Passage Three The Advancement of the Computer
Training target: In this part ， you should try your best to form good reading habits. In order to avoid your ill habits such as regression ， you should read with the card showed to you in the preface of this book. Keep reading the paragraphs from the beginning to the end without stopping.
Text. The use of the transistor in computers in the late1950s marked the coming of the second-generation computers. The most notable change was that transistors replaced vacuum tubes. This meant that the advent of smaller ， faster ， more reliable and less expensive computers was possible with transistor machines. In addition ， the second-generation computers were given auxiliary storage ， sometimes called external or secondary storage. Data were stored outside the computer on either magnetic tapes or magnetic disks. Using magnetic tapes or magnetic disks for input and output operations increased the speed of the computer.
RAM capacities increased from 8 ， 000 to 64 ， 000words in commercially available machines by the1960s ， with access time of 2 to 3 ms （ milliseconds ）.These machines were very expensive to purchase or even to rent and were particularly expensive to operate because of the cost of expanding programming. Such computers were mostly found in large computer centers operated by industries ， governments and private laboratories—staffed with many programmers and support personnel.
Late in the1960s the integrated circuit ， or IC ， was introduced ， making it possible for many transistors to be included on one silicon chip. Therefore ， the computers became even smaller and cheaper while their memory capacities became larger. The microprocessor became a reality in the midˉ1970s with the largeˉscale integrated （ LSI ） circuit. The earliest microcomputer ， the Altair8800 ， was developed in1975by Ed Roberts; This machine used the Intel microprocessor and had less than1kilobyte of memory.
In the1980s ， very largeˉscale integrated （ VLSI ） circuits ， in which hundreds of thousands of electronic components were etched into a single silicon chip ， became more and more common. Many companies ， some new to the computer field ， introduced in the1970s programmable mini-computers supplied with software packages. The“shrinking”trend continued with the introduction of personal computers （ PCs ）， which are programmable machines small enough and inexpensive enough to be purchased and used by individuals.
By the late1980s ， some personal computers were run by microprocessors that ， handling32bits of data at a time ， could process about4 ， 000 ， 000instructions per second. Microprocessors equipped with read-only memory （ ROM ）， which storage constantly used ， unchanging programs ， now performed an increasing number of process-control ， testing ， monitoring ， and diagnosing functions ， like automobile ignition systems ， automobile- engine diagnosis and production-line inspection duties.
From the integrated circuit to large-scale integration and to very large-scale integration ， this was the start of the microprocessor age. The microprocessor continued to improve from the 8086 ， to the ， then Pentium ， Pentium Ⅱ and so on （ equivalent to and ）.
Modern digital computers are all conceptually similar ， regardless of the size. They can be divided into several categories on the basis of cost and performance: the personal computer or microcomputer ， a relatively lowˉcost machine ， usually of desktop size.
It also includes laptops which are small enough to fit in a briefcase and palmtops which 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 ， suitable for businesses ， schools ， or laboratories; the mainframe computer ， a large ， expensive machine which meets the needs of major business enterprises ， government departments ， scientific research establishments; the super-computer ， the largest and fastest computer.
A program is a sequence 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 circuitries; common examples are the microcomputers found in calculators ， wristwatches ， car engines ， and microwave ovens. Software in widespread use includes a wide range of application programs-instructions to the computer on how to perform various tasks.
Process in the area of software has not matched the great advance in hardware. Software has become the major cost of many systems because programming productivity has not increased very quickly. New programming techniques ， such as object-oriented programming ， have been developed to help relieve this problem. Despite difficulties with software ， however ， the cost per calculation of computers is rapidly lessening ， and their convenience and efficiency are expected to increase in the near future.
OOOOne continuing trend in computer development is microminiaturization，the effort to compress more circuit elements into smaller and smaller chip space.
The “fifth-generation” computer is using new technologies in very large integration ， along with new programming language ， and will be capable of amazing feats in the area of artificial intelligence ， such as voice recognition. One important parallel-processing approach is neural network ， which mimics the architecture of the nervous system. Another ongoing trend is the increase in computer networking ， electronic mail ， and electronic publishing. Advances in technologies continue to produce cheaper and more powerful computers.