History of Computers
The first general-purpose electronic computer to operate successfully was the Electronic Numerical Integrator and Computer (ENIAC)．Its construction was proposed in 1942 by John Mushily and J.Presser Eckert of the Moore School of Engineering, University of Pennsylvania. Work started on its development in June 1943 and the computer was completed by late 1945.It occupied 1500 ft2（140M2） of floor space, weighed over 30 tons, consisted of approximately 18000 vacuum tubes, 70000 resistors，10000 capacitors and 6000 switches and consumed150 kW of power. It was used to generate ballistic tables and weather forecasts．In principle it was programmable but this could only be done with consider--able difficulty by rewiring parts of the machine.
With the development of the ENIAC, the computer became a useful scientific and business tool The ENIAC could operate without human intervention, depending only upon stored instructions．This development marked the beginning of the modern computer era. Since then, many refinements in computers speed, size, and cost have been made．Many advancements in computer technology are divided into four time periods called generations．
1 ．First Generation of Computers
The first generation of computers lasted from•1951 to 1958. They were large, costly to buy, expensive to power, and often unreliable. Their internal operations were controlled through the use of vacuum tubes．These tubes were fairly large, and they generated so much heat that special air-conditioning had to be installed to handle it.
It was during this period that symbolic languages were developed. Symbolic languages use symbols made up of letters and numbers to stand for Os and 1 soft machine language. For example, ADD may stand for addition. Computer instructions written in symbolic languages were easier for people to use than machine language but symbolic language had to be translated into machine code before the computer could follow the instructions. The machine codes we restored on the outer surface of ma.netic drum.
2. Second Generation of Computers
The second generation of computers spanned the years from 1959 to 1964.It was during this time that the technology race really began．
The most notable change was that transistors replaced vacuum tubes．As a result, computers be-came much smaller，faster，and more reliable. They also became more efficient. Also at this time, magnetic cores replaced magnetic drums as storage media.
Next, the second generation of computers were given auxiliary storage, sometimes called external or secondary storage．Data was stored outside the computer on either magnetic tapes or magnetic disks．The use of auxiliary storage ended the limitation on how much data the computer could store and reduce these of punched cards．Using magnetic tapes for input and output operations increased the speed of computer.
Finally, improvements were made in the symbolic programming languages．New languages were more like English than the earlier ones, making progranuning the computer much easier.
3. Third Generation of Computers
The third generation of computers lasted from1965 to 1970 During the time, technology continued to improve and computers became even smaller, while their memory capacities became larger.
The third generation is marked chiefly by the development of integrated circuits，which replaced transistors．With integrated circuits，hundreds of electrum components could be included on one silicon chip less than one-eighth-inch square. A number of other developments characterized this period. For example, minicomputers were introduced．These machines had many of the same capabilities as large computers：but they were much smaller, had less storage space, and cost less．Another development was the use of remote terminals; in-put/output devices that are electronically linked to the main computer but located at some distance from it. A popular innovation was the introduction of families of computers that could support as many as forty different external devices，such as printer and remote terminals．Each computer in the family contained a different main storage capacity. A company could easily move up a machine with more storage while continuing to use the same external devices．
4 ．Fourth Generation of Computers
The period for the fourth generation of computers is given as 1971 to the present. Chip circuit has become increasingly miniaturized in the fourth generation of computers．Large-scale Integration (LSI)circuit, featuring thousands of electronic components on a single silicon chip became common during the1970s．From LSI technology came the microcomputer, the small "computer on a chip". Microprocessor chips can manage the functions of the computer, perform calculations, and control other devices just as large computers can. The combination of the microprocessor and other densely packed chips used for storage and input/output operations forms a microcomputer．Modern microcomputers have more power than the large computers of earlier generations．LSI has al-ready progressed into VLSI (Very Large Scale Integration), which means even more capabilities in even smaller packages．
翻译：
计算机的历史
第一台成功运行的通用电子计算机是ENIAC电子数值积分计算机）亡的结构是宾夕法尼亚大学牧尔工程学院的约翰，莫奇菜（John MaUChIN）与埃克特（J. PresperEckert ）于1942年提出的。该工程于1943年6月万始研制。它占地1500平方英尺（140M2），重量超过30吨。它由约18000只真空管，70000只电阻，10000只电容及6000只开关组成，耗电150KW o被用于编制弹道表及天气预报。从原理说，它是可编程的，但是。要做到这一点相当困难，因为要对机器的部件重新接线。
随着ENIAC的开发，计算机成为有用的科学和商业工具。ENIAC能够不需要人的干预而只依靠存储的指令进行操作。这个发展标志着现代化计算机时代的开端。从那以后，进行了许多对计算机在速度、大小、价格等方面的改进，被分为四个阶段，称为“代”。
1.第一代计算机
第一代计算机从1951年持续至1958年。’言们体积大，价格昂贵，启动费力且常常不可靠。它们的内部操作是通过真空管来控叙的。这些真空管很大，并且它们聚集了如此多的热量以至于不得不靠安装专门的空调来进行处理。 正是是这个时期，符号语言得到了开发。符号语言是用字母和数字组成的符号来代表机器语言的0和1。例如，ADD代表加法，用符号语言写的计算机指令比用机器语言写的指令对人来说要好用一些。但在计算机能执行这些指令之前，符号语言必须被翻译成机器代码，机器代码被存储在磁鼓的外表面。
2.第二代计算机
第二代计算机跨越了1959年，直到1964年。正是在这段时间里，技术竞争真正开始了。
最显著的变化是晶体管代替了真空管，它导致计算机的体积变得更小，更快，更可靠。同时也变得更高效了。也就是在这个时期，磁芯代替了磁鼓作为存储媒介。
其次，第二代计算机有了辅助存储器（有时一也称为外存或二级存储器）。数据被存储在计算机外部的磁带或磁盘上。辅助存储器的使用结束了计算机主存容量对程序和数据的规模的限制，减少了穿孔纸带的使用，采用磁带来进行输入与输出，提高了计算机的速度。
最后，在符号程序设计语言上也得到了改善。新的语言比以前更加接近英语，从而，为计算机设计程序变得更加容易了。
3.第三代计算机
第三代计算机从1965年持续至1970年。在此期间，技术继续得到了提高，同时计算机的体积变得更小，而其存储能力却更大了。
第三代计算机的主要标志是集成电路的发展，集成电路代替了晶体管。有了集成电路，成百上千的电子元件可以被集成到一块不到l／8平方英寸的硅片上。
另一些发展也成为这个时期的特色，例如产生了小型计算机。这些机器有许多大型机相同的能力。但它体积更小，存储容量更大而且更便宜。另一个发展是使用远程终端，即是一个远离主机但通过电子线路与主机联系在一起的输入输出设备。一个很受欢迎的改进是产生了能够支持多达40多个不同外部设备（这些设备的例子是打印机和远程终端等）的计算机系列中的每一种计算机都有不同的主存容量。计算机公司能够在使用原有的外部设备的情况下，通过增加存储容量轻易地将计算机升级。
4．第四代计算机
第四代计算机所处的阶段是1971年至今。第四代计算机的芯片电路已日益缩小化。70年代，以在单个硅片上集成成千上万电子元件为特色的大规模集成电路己变得很普及了。由于大规模集成技术而产生了微处理机，即“在一块芯片上的小型计算机”。微处理机芯片能管理计算机的功能，执行运算，控制其它设备，像大型机那样。微处理机和其它的用于存储和输入输出操作的紧密结合在一起的部件组合而产生了微机。现代的微机比早期的微机具有更强的能力。大规模集成电路己发展成为超大规模集成电路，这意味着更小的组件具有更大的能力。
文章来源于领测软件测试网 https://www.ltesting.net/
