个人计算机相关知识

Personal computerWhat is personal computer There have been many kinds of computer systems according to their size,such as su-percomputers,mainframe computers ,minicomputers and personal computers.Superco-mputers are special,high capacity computers used by very large organization principally for research purposes ,among which are oil exploration and worldwide weather fo-recasting .Mainframe computers (or mainframes )are large,powerful computers that many people can use at the same time .They are also expensive systems that are used for very large processing tasks and perform many important business and governmentapplicatoions .Minicomputers are smaller and more compact systems ,and fewer opra-tors can use them compared with a mainframe computer .They are usually found in medium-size businesses or in divisions within a large organization ,for example in gov-vernment department. Personal computers-also called microcomputers-are small,self-contained computers that fit on a desktop and usually only used by one person.they are the least exepensive type,and are widely used in business for a business for a variety of tasks,such as word processing ,small database management ,and spreadsheets.They are also used as home computers,for family budgeting and similar jobs,as well as for games. Protable compuers Another important development in personal computer technology is that the portable computers have been widely used .A small , portable personal computer is light and small enough to hold on your lap. The computer is smaller than a luggage but larger than a notebook,and is also called a laptop or notebook computer .A portable computer usually weighs between three to eight pounds,and when folded shut is about the size of a small briefcase .So it offers the user considerable freedom. The user can work his computer on train ,or on an airplane ,or on safari in Africa. Portable computers can be plugged in or run on batteries,although the batteries must be recharged very few hours .Battery power is a critical bottleneck,computers use a thin,mance and blocking further product miniaturization.Portable computer use a thin,lightweight display screen called a flat-panel display or a LCD monitor,rather than thecathode ray tube technology of large personal computers. Portable computer displays vary widely in quality. Typically, their display screens show fewer lines than displays on larger personal computers and can be difficult to read in bright light. Portable computers are self-contained units, having their own CPUs, memory, and many have modems and CD-ROM drives as well. While more expensive than a desktop computer with equivalent computing power, a portable computer van be ideal for the go-user who needs a second personal computer when he is out of desktop computers, since they can not be expanded or modified easily should your computing needs change. Also, the display is inferior to standard video graphics array (VGA) displays, although active matrix displays almost compete well except for size. The first portable computers, such as the Osborne and Compaq , are best described as “luggeables ”. These computers weighed in at more than 25 pounds and could not carried comfortably for more than a short distance. Todays portable computers, the laptop and notebook computers are much smaller and lighter.Systems Using MiscroprocessorsElectronic systems are used for handling information in the most general sense; this information may be telephone conversation, instrument reading or a companys accounts, but in each case the same main types of operation are involved; the processing, storage and transmission of information. In conventional electronic design these operations are combined at the function level; for example a counter, whether electronic or mechanical, stores the current count and increments it by one as required. A system such as an electronic clock which employs counters has its storage and processing capabilities spread throughout the system because each counter is able to store and process numbers.Present day microprocessor based systems depart from this conventional approach by separating the three functions of processing, storage, and transmission into different sections of the system. This partitioning into three main functions was devised by Von Neumann during the 1940s,and was not conceived especially for microcomputers. Almost every computer ever made has been designed with this structure, and despite the enormous range in their physical forms , they have all been of essentially the same basic design. In a microprocessor based system the processing will be performed in the microprocessor itself . The storage will be by means of memory circuits and the communication of information into and out of the system will be by means of special input/output(I/O) circuits. It would be impossible to identify a particular piece of hardware which performed the counting in a microprocessor based clock because the time would be stored in the memory and incremented at regular intervals by the microprocessor. However, the software which defined the systems behavior would contain sections that performed as counters. The apparently rather abstract approach to the architecture of the microprocessor and its associated circuits allows it to be very flexible in use, since the system is defined almost entirely in software. The design process is largely one of software engineering, and the similar problems of construction and maintenance which occur in conventional engineering are encountered when producing software .Figure 15.1 illustrates how these three sections within a microcomputer are connected in terms of the communication of information within the transfer of information between itself and the memory and input /ouput sections.The external connections relate to the rest(that is the non-computer part ) of the engineering system.Although only one storage section has been shown in the diagram , in practice two distinct types of memory RAM and ROM are used. In each case, the word” memory”is rather inappropriate since a computer memory is more like a filing cabinet in concept; information is stored in a set of numbered “boxes” and it is referenced by the serial number of the “box”in question.Microcomputers use RAM(Random Access Memory)into which data can be written and from which data can be read again when needed. This date can be read back from the memory in any sequence desired, and not necessarily the same order in which it was written, hence the waprwssion “random”access memory. Another type of ROM (Read Only Memory) is used to hold fixed patterns of information which cannot be affected by the microprocessor; these patterns are not lost when power is removed and are normally used to hold the program which defines the behavior of a microprocessor based system. ROMs can be read like RAMs , but unlike RAMs they cannot be used to store variable information . Some ROMs have their data patterns put in during manufacture, while others are programmable by the user by means of special equipment and are called programmable ROMs. The widely used programmable ROMs are erasable by means of special ultravioletlamps and are referred to as EPROMs, short for Erasable Programmable Read Only Memories .Other new types of device can be erased electrically without the need for ultravioletlight , which are called Electrically Erasable Programmable Read Only Memories, EEPROMs. The microprocessor processes data under the control of the porogram, controlling the flow of information to and from memory and input/output devices .Some input/output devices are general-purpose types while others are designed for controlling special hardware such as disc drives or controlling information transmission to other computers. Most types of I/O devices are programmable to some extent, allowing different modes of operation, while some actually contain special-purpose microprocessors to permit quite complex operations to be carried out without directly involving the main microprocessor.The microprocessor, memory and input/output circuit may all be contained on the same integrated circuit provided that the application does not require too much program or data storage. This is usually the case in low-cost application such as the controllers used inmicrowave ovens and automatic washing machines. The use of single package allows considerable cost savings to be made when articles are manufactured in large quantities. As technology develops , more and more powerful processors and larger and larger amounts of memory are being incorporated into single chip microcomputers with resulting saving in assembly costs in the final products . For the foreseeable future, however, ti will continue to be necessary to interconnect a number of integrated circuits to make a microcomputer whenever larger amounts of storage or input/output are required. Another major engineering application of microcomputers is in process control. Here the presence of the microcomputer is usually more apparent to the user because provision is normally made for programming the microcomputer for the particular application. In process control the benefits of fitting the entire system on to a single chip are usually outweighed by the high design cost involved, because this sort of equipment is produced in smaller quantities. Moreover, process controllers are usually more complicated so that it is more difficult to make them as single integrated circuits. In the former case the system would be programmed in conventional programming language such as the ones to be introduced later , while in the other case a special-purpose language might be used ,for example one which allowed the function of the controller to be described in terms of relay interconnections. In either case programs can be stored in RAM , which allows to be altered to suit changes in application , but this makes the overall system vulnerable to loss of power unless batteries are used to ensure continuity of supply. Alternatively programs can be stored in ROM ,in which case they virtually become part of the electronic “hardware” and are often referred to as firmware. More sophisticated process controllers require minicomputers for their implementation , although the use of large scale integrated circuits “blurs”the distinction between mini and microcomputers .products and process controllers of various kinds represent the majority of present-day microcomputer applications, the exact figures depending on ones interpretation of the word product.virtually all engineering and scientific uses of microcomputers can be assigned to one or these categories. 个人计算机什么是个人计算机按照容量大小，有许多类型的的计算机，例如巨型计算机，大型计算机，小型计算机和个人计算机。巨型计算机是一种特殊的、高容量的计算机，它主要被相当大的机构用以进行研究工作，在这些工作中，有石油勘探和全球气象预报。大型计算机（或主计算机结构）是一种大型的，可被许多人同时使用的强大计算机。它们也是昂贵的计算机系统，用于非常大的处理任务，并且完成许多重要的商务和政府应用任务，小型计算机是较小的、更紧凑系统，同大型计算机相比，只有少数操作员可以使用它们。它们常常会用在中型企业的内部的部门，例如政府部门中。个人计算机也称微型计算机是一种小型的适合于安放在桌面上的自足型计算机，并通常只由单人使用。这类计算机最为便宜，并广泛应用于商业中，来完成各种任务：比如文字处理小型数据库管理和数据表格制作。它们也用做家庭计算机，进行家庭财务预算和类似的工作，以及玩游戏。便携计算机（便携机）计算机技术的另一重要发展是便携机以被大量使用。小型的便携机轻巧的足以放在膝盖上操作。这种计算机比皮包要小，但比笔记本要大，还被称为膝上型或笔记本型计算机。便携机通常重在38磅之间，折起来后大约与小手提箱尺寸相当。所以他给了用户相当大的方便。用户可在火车上，飞机上，甚至在非洲旅行中使用计算。便携机可插上电源使用，也可用电池运行，尽管每隔几个小时电池必须充电。电池能量是一个亟待解决的瓶颈问题，限制了其运行性能，阻碍了产品进一步小型化。便携机使用又薄又轻的显示屏，称为平板显示器或LCD监视器。而不是使用较大的个人计算机中阴极线管技术。便携机显示器质量变化很大。一般来说其显示屏上的行数要比较大的个人计算机显示器的行数要少，并且在强光下较难读出。便携机是字自足型机器，有自己的CPU、存储器和磁盘驱动器，而且许多便携机带有调制解调器和CD-ROM. 便携机虽然比具有同等计算能力的台式计算机要贵些，但对走出办公室或旅行中需要第二台计算机的移动用户是理想的。 便携机并非总是台式机的替代品，因为当你的计算能力要求发生变化时，它们并不能方便地更改。而且显示器还比不上标准视频图形阵列显示器，尽管它的有源矩阵显示器除尺寸之外几乎能与之相媲美。第一批便携机，如 Osborne和 Compap，可形象地描述为“笨家伙”。这些计算机重量超过 25磅，并且不能方便地带到稍远的距离。今天的便携机、膝上型和笔记本型计算机就小得多、轻得多了。 微处理器化系统广义的说，电子系统是用于处理信息的，这种信息可以是电话会谈、仪器读数或企业帐户，但是各种情况下都涉及相同的主要操作：信息处理、存储和传送。在常规的电子设计中，这些操作都是一功能平台方式组合起来的，例如计数器，无论是电子还是机械的，都要存储当前值，并按要求将该值增1。诸如采用计数器的电子钟之类的任一系统要使存储和处理能力遍布整个系统，因为每个计数器都能存储和处理一些数字。当前微处理器系统与上述常规方法不同，它将处理、存储和传输三个功能分离形成不同的系统单元。这种形成三个主要单元的分离方法是冯。诺依曼在20世纪40年代所设想处来得，并且是针对微计算机的设想。从此几乎所有制成的计算机都是用这种结构设计的，尽管包含宽广的物理形式，从根本上来说它们均是具有相同的基本设计。在微处理器化系统中，处理是由微处理器本生完成的。存储是利用存储器电路，而进入和出自系统的信息传输则是利用特定的输入/输出（I/O）电路。要在一个微处理器化时钟中记数功能的一个特殊硬件是不可能的，因为时间存储在存储器中，而在固定的时间间隔下由微处理器控制增值。但是，规定系统运转过程的软件包含实现记数功能的单元。由于系统几乎完全由软件所定义，所以对微处理器结构和其辅助电路这种看起来非常抽象的处理方法使其在应用中非常灵活。这种设计过程主要是软件工程，而且在生产软件时，就会遇到产生于常规工程中相似的构造和维护问题。位型计算机中这三个单元是如何按照机器中的信息通信方式而连接起来的。该系统由微处理器控制，它管理自己与存储器和输入/输出单元的信息传输。外部的连接与工程系统的其余部分（即非计算机部分）有关。尽管图中显示的只有一个存储单元，实际中有RAM和ROM两种不同的存储器被使用。由于概念上的计算机