Unit 1 计算机技术Introduction前言The central and essential ingredient of GAD/CAMis the digital computer.1Its inherent speed and storage capacity have made it possible to achieve the advances in image processing, real-time process control, and a multitude of other important functions that are simply too complex and time-consuming to perform manually. To understand CAD/CAM it is important to be familiar with the concepts and technology of the digital computerCAD/CAM的重要组成部分是数字计算机，它固有的速度以及存储能力似的它能够在图像处理，实时过程控制以及很多因太复杂太费时而人工无法完成的其他重要功能方面获得进步，要想懂得CAD/CAM，熟悉数字电脑的概念和技术是很重要的.The modern digital computer is an electronic machine that can perform mathematical and logical calculations and data processing functions in accordance with a predetermined program of instructions. The computer itself is referred to as hardware, whereas the various programs are referred to as software.现在数字计算机是一部能够根据预定的程序来完成数字和逻辑运算以及数据处理功能的电子设备，计算机本身称为硬件，而各种各样的程序称为软件There are three basic hardware components of a general-purpose digital computer;一般用途的数字计算机由三种基本硬件组成 .Central processing unit (CPU) 微处理器 .Memory存储器 .Input/output ( I/0 )section输入/输出设备The relationship of these three components is illustrated in Fig. 1.1. The central processing unit is often considered to consist of two subsections; a control unit and an arithmetic-logic unit (ALU). 这三个组成部分的关系如图1.1所示，中央处理器通常被认为包含两部分:一个控制器和一个运算器.The control unit coordinates the operations of all the other components. 控制器控制所有其他组成部分的运输。It controls the input and output of information between the computer and the outside world through the I/O section, synchronizes the transference of signals between the various sections of the computer, and commands the other sections in the performance of their functions.它通过输入/输出端口控制电脑与外围设备之间信息的输入与输出、控制电脑各部分间信号的传输，同时也控制其他部分完成各自的功能。 The arithmetic-logic unit carries out the arithmetic and logic manipulations of data. 运算器完成数据的算术和逻辑运算。 It adds, subtracts, multiplies, divides, and compares numbers according to programmed instructions. The memory of the computer is the storage unit. 它根据编制的程序完成数的加、减、乘、除和比较。存储器完成电脑的记忆功能。The data stored in this section are arranged in the form of words which can be conveniently transferred to the ALU or I/0 section for processing.数据被转译成便于向运算器和输入/输出设备传输以进行处理的字节形式存储在该部分中Finally, the input/output provides the means for the computer to communicate with the external world. This communication is accomplished through peripheral equipment such as readers, printers, and process interface devices. 最后，输入/输出设备提供电脑和外部世界的交流手段，这种交流通过像阅读机、打印机和出口设备等外围设备完成。 The computer may also be connected to external storage units (e. g，tapes, disks, etc) through the UO section of the computer电脑也可以通过输入/输出设备与外围存储设备（比如磁带、磁盘）链接。. The software consists of the programs and instructions stored in memory and in external storage units. It is the software that assigns the various functions which the user desires the system to accomplish to the computer. 软件由程序和存储在内存与外存中的指令组成。软件将使用者所要求系统完成的各项功能分配给计算机。 The usefulness of the computer lies in its ability to execute the instructions quickly and accurately. 电脑的有用性在于它快速准确地执行程序的能力。 Because the contents of the computer s memory can be easily changed, and therefore different programs can be placed into memory, the digital computer can be used for a wide variety of applications.因为电脑存储的内容你能够很容易被改变，并且不同的程序都能够被存入，所以数字电脑能够用于多种应用。Regardless of the application, the computer executes the program through its ability to manipulate data and numbers in their most elementary form. 不考虑这些应用，电脑能自动执行程序并以最基本的形式完成数字和数据的运算。 The data and numbers are represented in the computer by electrical signals which can take one of two alternative states.数据和数字在电脑中以两种形式的电信号的一种表示。This form of representation is called the binary system. 这种表示形式叫做二进制计数法。The more familiar decimal number system and a whole host of soft-ware languages can utilize the binary system to permit communication between computers and human beings.更多与之类似的十进制计数法以及很多软件语言利用二进制计数法在电脑和人之间实现交流。Central Processing Unit (CPU) 中央处理器 The central processing unit (CPU) regulates the operation of all system components and performs the arithmetic and logical operations on the data. 中央处理器控制所有系统组成的操作并进行数据的算术和逻辑运算。To accomplish these functions, the CPU consists of two operating units:为了完成这些功能，中央处理器包含两个结构单元： .Control unit Arithmetic-logic unit (ALU) 控制器、运算器The control unit coordinates the various operations specified by the program instructions. 控制器控制由程序制定的各种操作。These operations include receiving data which enter the computer and deciding how and when the data should be processed. The control unit directs the operation of the arithmetic-logic unit.这些操作包括接收输入电脑的数据和决定数据的处理形式以及处理时间，控制器控制运算器的操作。 It sends data to the ALU and tells the ALU what functions to perform on the data and where to store the results. 它将数据发送给运算器并告知运算器数据所要求的处理操作和结果的存储位置。The capability of the control unit to accomplish these operations is provided by a set of instructions called an executive program which is stored in