Computer Overview

I. Introduction

    A computer is an electronic（adj.电子的） device that can receive a set of instructions, or program, and then carry out this program by performing calculations on numeric（adj.数字的） data or by manipulating（vt.操作，使用） 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 transaction to private household accounts. 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（n.&v.推测, 臆说, 猜想）database services and computer networks make available a great variety of information sources.  The same advanced techniques also make possible invasions of personal and business privacy Computer crime has become one of the many risks that are part of the price of modern technology.

II. History

   The first adding machine, a precursor （n.先驱）of the digital computer, was devised in 1642 by the French scientist, mathematician, and philosopher Blaise Pascal. This device employed a series of ten-toothed wheels, each tooth representing a digit from 0 to 9. The wheels were connected so that numbers could be added to each other by advancing the wheels by a correct number of teeth. In the 1670s the German philosopher and mathematician Gottfried Wilhelm Leibniz improved on this machine by devising one that could also multiply,                                               

    The French inventor Joseph-Marie Jacquard, in designing an automatic loom（n.织布机）, used thin, perforated wooden boards to control the weaving of complicated designs. During the 1880s the American statistician（n.统计员，统计学家） Herman Hollerith conceived （vt.构思）the idea of using perforated（adj.穿孔的, 凿孔的） cards, similar to Jacquard's boards, for processing data. Employing a system that passed punched cards over electrical contacts he was able to compile（vt.编译, 编辑, 汇编） statistical information for the 1890 United States census（n.人口普查）.

 l. The Analytical Engine

    Also in the 19th century, the British mathematician and inventor Charles Babbage worked out the principles of the modern digital computer. He conceived a number of machines, such as the difference engine that were designed to handle complicated mathematical problems. Many historians consider Babbage and his associate（n.合作人，同事）, the mathematician Augusta Ada Byron, the true pioneers of the modern digital computer. One of Babbage's designs, the Analytical Engine had many features of a modem computer. It had an input stream in the form of a deck of punched cards（穿空卡片）, a "store" for saving data, a "mill" for arithmetic operations, and a printer that made a permanent record, Babbage failed to put this idea into practice, though it may well have been technically possible at that date.

 2. Early Computers

    Analogue computers （模拟计算机）began to be built in the late 19th century. Early models calculated by means of rotating, shafts and gears（n.齿轮, 传动装置）. Numerical approximation of equations too difficult to solve in any other way were evaluated with such machines. Lord Kelvin built a mechanical tide predictor that was a specialized analogue computer. During World Wars I and II, mechanical and, later, electrical analogue computing systems were used as torpedo（n.×××, 油井爆破筒） course predictors in submarine and as bombsight controllers in aircraft. Another system was designed to predict spring floods in the Mississippi River basin（n.流域）.

 3. Electronic Computers

    During World War II, a team of scientists and mathematicians, working at

Bletchley

Park

, north of

London

, created one of the first all-electronic digital computers: Colossuss. By December 1943, Colossus, which incorporated 1500 vacuum（n.真空 ）tubes, was operational. It was used by the team headed by Alan Turing, in the largely successful attempt to crack German radio messages enciphered in the Enigma code.

    Independently of this, in the United States， a prototype electronic machine had been built as early as 1939， by John Atanasoff and Clifford Berry at Iowa State College. This prototype and later research were completed quietly and later overshadowed by the development of the Electronic Numerical integrator And Computer (ENIAC) in 1945. ENIAC was granted patent（adj.显著的） which was overturned decades later, in 1973, when the machine was revealed to have incorporated principles first used in the Atanasoff-Berry Computer.

    ENIAC contained 18,000 vacuum tubes and had a speed of several hundred multiplications per minute, but originally its program was wired into the processor and had to be manually altered.

    Later machines were built with program storage, based on the ideas of the Hungarian-American mathematician John von Neumann. The instructions, like the data, were stored within a "memory", freeing the computer from the speed limitations of the paper-type reader during execution and permitting problems to be solved without rewriting the computer.

    The use of the transistors（n.电子晶体管） in computers in the late 1950s marked the advent of smaller, faster, and more versatile（adj.通用的, 万能的, 多才多艺的, 多面手的） logical elements than were possible with vacuum-tube machines. Because transistors use much less power and have a much longer life, this development alone was responsible for the improved machines called second-generation computers Components became smaller, as did inter-component spacings, and the system became much less expensive to build.

4. Integrated Circuits

    Late in the 1960s the integrated circuit, or IC (See Figure IA-2), was introduced, making it possible for many transistors to be fabricated（vt.制作, 构成, 捏造, 伪造, 虚构） on one silicon substrate（硅片）, with interconnecting wires plated in place. The IC resulted in a further reduction in price, size, and failure rate. The microprocessor became a reality in the mid-1970s with the introduction of the large-scale integrated (LSD circuit and, later, the very large-scale integrated (VLSI) circuit (microchip), with many thousands of interconnected transistors etched into a single silicon substrate.

    To return, then, to the switching capabilities of a modern computer in the 1970s were generally able to handle eight switches at a time That is ,they could deal with 8 binary digits ,or bits of data ,at every cycle. A group of eight bits is called a byte, each byte containing 256 possible patterns of ONs and OFFs (or 1s and Os). Each pattern is the equivalent （n.等价物）of an instruction, a part of an instruction, or a particular type of datum, such as a number or a character or a graphics symbol. The pattern 11010010, for example, might be binary data--in this case, the decimal number 210--or it might be an instruction telling the computer to compare data stored in its switches to data stored in a certain memory-chip location.

    The development of processors that can handle 16, 32, and 64 bits of data at a time has increased the speed of computers. The complete collection of recognizable patterns---the total list of operations---of which a computer is capable, is called its instruction set. Both factors---the number of bits that can be handled at one time and the size of instruction sets--continue to increase with the ongoing development of modern digital computers.

III. Hardware

    Modern digital computers are all conceptually （adv.概念地）similar, regardless of size. Nevertheless, they can be divided into several categories on the basis of cost and performance: the personal computer or microcomputer, a relatively low-cost machine, usually of desktop size (though laptops are small enough to fit in a briefcase, and "palmtops" can fit into a pocket); the workstation, a microcomputer with enhanced graphics and communications capabilities that make it especially useful for office work; the minicomputer, generally too expensive for personal use, with capabilities suited to a business, school, or laboratory; and the mainframe computer, a large, expensive machine with the capability of serving the needs of major business enterprises, government departments, scientific research establishments, or the like (the largest and fastest of these are called supercomputers).

    A digital computer is not a single machine: rather, it is a system composed of five distinct（adj.清楚的, 明显的, 截然不同的, 独特的） elements: (1) a central processing unit; (2) input devices; (3) memory storage devices; (4) output devices; and (5) a communications network, called a bus, which links all the elements of the system and connects the system to the external world.

IV. Programming

    A program is a sequence （n.次序, 顺序, 序列）of instructions that tells the hardware of a computer what operations to perform on data. Programs can be built into the hardware itself, or they may exist independently in a form known as software. In some specialized, or dedicated computers the operating instructions are embedded in their circuitry; common examples are microcomputers found in calculators, wristwatches（n..手表）, car engines and microwave ovens. A general-purpose computer, on the other hand, although it contains some built-in programs (in ROM) or instructions (in the processor chip), depends on external program to perform useful tasks. Once a computer has been programmed, it can do only as much or as little as the software controlling it at any given moment enables it to do. Software in widespread use includes a wide range of applications Programs-instructions to the computer on how to perform various tasks.  

V. Future Developments

    One continuing trend in Computer development is microminiaturization（n. 微小型化） the effort to compress more circuit elements into smaller and smaller chip space. Researchers are also trying to speed up circuitry（n. 电路, 线路） functions through the use of superconductivity（n. [物]超导电性）, the phenomenon of decreased electrical（adj.电的, 有关电的) resistance observed in certain materials at very low temperatures.                                                                

    The "fifth-generation" computer effort to develop computers that can solve complex problems in ways that might eventually（adv.最后, 终于） merit（v.有益于）the description "creative'' is another trend in computer development, the ideal goal being true artificial intelligence One path actively being  explored is parallel-processing computing, which uses many chips to perform several different tasks at the same time. One important parallel-processing approach is the neural（adj.神经系统的, 神经中枢的, 背的） network which mimics the architecture of the nervous system. Another ongoing trend is the increase in computer networking which now employs the worldwide data communications system of satellite and cable links to connect computers globally. There is also a great deal of research into the possibility of "optical"（adj.眼的, 视力的, 光学的） computers----hardware that processes not pulses（n.脉搏, 脉冲) of electricity but much faster pulses of light.