Unit 1 Computer Technologies

which the user desires the system to accomplish to the computer. The usefulness of the computer lies in its ability to execute the instructions quickly and accurately. 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. Regardless of the application, the computer executes the program through its ability to manipulate data and numbers in their most elementary form. The data
accordance with a predetermined program of instructions. The computer itself is referred to as hardware, whereas the various programs are referred to as software. 多种用途的 There are three basic hardware components of a general-purpose digital computer: ￭ Central processing unit （CPU） ￭ Memory 内存 输入/输出接口 中央处理器
ห้องสมุดไป่ตู้
and numbers are represented in the computer by electrical signals which can take 二进制的 on of two alternative states. This form of representation is called the binary 十进制的 system. The more familiar decimal number system and a whole host of software languages can utilize the binary system to permit communication between
hold, and transfer data. Each register consists of binary cells to hold bits of data. 确定 The number of bits in the register establishes the word length with which the
computer is capable of handling. The number of bits per word can be as few as 4 （early microcomputers） or as many as 64 （large scientific computers）.
Unit 1 Computer Technologies
Computer Aided Design Computer Aided Manufacturing 数字的、计数的 组成部分 The central and essential ingredient of CAD/CAM is the digital computer. Its 天生的、固有的 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
￭ Input/output （I/O）section
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 算术逻辑运算器 and an arithmetic-logic unit（ALU）. The control unit coordinates the operations of all the other components. It controls the input and output of
provided by a set of instructions called an executive program which is stored in
memory.
The arithmetic-logic unit performs operations such as addition, subtractions, and comparisons. These operations are carried out on data in binary form. The 顺序、次序、序列 logic section can also be used to alter the sequence in which instructions are executed when certain conditions are indicated and to perform other functions, 屏蔽 such as editing and masking data for arithmetic operations. Both the control unit and the arithmetic-logic unit perform their functions by 寄存器 utilizing registers. Computer registers are small memory devices that can receive,
information between the computer and the outside world through the I/O section, 使同步发生 synchronizes the transference of signals between the various sections of the computer, and commands the other sections in the performance of their functions. The arithmetic-logic unit carries out the arithmetic and logic manipulations of data. It adds, subtracts, multiplies, divides, and compares numbers according to programmed instructions. The memory of the computer is the storage unit. The data stored in this section are arranged in the form of words which can be conveniently transferred to the ALU or I/O section for processing. Finally, the input/output provides the means for the computer to communicate with the 外围的 external world. This communication is accomplished through peripheral equipment such as readers, printers, and process interface devices. The computer may also be connected to external storage units （e.g., tapes, disks, etc.） through the I/O section of the computer.
Introduction
manually. To understand CAD/CAM, it is important to be familiar with the
concepts and technology of the digital computer. The modern digital computer is an electronic machine that can perform 逻辑的 mathematical and logical calculations and data processing functions in
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
computers and human beings.