于电视和动画片的真实图像的生成,到机械零件的交互式设计。我们采用一个简单的定义来概括所有这些应用: Computer graphics is concerned with all aspects of using a computer to generate images. “计算机图形学主要研究采用计算机生成图像的所有方面。”13.1 Introduction To Computer Graphics543
  • 544. We can classify applications of computer graphics into four main areas: ·           Display of information ·           Design ·           Simulation ·           User interfaces 我们可以把计算机图形学的应用分作四个主要方面: · 信息显示 · 设计 · 模拟 · 用户界面 13.1 Introduction To Computer Graphics544
  • 545. 13.1.1 Display of information Graphics has always been associated with the display of information. Examples of the use of orthographic projections to display floorplans of buildings can be found on 4000-year-old Babylonian stone tablets. 13.1.1 信息显示 图形总是和信息显示相联系的。4000年以前在巴比伦发现了在石桌上用八面图形投影法去表现建筑平面设计图的例子。 Medical imaging uses computer graphics in a number of exciting ways. 医学图像也运用计算机图形学解决了大量难题。13.1 Introduction To Computer Graphics545
  • 546. 13.1.2 Design Professions such as engineering and architecture are concerned with design. Although their applications vary, most designers face similar difficulties and use similar methodologies. One of the principal characteristics of most design problems is the lack of a unique solution. Hence, the designer will examine a potential design and then will modify it, possibly many times, in an attempt to achieve a better solution. Computer graphics has become an indispensable element in this iterative process. 工程和建筑的专业人员关心设计,尽管他们的应用不同,但大多数设计者面对相似的困难,采用了类似的方法。大多数设计问题的基本特点之一是缺少唯一的解决方案,因此,设计者可能需要多次检查原来的设计,修改它,以获得一个更好的解决方案。在这个重复的过程中,计算机图形学已变成一个不可缺少的部分。13.1 Introduction To Computer Graphics546
  • 547. 13.1.3 Simulation Some of the most impressive and familiar uses of computer graphics can be classified as simulations. Video games demonstrate both the visual appeal of computer graphics and our ability to generate complex imagery in real time. The insides of an arcade game reveal state-of-the-art hardware and software. Computer-generated images are also the heart of flight simulators, which have become the standard method for training pilots. The savings in dollars and lives realized from use of these simulators has been enormous. The computer-generated images we see on television and in movies have advanced to the point that they are almost indistinguishable from real-world images. 13.1.3 模拟 最为人所知的计算机图形学应用可归为模拟类。视频游戏展示了计算机图形学的视觉魅力和我们实时生成复杂图像的能力。走廊游戏的内容揭示了当前软件和硬件的技术发展水平。计算机生成的图像是飞行模拟器的核心,已经成为训练飞行员的标准方法,这种模拟训练大大节省了人力物力。我们在电视和电影中看到的计算机生成的图像已经达到了和真实图像几乎无法区分的地步。13.1 Introduction To Computer Graphics547
  • 548. 13.1.4 User Interfaces The interface between the human and the computer has been radically altered by the use of computer graphics. Consider the electronic office. The figures in this book were produced through just such an interface. A secretary sits at a workstation, rather than at a desk equipped with a typewriter. This user has a pointing device, such as a mouse, that allows him to communicate with the workstation. The display consists of a number of icons that represent the various operations the secretary can perform. For example, there might be an icon of a mailbox that ,if pointed to and clicked on ,causes any electronic-mail messages to appear on the screen. 计算机图形学的应用已经根本改变了人和计算机之间的界面。讨论一下电子办公室,本书的图是由这样的界面产生的,秘书坐在工作站前,而不是备有打字机的办公桌前,这一用户有一个指示设备(如鼠标)实现他和工作站之间的交互。显示由许多图符组成,代表秘书可进行的各种操作,例如,有一个邮箱图符,如果指向并点击它,屏幕上将会显示电子邮件信息.13.1 Introduction To Computer Graphics548
  • 549. New Words & Expressions: video monitor 视频监视器 solid-state 固态(使用电晶体不用真空管)的 predominant 支配的 raster-scan display 光栅扫描显示器 frame buffer 帧缓冲器 intensity n. 强度 pixel (or pel) n. 像素 resolution n. 分辨率 bitmap n. 位图 random-scan display 随机扫描显示器 vector 矢量,向量 hard-copy device 硬拷贝设备 pen plotter 笔式绘图仪 flat-panel displays 平板显示器 rugged 粗糙的,要求不高的13.2 Video Display Devices Abbreviations : CRT(cathode-ray-tube) 阴极射线管 DVST(Direct-View Storage Tube) 直视存储管549
  • 550. 13.2 Video Display Devices Raster-Scan Displays The most common type of graphics monitor employing a CRT is the raster-scan display, based on television technology [1]. In a raster-scan system, the electron beam is swept across the screen, one row at a time from top to bottom. As the electron beam moves across each row, the beam intensity is turned on and off to create a pattern of illuminated spots. 光栅扫描显示器 使用CRT的普通图形监视器是基于电视技术的光栅扫描显示器。在光栅扫描系统中,电子束横向扫描屏幕,一次一行,从顶到底依次进行。当电子束沿横向逐行移动时,电子束的强度不断变化,从而建立亮点的可显示模式。 550
  • 551. 13.2 Video Display Devices Raster-Scan Displays Picture definition is stored in a memory area called the refresh buffer or frame buffer. This memory area holds the intensity values for all the screen points. Stored intensity values are then retrieved from the frame buffer and “ painted” on the screen one row (scan line) at a time. Each screen point is referred to as a pixel or pel (shortened forms of picture element). The capability of a raster-scan system to store intensity information for each screen point makes it well suited for the realistic display of scenes containing subtle shading and color patterns. Home television sets and printers are examples of other systems using raster-scan methods. 图形定义保存在称为刷新缓冲器或帧缓冲器的存储器中。该存储器保存一组对应屏幕所有点的强度值。然后再从刷新缓冲器取出存储的强度值,并在屏幕上逐行(扫描行)画出。每个屏幕点作为一个像素。光栅扫描系统对于屏幕每一点都有存储强度信息的能力,从而使之较好地适用于包含细微阴影和彩色模式的场景的逼真显示。家用电视和打印机是另一类使用光栅扫描方式的例子。551
  • 552. 13.2 Video Display Devices Random-Scan Displays When operated as a random-scan display unit, a CRT has the electron beam directed only to the parts of the screen where a picture is to be drawn. Random-scan monitors draw a picture one line at a time and for this reason are also referred to as a vector displays(or stroke-writing or calligraphic displays). The component lines of a picture can be drawn and refreshed by a random-scan system in any specified order. A pen plotter operates in a similar way and is an example of a random-scan, hard-copy device. 随机扫描显示器 当使用随机扫描显示器时,CRT的电子束只在屏幕的图形部分移动。随机扫描显示器一次只绘制图形中的一条线,因此也称为向量显示器(或笔划显示器,或笔迹显示器)。图形的组成线条由随机扫描系统按任意指定的顺序绘制并刷新。笔式绘图仪也以类似的方式工作,它是随机扫描、硬拷贝设备的一个例子。552
  • 553. 13.2 Video Display Devices Direct-View Storage Tubes An alternative method for maintaining a screen image is to store the picture information inside the CRT instead of refreshing the screen. A direct-view storage tube (DVST) stores the picture information as a charge distribution just behind the phosphor-coated screen [3]. Two electron guns are used in a DVST. One, the primary gun, is used to store the picture pattern; the second, the flood gun, maintains the picture display. 直视存储管 保持屏幕图形的另一种方法是把图形信息存储在CRT内,而不再是刷新屏幕。直视存储管(DVST)通过紧贴在屏幕荧光层后的电荷分布来存储图形信息。DVST使用两支电子枪。一支是基本枪,用来存储图形图案;另一支是泛流枪,用来保持图形显示。553
  • 554. 13.2 Video Display Devices Flat-Panel Displays The term flat-panel display refers to a class of video devices that have reduced volume, weight, and power requirements compared to a CRT. A significant feature of flat-panel displays is that they are thinner than CRTs, and we can hang them on walls or wear them on our wrists. Since we can even write on some flat-panel displays, they will soon be available as pocket notepads. Current uses for flat-panel displays include small TV monitors, calculators, pocket video games, laptop computers, armrest viewing of movies on airlines, as advertisement boards in elevators, and as graphics displays in applications requiring rugged, portable monitors. 平板显示器 平板显示器代表一类能比CRT减少体积、减轻重量并节省功耗的视频设备。平板显示器的一个有意义的特性是比CRT要薄,可把它们挂在墙上或戴在手腕上。因为有些平板显示器上甚至可以书写,不久它们即可作为袖珍式笔记本。平板显示器目前的应用包括小型TV监视器、计算器、袖珍式视频游戏机、折叠式计算机、航空座椅上的电影屏幕、电梯内的告示牌,以及在要求不高的便携式监视器的应用场合中,作为图形显示器。554
  • 555. 13.3 Output PrimitivesNew Words & Expressions output primitives 输出图元 analog device 模拟设备 vector n. 矢量 pen plotter 笔式绘图仪 random-scan display 随机扫描显示器 endpoint n. 端点 horizontal a. 水平的 vertical a. 垂直的 deflection n. 偏转,偏差 voltage n. 电压,伏特数 digital device 数字设备 high-resolution 高分辨率的555
  • 556. 13.3 Output Primitives Typically, graphics programming packages provide functions to describe a scene in terms of these basic geometric structures, referred to as output primitives, and to group sets of output primitives into more complex structures [1]. Each output primitive is specified with input coordinate data and other information about the way that the object is to be displayed. Points and straight-line segments are the simplest geometric components of pictures. Additional output primitives that can be used to construct a picture include circles and other conic sections, quadric surfaces, spline curves and surfaces, polygon color areas, and character strings. 通常,图形编程软件包提供了一些功能来描述场景,这些功能使用了称为输出图元的基本几何结构并将输出图元组合成更复杂的结构。每个输出图元是由输入的坐标数据和有关物体显示的一些信息来指定。点和直线是最简单的几何成分,其它可以用来构造图形的输出图元有:圆及其它圆锥曲线、二次曲面、样条曲线和曲面、多边形填色区域以及字符串等。 556
  • 557. 13.3 Output Primitives Points and Lines Point plotting is accomplished by converting a single coordinate position furnished by an application program into appropriate operations for the output device in use. With a CRT monitor, for example, the electron beam is turned on to illuminate the screen phosphor at the selected location. How the electron beam is positioned depends on the display technology. 点和线 通过将应用程序提供的单个坐标位置转换成输出设备的相应操作,可以进行点的绘制。例如,对于CRT监视器,则是打开电子束,从而在选中的位置上照亮屏幕的荧光层。电子束的定位方法取决于显示技术。557
  • 558. 13.3 Output Primitives Points and Lines Line drawing is accomplished by calculating intermediate positions along the line path between two specified endpoint positions. An output device is then directed to fill in these positions between the endpoints. For analog devices, such as a vector pen plotter or a random-scan display, a straight line can be drawn smoothly from one endpoint to the other. Linearly varying horizontal and vertical deflection voltages are generated that are proportional to the required changes in the x and y directions to produce the smooth line. 通过计算沿线路径上两指定端点间的中心位置,可以绘制一条线段,输出设备则按指令在端点间的这些位置直接填充。对于笔式绘图仪或随机扫描显示器这类模拟设备,可以从一个端点至另一端点绘制光滑线段。这是根据x方向和y方向需要修改的实际量,线性地改变水平和垂直偏转电压而实现的。558
  • 559. 13.3 Output Primitives Points and Lines To load a specified color into the frame buffer at a position corresponding to column x along scan line y, we will assume we have available a low-level procedure of the form setPixel (x, y) 为了将对应于扫描线y、列x的位置上指定的颜色装入帧缓冲器,我们假设有如下形式的低层程序: setPixel (x, y) We sometimes will also want to be able to retrieve the current frame-buffer intensity setting for a specied location. We accomplish this with the low-level functon GetPixel (x, y) 有时,我们也要求能提取某个特定位置的当前帧缓冲器的强度设置,可以使用下列低层函数来完成: getPixel (x, y)559
  • 560. 13.3 Output Primitives FILL-AREA FUNCTIONS We display a filled polygon in PHIGS and GKS with the function fillArea (n, wcVertices) The displayed polygon area is bounded by a series of n straight line segments connecting the set of vertex positions specified in wcVertices. These packages do not provide fill functions for objects with curved boundaries. 区域填充函数 在PHIGS和GKS中,利用下列函数显示填充的多边形: fillArea (n, wcVertices) 显示的多边形区域,由一系列在wcVertices中指定的顶点连接起来的n条直线段包围。这些软件包没有提供曲线边界对象的填充功能。560
  • 561. New Words & Expressions: animation n. 动画 imply v. 暗指,暗示 visual a. 视觉的 scene n. 场景,情景 translation n. 平移 rotation n. 旋转 variation n. 变化 transparency n. 透明性 surface texture 表面纹理 automobile n.〈主美〉汽车 engine n. 引擎 orientation n. 方向,方位,定位 focal length 焦距 lighting effect n. 光照效果 illumination n. 照明 rendering n. 着色,绘画 storyboard n. 剧本 layout n. 布置,版面安排 key-frame 关键帧 in-between frames n. 插值帧 frame-by-frame a. 逐帧的 consecutively adv. 连续地,连贯的 13.4 Computer Animation561
  • 562. 13.4 Computer Animation Some typical applications of computer-generated animation are entertainment (motion pictures and cartoons), advertising, scientific and engineering studies, and training and education. Although we tend to think of animation as implying object motions, the term computer animation generally refers to any time sequence of visual changes in a scene. In addition to changing object position with translations or rotations, a computer-generated animation could display time variations in object size, color, transparency, or surface texture. 计算机生成动画的代表性应用有娱乐(电影和卡通片)、广告、科学和工程研究以及培训和教学。尽管我们在考虑动画时暗指对象的移动,但术语“计算机动画”通常指场景中任何随时间而发生的视觉变化。除了通过平移、旋转来改变对象的位置外,计算机生成的动画还可以随时间进展而改变对象大小、颜色、透明性和表面纹理等。 562
  • 563. 13.4 Computer Animation Design of Animation Sequences In general, a sequence is designed with the following steps: ·           Storyboard layout ·           Object definitions ·           Key-frame specifications ·           Generation of in-between frames 动画序列的设计 通常,一个动画序列按照以下几步进行设计: 故事情节拆分 对象定义 关键帧描述 插值帧的生成563
  • 564. 13.4 Computer Animation Design of Animation Sequences The storyboard is an outline of the action. It defines the motion sequence as a set of basic events that are to take place. Depending on the type of animation to be produced, the storyboard could consist of a set of rough sketches or it could be a list of the basic ideas for the motion. 剧本是动作的轮廓。它将动画序列定义为一组要发生的基本事件。依赖于要生成的动画类型,剧本可能包含一组粗略的草图或运动的一系列基本思路。564
  • 565. 13.4 Computer Animation Design of Animation Sequences A key frame is a detailed drawing of the scene at a certain time in the animation sequence. Within each key frame, each object is positioned according to the time for that frame. Some key frames are chosen at extreme positions in the action; others are spaced so that the time interval between key frames is not too great. More key frames are specified for intricate motions than for simple, slowly varying motions. 一个关键帧是动画序列中特定时刻的一个场景的详细图示。在每一个关键帧中,每一个对象的位置依赖于该帧的时刻。选择某些关键帧作为行为的极端位置。另一些则以不太大的时间间隔进行安排。对于复杂的运动,要比简单的缓慢变化运动安排更多的关键帧。565
  • 566. 13.4 Computer Animation In-betweens are the intermediate frames between the key frames. The number of in-betweens needed is determined by the media to be used to display the animation. Film requires 24 frames per second, and graphics terminals are refreshed at the rate of 30 to 60 frames per second. Typically, time intervals for the motion are set up so that there are from three to five in-betweens for each pair of key frames. Depending on the speed specified for the motion, some key frames can be duplicated. For a 1-minute film sequence with no duplication, we would need 1440 frames. With five in-betweens for each pair of key frames, we would need 288 key frames. If the motion is not too complicated, we could space the key frames a little farther apart. 插值帧是关键帧之间过渡的帧。插值帧的数量取决于用来显示动画的介质。电影胶片要求每秒24帧,而图形终端按每秒30到60帧来刷新。一般情况下,运动的时间间隔设定为每一对关键帧之间有3~5个插值帧。依赖于为运动指定的速度,有些关键帧可重复使用。一分钟没有重复的电影胶片需要1440帧。如果每两个关键帧之间有5个插值帧,则需要288幅关键帧。如果运动并不是很复杂,我们可以将关键帧安排得稀一点。566
  • 567. 13.4 Computer Animation General Computer-Animation Functions Some steps in the development of an animation sequence are well suited to computer solution, These include object manipulations and rendering, camera motions, and the generation of in-betweens. Animation packages, such as Wave-front, for example, provide special functions for designing the animation and processing individual objects. Another typical function simulates camera movements. Standard motions are zooming, panning, and tilting. Finally, given the specification for the key frames, the in-betweens can be automatically generated. 通用计算机动画功能 开发动画序列中的某几步工作很适合计算机进行处理。其中包括对象管理和绘制、照相机运动和生成插值帧。动画软件包,如Wavefront,提供了设计动画和处理单个对象的专门功能。 另一种典型功能是模拟照相机的运动,标准的运动有拉镜头、摇镜头和倾斜。最后,给出对关键帧的描述,然后自动生成插值帧。567
  • 568. 一、个人简历 个人简历(resume / curriculum vitae)是升学、求职过程中的重要文件。英文个人简历的格式比较固定,一般应包括个人信息、联系地址、求职愿望、学历、工作经历、证明人等部分,也可以根据具体情况,适当增加有关条目。内容的安排要求清晰易读、层次分明,学历和工作经历一般可从最近开始,逐渐向后追述。从语言方面来看,个人简历多以名词词组为主,也可以使用动词词组,但是要求结构整齐对称。 以下是某位学生的个人简历,他申请的工作职位是某计算机公司的售后服务技术员。一般来说,他还需另外撰写一份求职信,介绍一下本人的基本情况、特长及对该公司业务的熟悉程度,同时重申个人的工作愿望,并提出面试请求。求职英语简介568
  • 569. 一、个人简历 Resume Personal details Name: Li Jian Age: 20 Date of Birth: May 21,1981 Marital Status: single Address: 36 Yanshan Street, Jinan, Shandong 250014, P. R. China Tel: 0531-8937777 E-mail: lijian@hotmail.com Position applied for After-sale Service Technician求职英语简介569
  • 570. 一、个人简历 Education: September 1995 to present Shandong Institute of Electronic Technology, Major in Applied Computing with special interest in networking & website implementation. Courses taken: C Programming, Software Engineering, Visual Foxpro, Microsfot Office, Data Structures in C, English for Computing, Computer Networks, Internet Application, etc. September 1992 to July 1995 Jinan No.14 Middle School, Jinan, Shandong. Monitor of class, outstanding in math & physics.求职英语简介570
  • 571. 一、个人简历 Work experience: Summer 1998 Company: ABC Computer Corp. Post: Sales Promotion Responsibility: organizing product exhibition tours & market survey. Summer 1997 Company: Hope Co., Ltd Post: System Integration Responsibility: assembling PCs according to customer requirements; fixing hardware problems; on-the-spot installation & testing. Summer, 1996 Company: Eastsoft Co., Ltd Post: Reception Responsibility: understanding customer needs; explaining Eastsoft products & services; highlighting Eastsoft after-sale service.求职英语简介571
  • 572. 一、个人简历 Honors Top Prize in Homepage Design Contest, 1998. Other information Fluent in English with a TOEFL score of 590. References Mr. Liu Xinhua Ms. Wang Ying Sales Manager Manager of Customer Relations ABC Computer Corp. Eastsoft Co., Ltd 38 Heping Street 135 Wenhua Avenue Jinan, Shandong, 250014 Jinan, Shandong 250014 P. R. China P. R. China求职英语简介572
  • 573. 二、求职申请信 一般来讲,求职信主要应包括以下几项内容: (1) 点明你所要申请的工作职位; (2) 说明你从何得知这份工作的信息(如从同事朋友处或从报纸的招聘广告等); (3) 引起招聘者对简历中相关内容的注意; (4) 说明你是此项工作的最佳人选。 前两项通常在信函的第一段中开门见山加以说明。后两项是申请信的主要内容,放在第二段。本段表达成功与否起着很重要的作用,对求职者的能力和个性也是一种检验。在写作时,应指出你的简历中与工作特别相关的内容,以引起招聘者的注意和兴趣。在求职信的收尾段中,应说明联络方式并表达希望得到面试的机会。求职英语简介573
  • 574. 二、求职申请信 (求职范例-谋求证券经纪人之职) Gentlemen: Your advertisement for stockbrokers in “China Daily” of May 2 has interested me very much. I feel I can fit one of the vacancies you have. I am twenty-two years of age and female. I will graduate in July. My specialty at college is none other than securities business. I have gained some practical experience in brokerage in recent years acting as a part-time broker for Beijing Commodities Futures Exchange. At college, I have participated in a lot of activities both at the collegiate level and the departmental level. I have attended a large number of symposia and conferences on the business of stockbroking. I am young and energetic and maintain good interpersonal relations. I mention these because I know my line off work is a demanding one and I am willing to show that I can face up to any challenge placed before me. Should this application meet with your favorable consideration, I will do my utmost to satisfy the confidence you may repose in me. I am looking forward to hearing from you as soon as possible. Faithfully yours, Jing Jimei Enclose: (1) My resume (2) My academic record (3) Two recent photos求职英语简介574
  • 575. 二、求职申请信 (求职范例-谋求证券经纪人之职) 本人对贵公司五月二日在《中国日报》上招聘证券经纪人的广告极感兴趣。我认为本人可以填补贵公司其中一个空缺的职位。 我现年22岁,女性,即将于7月份毕业。我在大学所学专业正是证券交易。近两年来,我为北京商品期货交易所当兼职经纪人,从中获得了一些经纪方面的实际经验。我在学校参加了许多活动,既有学校级的,也有高一级的。我还参加了不少以股票买卖为专题的研讨会和会议。本人精力充沛,而且有良好的人际关系。我之所以提及这些是因为我知道这种工作是要求很严的工作,但是我愿意面对出现在我面前的任何挑战。 贵公司如对我的申请惠予考虑,本人将竭诚工作,以不负贵公司之愿望。期望你们尽早回复。 附件: (1) 个人简历 (2) 成绩单 (3) 两张近照求职英语简介575
  • 576. Computer English Chapter 14 Virtual Reality
  • 577. Key points: useful terms and definitions of Virtual Reality Difficult points: applications and features of VRML577
  • 578. Requirements:Concept of virtual reality 2. Applications of VRML3. Describe the features of VRML4. 了解广告文体的特点578
  • 579. New Words & Expressions: presentation 陈述,表达 multisensory adj. 多感官的 perspective 透视图,观点 illusion n. 幻想 image 影像,图像 inherently 天性地,固有地 six-surface Cube 六面体 real-time 实时的 stereo 立体的,立体感觉的 resolution n.. 分辨率 mount v. 装配,安装 release v. 释放,放弃 depth cue 深度暗示 projected adj. 投影的 visual adj. 视觉的 simulation n. 模拟14.1 An Introduction to and History of Virtual Reality Abbreviations: VR (Virtual Reality) 虚拟现实 BOOM(Binocular Omni-Orientation Monitor) 双目全方位监视器 HMD (head-mounted display) 头盔显示器579
  • 580. One definition of virtual reality is a wide-field presentation of computer-generated, multisensory information that tracks a user in real time. This definition is used at the Electronic Visualization Laboratory in Chicago (EVL[1]). In other words, virtual reality[2] means that the user is surrounded by a computer-generated image that changes depending on the movements—i.e.shifts in perspective—of the user. 虚拟现实的定义之一:虚拟现实是对由计算机生成的、能够实时追踪用户的多感官信息的一种笼统表述。芝加哥电子可视化实验室(EVL)采用的就是这种定义。换句话说,虚拟现实意味着用户被计算机生成的图景所包围,这些图景要依据用户的运动(如视角的转换)而产生变化。14.1 An Introduction to and History of Virtual Reality 580
  • 581. The first attempt at virtual reality used head-mounted displays (HMDs). In HMDs, projectors feed real-time images to small screens attached inside a kind of helmet that the user wears. In the beginning, HMDs often showed mono pictures, and the user’s head movements were tracked. In modern HMDs, stereo pictures are standard, since the technique has become cheaper. Typically, HMDs either have poor resolution or are too heavy. Because only one person at a time can use an HMD, discussion of images is much more difficult. 虚拟现实首次尝试使用了头盔式显示器(HMD)。在HMD中,投影机把实时图景投影到附着于用户所带头盔内的小屏幕上。最初,HMD显示平面图片,追踪用户的头部运动。但在现代HMD中,由于这项技术变得更加便宜,立体图片则成为了标准。通常说来,HMD或者分辨率过低或者过于笨重。由于一个HMD一次只能由一个人使用,因此对图景的讨论就更加困难。14.1 An Introduction to and History of Virtual Reality 581
  • 582. To increase image quality, Fakespace[4] invented the BOOM (Binocular Omni-Orientation Monitor).Very small monitors are mounted on a mechanical arm, and users look into the monitors like they would look into a pair of binoculars. Tracking occurs when the user moves the arm, which changes the perspective. When a user releases the BOOM, another person can look at the same thing from the same perspective, which is an advantage over HMDs. Since real monitors are used, the resolution is good. 为了提高图景的质量,Fakespace发明了BOOM(双目全方位监视器)。机械臂上固定着非常小的监视器,就象使用双目望远镜一样,用户使用监视器观察。用户移动机械臂时改变了视角,因此实现了追踪。当一个用户不用这个BOOM后,另一个用户可以从相同的视角观察到相同的事物,这一点BOOM要优于HMD。因为使用了真正的监视器,所以分辨率很好。14.1 An Introduction to and History of Virtual Reality 582
  • 583. The concept of a room with graphics projected from behind the walls was invented at EVL in 1992. The images on the walls are usually in stereo to give a depth cue. The main advantage over ordinary graphics systems is that the users are surrounded by the projected images, which means that the images are the users’main field of vision. This is usually called a “CAVE”,CAVE Automatic Virtual Environment. The first CAVE(as well as the concept) was created by the faculty, staff, and students at EVL. 具有墙后投影生成图像的房间的概念是1992年在EVL发明的。墙上的图景通常是立体的以便能表现出深度。与普通的图形系统相比,它的主要优势在于用户被投影图像所包围,这意味着这些图景是用户的主要视野。它通常被称为CAVE,即洞穴式自动虚拟环境。第一台CAVE(与其概念)是由EVL的全体教职员和同学共同创造的 14.1 An Introduction to and History of Virtual Reality 583
  • 584. New Words & Expressions: interactive 交互的 intranet n. 企业内部互联网 integrate 使成整体,结合 visualization n. 可视化 presentation n. 演示 virtual adj. 虚拟的 criteria 准则 authorability n, 创作性 compose 组成,写作,排字 re-usability n. 可重用性 extensibility 可扩展性 explicitly 明白地,明确地 platform 平台 arbitrarily 武断地,任意地 static 静态的 animated 动画的,活生生的 dynamic 动态的 hyperlink 超级联接 author v. 制作 available 可利用的 registration 注册,登记 community 团体,公用 interoperable 能共同使用的 extension n. 延长,范围 scope 范围 specification 规范,说明书 14.2 About VRML 584
  • 585. New Words & Expressions: conceptually 概念地 aural 听觉的 modify 更改,修改 mechanisms 机制 primary 原始的 composition 合成法,排版 encapsulation 封装 semantic 语义 resolution 分辨率 latitude 纬度,范围,地区 interpretation 解释,阐明 mouse 鼠标 implicitly 含蓄地,暗中地 coordinate 坐标 recursively 递归地,回归地 sphere 球体 reference 提及,参考书目 enclose 放入,封闭,包装 hierarchical 分层的,层次的 spatial adj. 空间的 accumulation 积聚,积累 dissipate v. 使消失,失去 intractable 难处理的 compact 紧凑的,简洁的 syntax n. 语法14.2 About VRML 585
  • 586. 14.2 About VRML Abbreviations : VRML (The Virtual Reality Modeling Language) 虚拟现实建模语言 API (application programmer interface) 应用程序界面 586
  • 587. 14.2 About VRML The Virtual Reality Modeling Language (VRML) is a file format for describing interactive 3D objects and worlds. VRML is designed to be used on the Internet, intranets, and local client systems. VRML is also intended to be a universal interchange format for integrated 3D graphics and multimedia. VRML may be used in a variety of application areas such as engineering and scientific visualization, multimedia presentations, entertainment and educational titles, web pages, and shared virtual worlds. 虚拟现实建模语言(VRML)是一种描述交互式三维对象及客观世界的文件格式。VRML用于Internet、Intranet和局域客户系统。VRML也是组合三维图形和多媒体的通用转换格式。VRML的应用领域很广,包括工程、科学可视化、多媒体演示、娱乐教育、Web页面和共享虚拟世界等方面。 587
  • 588. 14.2 About VRML 14.2.1 Design Criteria VRML has been designed to fulfill the following requirements: Authorability Enable the development of computer programs capable of creating, editing, and maintaining VRML files, as well as utomatic translation programs for converting other commonly used 3D file formats into VRML files. 14.2.1 设计标准 VRML需要满足如下要求: 创作性 使得应用程序能够建立、编辑、保存VRML文件,也是一个自动 翻译程序,能够将通常使用的3D文件格式转换成VRML文件。588
  • 589. 14.2 About VRML l        14.2.1 Design Criteria Composability Provide the ability to use and combine dynamic 3D objects within a VRML world and thus allow re-usability. l         Extensibility Provide the ability to add new object types not explicitly defined in VRML. 重构性 能够在VRML环境中使用和组合动态3D对象,并允许重用。 扩展性 能够加入在VRML中没有明确定义的新的对象类型。 589
  • 590. 14.2 About VRML l         14.2.1 Design Criteria Implementability Capable of implementation on a wide range of systems. Performance Emphasize scalable, interactive performance on a wide variety of computing platforms. l          Scalability Enable arbitrarily large dynamic 3D worlds. 适用性 能够在各种系统中使用。 性能 在各种不同的计算机平台上强调可扩展的、交互的性能。 可扩展性 适于任意大的动态三维世界。 590
  • 591. 14.2 About VRML l     14.2.2 Characteristics of VRML VRML is capable of representing static and animated dynamic 3D and multimedia objects with hyperlinks to other media such as text, sounds, movies, and images [1]. VRML browsers, as well as authoring tools for the creation of VRML files, are widely available for many different platforms. VRML的特性 VRML能表示静态及动态的三维和多媒体对象,并通过超链接连到诸如文本、声音、电影及图像等其它媒体。VRML浏览器,同制作VRML文件的制作工具一样,广泛应用于许多不同的平台上。591
  • 592. 14.2 About VRML l         14.2.2 Characteristics of VRML VRML supports an extensibility model that allows new dynamic 3D objects to be defined and a registration process that allows application communities to develop interoperable extensions to the base standard. There are mappings between VRML objects and commonly used 3D application programmer interface (API) features. VRML支持扩展模式,即允许创建新的3维动态对象,并允许应用程序组开发在基础模式上加以扩展的可共同操作的文件。在VRML对象和通常使用的应用程序接口特性间有相应的映射。592
  • 593. 14.2 About VRML l         14.2.3 Scope The VRML specification defines a file format that integrates 3D graphics and multimedia. Conceptually, each VRML file is a 3D time-based space [3] that contains graphic and aural objects that can be dynamically modified through a variety of mechanisms. VRML defines a primary set of objects and mechanisms that encourage composition, encapsulation, and extension. 领域 VRML规范定义了一种可将3D图形和多媒体结合起来的文件格式。总体上,每个VRML文件是3维时间依赖空间,包含能够通过不同机制动态修改的图像和音频对象。VRML定义了一个对象的初始集,并允许将对象进行合成、封装和扩充。593
  • 594. 一、产品广告的结构 (Elements of product advertisement) 一则广告一般包含如下内容: (1) 标题,用于阐述该产品名称和最显著、最重要的特点,有的还用小标题进一步说明。 (2) 产品样本照片或外形图、剖面图。这部分往往与标题相互配合,简短广告常省略此部分。 (3) 正文列举其主要品种、规格、性能、用途和特点。 (4) 商标、名称、代理机构、经销单位及地点、邮政编码、电话号码、用户电报、电报挂号及联系人等商业信息。广告文体简介594
  • 595. 二、广告语言的特点 (Characteristics of advertising language) 广告与其他科技文体有很大区别,它的语言不但精练,而且生动、活泼。它广泛采用了形象、拟人、典故、夸张等修辞手法和押韵、叠文、一语双关等文字技巧,以增强广告的渲染力。广告英语具有如下重要特色。 使用不同字体和图形,突出最重要的、最令人感兴趣的信息。这种手段简洁易懂,使人一目了然。如: (a) Finally, the dBASE, you’ve been waiting IV. Get the new dBASE IV, Now for just $ 449 “大家盼望已久的dBASE 增强型版本dBASE IV 终于问世了。该软件目前的售价仅为449美元。 (b) Twice the performance at half the cost. The New Ultra Graphics Accelerator from Metheus “花一半的钱,却得双倍的性能,何乐而不为!”这是Methus公司为其图形加速器所作的广告。广告文体简介595
  • 596. 二、广告语言的特点 (Characteristics of advertising language) (2) 别出心裁,用违反常规的说法,夸大其辞。如: Are you getting fat & lazy waiting for your plotter? Don’t wait! — Get PLUMP “绘图仪的速度实在太慢,使人等得又胖又懒,还是买PLUMP吧!”这是一家公司为推销其PLUMP产品而作的极为夸张的广告。 (3) 为使广告通俗易懂,常采用家喻户晓的口语和俗语等非正式文体,使公众感到亲切,便于记忆。如:Here’s proof that something small can be powerful.这条广告说明了某微型机“体积虽小,但功能强大”。 A whole year without a single bug! 这说明该公司的产品质量过硬,“整整一年没有出一次故障”。广告文体简介596
  • 597. 二、广告语言的特点 (Characteristics of advertising language) (4) 为吸引顾客,使语言生动活泼,常采用形象化、拟人化等手段。例如,有一幅画着驴的广告,上写: I feel like a donkey!For not buying the “Access” portable computer. 这是Access 为其便携式计算机做的广告,它给人一种幽默感、新鲜感。广告文体简介597
  • 598. 下面是一则广告,可从中体会广告文体的特点。 Over l00 MB Removable Drives Fight it Out: Magnetic vs Optical Storage systems with removable disks and capacities of 100 Mbytes or more are beginning to be mounted in personal computers. Within a few years floppy disks with capacities of over 100 Mbytes and optical disks with capacities of 650 Mbytes are expected to be standard storage devices. There types of high-density floppy disks have appeared in the US and Japan, with the Zip drive from Iomega Corp of the US leading in shipments. The LS-120 from Matsushita Industries, Ltd of Japan and the drive being developed by Mitsumi Electric Co, follow closely in second and third place. In optical disk drives, the CD-R drives are receiving high praise because it allows data to be read on a standard CD-ROM drive广告文体简介598
  • 599. Thank you!