微型计算机的奇妙结构

　　In Chinese， a computer is popularly known as an " electrical brain"， for the working process of a computer is similar to a human brain very much.

　　In appearance， a microcomputer has three simple and apparent parts： the main frame， the keyboard and the monitor. In other words， if you own these parts， you would exactly have a computer. A computer system is composed of software and hardware in the light of its working mode. If we compare the hardware to a human body， then， the software would be soul.

　　Just as a driver can't drive a car without driving skills or the car itself， you can't control a computer without controlling techniques or the computer itself. The controlling techniques are called software， while computers themselves and related devices are called hardware.

　　The work of a computer is just making full use of various resources by software set in the computer， and directing the hardware to realize marvelous omnipotent functions.

　　Primary Components of a Microcomputer

　　There are many types of microcomputers. Here， we will use an IBM Personal Computer （PC） to illustrate the primary components of a microcomputer. Other brands and models of microcomputers exhibit difference in appearance and operations. An IBM PC is shown in the figure. Its primary hardware components are the main frame， the monitor， the keyboard， and many peripherals such as the disk drive， hard disk， printer， and mouse， all of which are hardwired to the main frame. The main frame is the heart of a microcomputer system. It contains the Central Processing Unit （CPU）， a chip that controls the major operations of the computer and the main memory.

　　Floppy and Hard Disks

　　The typical secondary storage medium of a microcomputer is the floppy and hard disks. A floppy disk， or diskette， is a thin circular piece of flexible polyester coated with a magnetic material. The data are recorded on a series of concentric circles called tracks. The access mechanism steps from track to track， reading or writing one track at a time. A track is subdivided into sectors. To distinguish the sectors， they are sequentially addressed by natural numbers 0，1，2and so on .A sector is a primitive access unit.

　　Most microcomputers use floppy diskettes of 5 1/4 inches and 3 1/2inches in diameter. The following figure shows a 3 1/2 inches floppy diskette.

　　Hard disks， or fixed disks， can be either fixed in the mainframe as a part of the internal hard disks reside permanently within the microcomputer and are removed only for servicing or replacement. External hard disks can be purchased alone and then attached to the microcomputer with cables； they are used for backing up large amounts of data or for additional storage capacity. Hard disks provide tremendous storage capacities ranging from hundreds of megabytes to several gigabytes.

　　Keyboard　and Mouse

　　A keyboard is a requisite hardware device of a computer. It is an input device most in use， and a dialogue tool between a man and a computer. We can input data needed to be processed or preserved by a computer via a keyboard.

　　A typical includes a group of standard keys set in the center of the keyboard， many function keys and several additional keys. Function and additional keys have different roles in different software.

　　Another popular input device is mouse. The mouse is a small， handheld object that is pushed around a desktop to move the cursor on the screen or to select choices from menus displayed on the screen. A mouse is essentially a pointing device that allows the user to do many operations more quickly than he could with the keyboard alone.

　　Monitor

　　The monitor is an essential output device of a microcomputer. Monitors， also known as video display terminals （VDTs）， resemble television screens， and may be either monochrome or color. A monochrome monitor displays only one color on the screen. It is possible white or more eyepleasing green. While color monitors usually offer a wide selection of display colors.

　　Printer

　　The printer is the most commonly used output device after the monitor. Printers can create a permanent paper copy of results generated by the program being run on the computer. These printouts are sometimes referred to as hard copy. Printers can also generate listings of programs and graphic images. Three types of printers are available： wire printers， ink jet printers and laser printers.

　　在中文里，计算机有一个人所共知的雅号："电脑".这是因为计算机的工作过程与人的大脑思维过程极为相似。

　　从外表上看，微型计算机有简单而鲜明的三部分：主机、键盘和监视器。换句话说，只要你拥有了这三部分，你就确实拥有一台微型计算机。从计算机的工作过程看，计算机系统是由软件和硬件组成的。如果你将硬件比作人的躯体，那么，软件就好比人的灵魂。

　　正像没有汽车或者没有汽车驾驶技术，司机就不能驾驶汽车一样，没有计算机或者没有控制计算机的技术，人就不能操纵计算机。这些控制计算机的技术被叫作软件，计算机及其各种设备本身被叫作硬件。

　　计算机的工作就是通过计算机的软件组，充分利用计算机的各种资源，并指挥硬件实现无所不能的奇妙用途。

　　微型计算机的主要组成部分

　　微型计算机种类繁多。在这里，我们用IBM 个人计算机（PC）来解释微型计算机的主要组成部分。其他品牌和型号的微机在外貌和操作上各有不同。一台IBM　PC计算机如图所示：它的主要硬件成分是主机、监视器、键盘以及许多与主机相连的外围设备，如磁盘驱动器、硬盘、打印机、鼠标。主机是微机系统的核心，它包括中央处理单元（CPU）和主存， CPU是一块控制计算机主要操作的芯片。

　　软盘和硬盘

　　微型计算机的典型的辅助存储介质是软盘和硬盘。软盘是一个表面附有磁性材料的柔性的聚酯材料做成的圆圆的薄片。数据被记录在一些被称为磁道的同心圆上，存取装置读写磁道的过程是从一个磁道到另一个磁道，一次只读写一个磁道。磁道又分为扇区，为了区分这些扇区，用0、1、2等给扇区按顺序编上地址号，一个扇区是一个基本的存取单位。

　　大多数的微机使用5　1/4和3　1/2英寸的软盘，下图示的是一张3　1/2英寸的软盘。

　　硬盘，又称固定盘，它既可以固定在主机箱内成为微机内部设计的一部分，也可以是独立的外部单元。内部硬盘永久性地安置在微机内，只有需维修或更换时才取出。外部硬盘可以独立购买，通过电缆线与微机相连；它的用处是备份大量的数据或增加存储容量。硬盘的存储容量从几百兆字节不等。

　　键盘和鼠标

　　键盘是计算机的一具必要的硬件设备，也是最常用的一种输入设备，是人与计算机的对话工具。我们可以通过键盘把数据、资料等需要计算机处理或保存的信息送入计算机。

　　一个典型的键盘包括一组位于键盘中间的标准键、许多功能键和一些附加键。功能键和附加键在不同的软件中有不同的软件中有不同的作用。

　　另一种常用的输入设备是鼠标。鼠标是一个可以用手在桌面上推动的小东西，通过它可以在屏幕上移动光标或者选中菜单上的某项功能。鼠标是一个必要的外部设备，它可以使用户以比仅使用键盘快得多的速度完成许多操作。

　　显示器

　　显示器是微机必需的输出设备。显示器类似于电视屏幕，也被称为视频显示终端（VDTs），有单色显示器和彩色显示器。单色显示器屏幕上仅显示一种颜色，这可能是白色或是一种更悦目的绿色。彩色显示器通常提供许多种可供选择的单色。

　　打印机

　　打印机是除显示器外最常用的输出设备。打印机可以将程序运行的结果打印出来，从而成为永久的纸拷贝。这种打印输出有时也被称为硬拷贝。打印机也可以打印程序列表和图形图片。有三种类型的打印机：外打式打印机、喷墨打印机和激光打印机。