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Computer and Its Kind
计算机及其种类
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.
The modern world of high technology could not have come about except for the development of the computer. Different types and sizes of computers find uses throughout society in the storage and handling of data, from secret governmental files to banking transactions to private household accounts^[1]. Computers have opened up a new era in manufacturing through the techniques of automation, and they have enhanced modern communication systems. They are essential tools in almost every field of research and applied technology, from constructing models of the universe to producing tomorrow's weather reports, and their use has in itself opened up new areas of conjecture. Database services and computer networks make available a great variety of information sources^[2]. The same advanced techniques also make the invasions of privacy and restricted information sources possible, and computer crime has become one of the many risks that society must face if it is to enjoy the benefits of modern technology.
Types of Computers
1. Microcomputer
A microcomputer is a desktop or notebook size computing device that uses a microprocessor as its Central Processing Unit, or CPU. Microcomputers are also called Personal Computers (PCs) , home computers, small business computers, and micros. The smallest, most compact are called laptops. When they first appeared, they were considered single user devices, and they were capable of handling only 4, 8, or 16 bits of information at one time. More recently the distinction between microcomputers and large, mainframe computers as well as the smaller mainframe type systems called minicomputers has become blurred, as newer microcomputer models have increased the speed and data handling capabilities of their CPUs into the 256 bit, or even much more bit multiuser range.
Microcomputers are designed for use in homes, schools, and office settings. Within the home, they can serve both as a tool for home management balancing the family checkbook, structuring the family budget, indexing recipes and as a recreational device playing computer games, cataloging records and books. School children can use microcomputers for doing their homework, and in fact many public schools now employ the devices for programmed learning and computer literacy^[3]courses. Small businesses may purchase microcomputers for word processing, bookkeeping, the storage and handling of mailing lists and so on.
Desktop Computer
A desktop computer is a personal computer in a form intended for regular use at a single location, as opposed to a mobile laptop or portable computer. Prior to the wide spread of microprocessors a computer that could fit on a desk was considered remarkably small. Today the phrase usually indicates a particular style of computer case. Desktop computers come in a variety of styles ranging from large vertical tower cases to small form factor models that can be tucked behind an LCD^[4]monitor. In this sense the term "desktop" refers specifically to a horizontally-oriented case, usually intended to have the display screen placed on top to save space on the desk top. Most modern desktop computers have separate screens and keyboards. A specialized form of desktop case is used for home theater PC systems, incorporating front-panel mounted controls for audio and video.
Personal Digital Assistant (PDA)^[5]
A personal digital assistant (PDA) is a handheld computer, also known as a palmtop computer. Newer PDAs also have both color screens and audio capabilities, enabling them to be used as mobile phones, smartphones, web browsers, or portable media players. Many PDAs can access the Internet, intranets or extranets via Wi-Fi^[6], or Wireless Wide-Area Networks (WWANs^[7]). Many PDAs employ touch screen technology.
Tabjet^[8]PC
A Tablet PC is a laptop mobile computer, equipped with a touchscreen or graphics tablet/screen hybrid technology which allows the user to operate the computer with a stylus or digital pen, or a fingertip, instead of a keyboard or mouse. This form factor offers a more mobile way to interact with a computer. Tablet PCs are often used where normal notebooks are impractical or unwieldy, or do not provide the needed functionality.
Laptop^[9]
A laptop (also known as a notebook) is a personal computer designed for mobile use small enough to sit on one's lap. A laptop includes most of the typical components of a typical desktop computer, including a display, a keyboard, a pointing device, a touchpad, also known as a trackpad, or a pointing stick, as well as a battery, into a single small and light unit. The rechargeable battery required is charged from an AC/DC adapter and typically stores enough energy to run the laptop for several hours.
2. Minicomputer
A minicomputer is a mid-level computer built to perform complex computations while dealing efficiently with a high level of input and output from users connected via terminals. Minicomputers also frequently connect to other minicomputers on a network and distribute processing among all the attached machines. Minicomputers are used heavily in transaction processing applications and as interfaces between mainframe computer systems and wide area networks.
3. Mainframe Computer
A mainframe computer is a high level computer designed for the most intensive computational tasks. Mainframe computers are often shared by multiple users connected to the computer via terminals. The most powerful mainframes, called supercomputers, perform highly complex and time-consuming computations and are used heavily in both pure and applied research by scientists, large businesses, and the military.
4. Others
·Servers
A server usually refers to a computer that is dedicated to providing a service. For example, a computer dedicated to a database may be called a "database server". "File servers" manage a large collection of computer files. "Web servers" process web pages and web applications. Many smaller servers are actually personal computers that have been dedicated to providing services for other computers.
A server is a computer program that provides services to other computer programs and their users in the same or other computer. The physical computer that runs a server program is also often referred to as server.
Services can be supplied centrally by the use of a server; in other cases all the machines on a network have the same status with no dedicated server, and services are supplied peer-to-peer^[10].
·Workstation
Workstations are computers that are intended to serve one user and may contain special hardware enhancements not found on a personal computer.
It is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems. The term workstation has also been used to refer to a mainframe computer terminal or a PC connected up to a network.
Historically, workstations had offered higher performance than personal computers, especially with respect to graphics and CPU power, memory capacity and multitasking ability. They are optimized for display and manipulation of different types of complex data such as 3D mechanical design, engineering simulation (e. g. computational fluid dynamics), animation and rendering of images, and mathematical plots. Consoles consist of a high resolution display, a keyboard and a mouse at a minimum, but also offer multiple displays, graphics tablets, SpaceBalls, etc. Workstations are the first segment of the computer market to present advanced accessories and collaboration tools.
·Embedded computers
Embedded computers are computers that are a part of a machine or device. Embedded computers generally execute a program that is stored in non-volatile memory and is only intended to operate a specific machine or device. Embedded computers are very common. Embedded computers are typically required to operate continuously without being reset or rebooted, and once employed in their task the software usually cannot be modified. An automobile may contain a number of embedded computers; however, a washing machine and a DVD player would contain only one. The central processing units (CPUs) used in embedded computers are often sufficient only for the computational requirements of the specific application and may be slower and less expensive than CPUs found in personal computers.
·Supercomputer
In computer science, supercomputers are large, extremely fast, and expensive computers used for complex or sophisticated calculations, typically, machines capable of pipelining instruction execution and providing vector instructions. A supercomputer can, for example, perform the enormous number of calculations required to draw and animate a moving spaceship in a motion picture^[11]. Supercomputers are also used for weather forecasting, large scale scientific modeling, oil exploration and so on and so like.
Future Developments
One ongoing trend in computer development is microminiaturization, the effort to compress more circuit elements into smaller and smaller chip space. Researchers are also trying to speed up circuitry functions through the use of superconductivity, the phenomenon of decreased electrical resistance observed as objects exposed to very low temperatures become increasingly colder^[12]. The fifth-generation computer, the effort to develop computers that can solve complex problems in what might eventually be called creative ways, is another trend in computer development, the ideal goal being true artificial intelligence^[13].
Quantum Computer
A quantum computer^[14], quite different from classical current computers, is a device that harnesses physical phenomenon unique to quantum mechanics to realize a fundamentally new mode of information processing. In a quantum computer, the fundamental unit of information called a quantum bit (or qubit), is not binary but rather more quaternary in nature. A qubit can exist not only in a state corresponding to the logical state 0 or 1 as in a classical bit, but also in states corresponding to a blend or superposition of these classical states. In other words, a qubit can exist as a 0, a 1, or simultaneously as both 0 and 1, with a numerical coefficient representing the probability for each state.
DNA Computer
DNA computing^[15]is a form of computing which uses DNA, biochemistry and molecular biology, instead of the traditional silicon-based computer technologies. DNA computing, or. more generally, molecular computing, is a fast developing interdisciplinary area and is fundamentally similar to parallel computing in that it takes advantage of the many different molecules of DNA to try many different possibilities at once. And DNA computers are faster and smaller than any other computer built so far.
Optical Computer^[16]
An optical computer is a computer that uses light instead of electricity (i. e.photonsrather thanelectrons) to manipulate, store and transmit data. Optical computer technology is still in the early stages: functional optical computers have been built in the laboratory, but none have progressed past the prototype stage.
Molecule Computer
A molecular computer that uses enzymes to perform calculations has been built and it is believed enzyme-powered computers could eventually be implanted into the human body and used to, for example, tailor the release of drugs to a specific person's metabolism.
It used two enzymes to trigger two interconnected chemical reactions. Two chemical components-hydrogen peroxide^[17]and glucose^[18]-were used to represent input values A and B. The presence of each chemical corresponded to a binary 1, while the absence represented a binary 0. The chemical result of the enzyme-powered reaction was determined optically.
Notes
[1]... from secret governmental files to banking transactions to private household accounts.
①from... to:从……到。
②banking transactions to：对……的金融交易此处指银行转账，大意为：从政府的秘密文件到银行对私人家庭账户的账目往来。
[2]... make available a great variety of information sources. 本句和下一句均为倒装句，在宾语过长而其补语太短的情况下，常使用这一结构。原结构应为“to make sth. available/possible”。
[3]computer literacy计算机扫盲。“literacy”，原意为“识字，扫盲，有读和写的能力”，这里引申为“使用计算机的基本能力”。
[4]LCD (liquid crystal display)液晶显示，通过将具有极性分子结构的液体混合物夹在两个透明的电极间构成的显示方式。
[5]Personal Digital Assistant (PDA)个人数字助理。它是一种轻便的掌上型计算机，既有通信功能，又有个人组织功能，包括日历、笔记、数据库、计算器等。
[6]Wi-Fi (Wireless Fidelity)无线保真，是一种可以将个人电脑、手持设备，如PDA、手机等终端以无线方式互相连接的技术。Wi-Fi一词由Wi-Fi产业联盟(Wi-Fi Alliance)提出。
[7] WWAN (Wireless Wide-Area Networks)无线广域网，WWAN技术是使得笔记本电脑或者其他的设备装置在蜂窝网络覆盖范围内可以在任何地方连接到互联网，其下载速度可以与DSL相媲美。
[8]tablet图形输入板，在工程、设计和解释类的应用程序中用于输入图形位置信息的设备。
[9]laptop便携式计算机，一种为便于旅行时使用而设计的小型手提式计算机，可用电池或交流电源供电。
[10]peer-to-peer (P2P.)点对点技术，又称对等互联网络技术，是一种网络新技术，依赖网络中参与者的计算能力和带宽，而不是把依赖都聚集在较少的几台服务器上。P2P网络通常用于通过Ad Hoc连接来连接节点，也被使用在类似VoIP等实时媒体业务的数据通信中。纯点对点网络没有客户端或服务器的概念，只有平等的同级节点，同时对网络上的其他节点充当客户端和服务器。也有些专家称P2P是点对点技术，但其实是错的，实应解作群对群(Peer-to-Peer)。在虚拟私人网络VPN(Virtual Private Network)中，也有P2P这个名称，它才应解作点对点(Point-to-Point)。
[11]motion picture电影。
[12]..., the phenomenon of decreased electrical resistance observed as objects exposed to very low temperatures become increasingly colder. 此处，过去分词“observed”用作定语，修饰名词“the phenomenon”，它所带的状语从句中的过去分词短语“exposed to”修饰名词“objects”。可以翻译成“当暴露于超低温的物体的温度越来越低时，即可观察到电阻值降低的现象”。
[13]...，the ideal goal being true artificial intelligence. 分词独立结构，句中起说明作用，可翻译成“理想的目标是真正的人工智能”。
[14]quantum computer量子计算机，由理查德·费曼提出，是从物理现象的模拟而来的。量子电脑能做出对数运算，而且速度远胜传统电脑。这是因为量子不像半导体只能记录0与1，可以同时表示多种状态，一个40位元的量子电脑，就能解开1024位元电脑花上数十年解决的问题。
[15]DNA computing，DNA运算，或译DNA计算，是一种电脑运算形式，利用DNA、生物化学以及分子生物学原理，而非传统上以硅为基础的电脑技术。
[16]optical computer光学计算机，利用可见光或红外光而不是电流进行数据处理，从全息存储、激光存储或存储库输入数据的计算器，多用于指纹鉴定和图像清晰化的处理过程。
[17]hydrogen peroxide过氧化氢：一种无色、重、具有很强氧化作用的液体H₂O₂。
[18]glucose葡萄糖：一种单糖，C₆H₁₂O₆，广见于大多数动植物组织。

Computer Systems Architecture^[1]
计算机系统结构
1. Computer systems-the importance of networking
Since there is not yet a universal definition of Computer Systems Architecture (CSA), interpretations vary. Student confusion increases because commercial terminology can be even more creative! Sometimes CSA appears in the hardware orientation of digital electronics; at other times it takes on the guise of a unified software specification for a family of computers. Rarely is the central importance of network facilities,^[2]both to the computer designer and to the end user, sufficiently acknowledged, even though we are all aware of its growing significance in society. Indeed, more and more computer science graduates become involved in the data communications industry, and would therefore benefit from grounding in this field. Thus an aim of this text is to place networks solidly within CSA.^[3]
It is clear that computers and networks require both hardware and software in order to work. But the historical academic separation of the two poses a difficult balancing problem when presenting such a course.^[4]Both are equally important and strongly connected by their enthusiastic supporters. The distinction between hardware and software can be likened to the distant relationship between the formal team player, rigidly posed in front of the goalmouth, and the exciting unpredictability of the World Cup final.^[5]The static photograph of the players only vaguely hints at the limitless possibilities of the dynamic game. With the increasing sophistication of computer hardware, perhaps it is unfortunate that the taking-apart and exploration of old computers is no longer encouraged. The unexpectedly rising prices of electronic components, added to the need to have modern equipment to run the latest games, have resulted, for the moment, in a salesperson's dream. Unexpectedly, this trend, although attracting many more people to use computers, has had an adverse effect on the fundamental level of knowledge among computing undergraduates on entry to university. Although we cannot turn the clock back to the self- build hobbyist days of home computing,^[6]knowledge of the interaction of hardware and software is still useful, if not necessary, for anyone wanting to be fully involved in the professional use of computers.
Curiosity about the computer systems which surround us, the Internet that frustrates us, and the mobile telephone networks that we increasingly rely on should drive us to investigate and question what is happening in the fields of software and electronics. The facilities that will become available to us in the next few years will depend largely on current developments in microelectronics and software design methodology. It is here that we can look for the future.
Throughout this passage we will treat CSA as a study of the interaction of hardware and software which determines the performance of network computer systems. We will also try to show that computers can always be viewed as hierarchical ordered systems which can be broken down into simpler component parts in order to fully understand their operation.^[7]Unlike other areas of study, such as physics or chemistry, complex ideas can always be split into simpler concepts which may then be understood more easily. This progressive decomposition approach not only is useful when studying computers, but can also be invaluable when designing and building new systems.^[8]
2. Hardware and software-mutual dependence
Although it is widely recognized that computer systems involve both hardware and software, it is still rare for college computer courses to require you to have a comparable understanding in both fields. Perhaps the analogy of only eating half a boiled egg is appropriate-you risk missing out on the yolk. This separation, or specialization, has a number of serious negative results. When teams of developers are separately recruited as hardware engineers or programmers, the danger of an opposing split progressively opening up between the two camps is always present. Professional rivalry can arise through simple misunderstandings due to the different approaches and vocabulary used by hardware and software engineers. Problems, when they inevitably occur, can be blamed on the other camp and then take longer to resolve. Programmers sometimes find that unsuitable equipment has already been specified without consultation, and hardware designers can sit helplessly by as unsuitable software fails to exploit the performance advantages offered by their revolutionary new circuits.
It has been claimed by some business analysts that hardware manufacturing will be of no great commercial consequence. The profit lies in programming: lead the world in the development of systems software! But it is now clear that in such a rapidly changing world, early access to new hardware designs gives the software industry an important marketing lead. The first software products to exploit some new hardware faculty have a clear leadership in the market-place. The neglect of the hardware side of the computing industry has never delivered any long-term advantage. Understanding basic principles and appreciating their application by modem technology within a range of current products is a central aim of this text. Programmers neglect developments in hardware at their peril. The opposite situation, where software is overlooked, can lead to similar failures. Consider the much greater commercial success of the PC since running the Windows operating system and the recent explosion in use of the Internet. Many excellent machines became commercial failures because of their sub-standard software. These well-rehearsed public examples can be added to and confirmed by thousands of private disasters which all underline the need to pursue hardware and software developments in concert. We now recognize that despite their technical superiority, computer systems can fail to win acceptance for many reasons, such as a poorly thought-out user interface, a lack of applications s.oftware, or an inappropriate choice of operating system.^[9]Many recent developments have arisen from a simultaneous advance in hardware and software: windowing interfaces are only possible through sophisticated software and powerful graphics cards; network connections are supported by autonomous coprocessors working with complex driver routines; laser printers became universally popular when the xerography print engine was supplemented by the PostScript interpreter.^[10]Many such examples demonstrate the value of keeping abreast of developments in both hardware and software. An increasing difficulty with investigating the interaction of hardware and software i.s gaining access to the relevant facilities. With large, multi-user mainframe computers it was understandable that the ordinary programmer was denied^[11]access to the hardware and critical software to protect other users. However, with the introduction of Windows NT such security constraints were introduced to single-user personal workstations, making it impossible to access the hardware directly. Only the operating system code has this privilege, while ordinary programs are forced to call "trusted" system routines to read or write to any part of the hardware.
3. Programming your way into hardware
A remarkable empirical law describing the rapid growth of silicon technology was proposed by Gordon Moore, one of the founders of Intel.^[12]His well-known rule, Moore's Law, states that the amount of circuitry (number of transistors) which can be placed on a given chip area approximately doubles every two years. A circuit designed 24 months ago can now be shrunk to fit into an area of half the size. Intel's original 4004 processor involved 2300 transistors, while the Pentium 4 has somewhere of the order of 42 million. The chip area had not increased by a factor of 2000! This capability to progressively shrink the size of electronic circuits could reduce the chip cost, because more circuits are processed on a single slice of silicon, but the technical advance has more often been exploited by enhancing the chip ' s functionality.
Surprisingly, this law has held true since the early 1970s and is likely to stand well into the 2020s before the size of circuit elements become so small that quantum physics intervenes through Heisenberg' s uncertainty principle.^[13]Already the on-chip circuit interconnections are only 0.25 um long and the insulating layers can be as thin as a couple of dozen molecules. However, Moore's Law remains somewhat of a mystery, given that the underlying variables responsible for the trend are as diverse as the ability to maintain ultra-clean factory environments, reduction of international trade barriers, development of increasingly high-resolution technology and the marketing success of games consoles!
Although the split between those concerned with hardware and those concerned with software is now deeply rooted, there are developments which might reverse this trend. As manufacturing techniques allow components to shrink in size, hardware engineers find it increasingly difficult to wire up "breadboard" prototypes because the circuits they are building have grown too complicated.^[14]In any case. the performance of the large-sized components which they can handle easily in a traditional way is not identical to that of the miniature equivalents which will make up the final integrated circuit that is produced.
In the past there was a tendency for trained electronic engineers to migrate towards software, to pick up programming skills and to get involved in systems programming. Will this trend now be reversed？ Programmers, software engineers, trained to deal with large systems and complex specifications, may take the opportunity of contributing to the hardware design. This is another example of how hardware and software can come together through the tools and skills demanded by systems developers.
Notes
[1]Computer Systems Architecture (CSA)计算机系统结构。计算机系统结构是从外部来研究计算机系统的一门学科，一般说来，凡是计算机系统的使用者(包括一般用户和系统程序员)所能看到的计算机系统的属性都是计算机系统结构所要研究的对象。
[2]Rarely is the central importance of network facilities……计算机设计者和终端用户很少能认识到网络设备的重要性。否定副词rarely放在句首表示强调，句子要倒装。例如：Rarely can he finish his work in time. 他很少按时完成作业。
[3]Thus an aim of this text is to place networks solidly within CSA. 因此，本文旨在于计算机系统结构中打下坚实的基础。
[4]But the historical academic separation of the two poses a difficult balancing problem when presenting such a course. 由于历史上两者的教学相互分离，开设这门课程，就出现了怎么样兼顾的问题。
[5]The distinction between hardware and software can be likened to the distant relationship between the formal team player, rigidly posed in front of the goalmouth, and the exciting unpredictability of the World Cup final．计算机硬件与软件的区别，正如足球场上生硬地点在球门前准备射门的球员，与世界杯决赛的结果，扑朔迷离，难以预测。
[6]Although we cannot turn the clock back to the self-build hobbyist days of home computing……虽然我们不能使时光倒流到自己组装家用电脑的年代……
[7]We will also try to show that computers can always be viewed as hierarchical ordered systems which can be broken down into simpler component parts in order to fully understand their operation. 我们试图说明计算机是一个分级有序的系统，可以分解成更简单的组成部分，这样的话我们就可以更好地了解他们是如何运行的。
[8]This progressive decomposition approach……这种循序渐进的分解方法
[9]...such as a poorly thought-out user interface……例如一个缺乏深思熟虑的用户界面
[10]...the PostScript interpreter... PostScript解码器……。PostScript是由Adobe公司所开发的页面描述语言，是一种桌面系统向输出设备输出的界面语言，专门为描述图像及文字而设计。PostScript是国际是最流行的页面描述语言，其最大特点是能够综合处理文字和图形、图像，也是事实上的工业标准。几乎所有的印前输出设备都支持PS语言，PS语言的成功也使开放式的电子出版系统在国际上广泛流行。
[11]was denied access to the hardware……被拒绝使用硬件
[12]Gordon Moore戈登·摩尔。1929年出生在美国加州，并在加州理工大学(CIT)获得物理和化学两个博士学位。1950s中期他和集成电路的发明者罗伯特·诺伊斯(Robert Noyce)一起，在威廉·肖克利半导体公司工作。后来，诺伊斯和摩尔等8人集体辞职创办了半导体工业史上有名的仙童半导体公司(Fairchild Semiconductor)。仙童成为现在的Intel和AMD之父。1968年，摩尔和诺伊斯一起退出仙童公司，创办了Intel。摩尔定律是指IC上可容纳的晶体管数目，约每隔18个月便会增加一倍，性能也将提升一倍。
[13]Heisenberg's uncertainty principle. 海森堡测不准原理，又名“测不准原理”、“不确定关系”。该原理表明：一个微观粒子的某些物理量(如位置和动量，或方位角与动量矩，还有时间和能量等)，不可能同时具有确定的数值，其中一个量越确定，另一个量的不确定程度就越大。测量一对共轭量的误差的乘积必然大于常数h/2π(h是普朗克常数)是海森伯在1927年首先提出的，它反映了微观粒子运动的基本规律，是物理学中又一条重要原理。
[14]...wire up "breadboard" prototypes……为电路实验板原型接通电源