Unit 1 Computer Technologies IntroductionAs we know,the central and essential ingredient[组成部分]of CAD/CAM is the digital computer.[1]Therefore,to understand CAD/CAM,it is important to be familiar with the concepts and technology of the digital computer.There are three basic hardware components of a general-purpose digital computer:1.Central processing unit (CPU)2.Memory3.Input/output(I/O)sectionFig.1.1 Basic hardware strucure of a digital computerControl UnitCPUArithmetic-logic [算术逻辑]UnitComputer Programming Languages1.Machine language2.Assembly language[汇编语言]3.Procedure-oriented(high-level) languages[程序导向(高级)语言]Computer Process InterfacingSome of the important components of a computer process control system.(1)Manufacturing process data.These data can be classified into three categories:1) Continuous analog signals [连续模拟信号]2) Discrete binary data [离散二进制数据]3) Pulse [脉冲] data(2)System interpretation of process data.There are six categories of computer-process interface representing the inputs and outputs for the three types of process data.They are:6) Pulse generators1)Analog to digital2)Contact input3) Pulse counters4) Digital to analog5)Contact outputCategoriesComputer Network StructuresThe various network arrangements divide themselves into several basic categories,and we mainly introduce five of the most common used categories.Network Protocols and OSI System Structure(1) Physical layer(2) Data link layer(3) Network layerSeven Layers(4) Transport layer(5) Session layer [会话层](6) Presentation layer(7) Application layer [应用层]Fig.1.3 Structure of ISO/OSI System ModelInternet Application and DevelopmentNowadays,more and more computers and devices are connected with internet system,more and more service and information can be offered by the utilization of internet.It is developing by an incredibly speed and it has become an indispendable component of human's civilization.Control UnitThe control unit coordinates the operations of all the other components.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 functionsArithmetic-logic UnitThe arithmetic-logic unit carries out the arithmetic and logic manipulations[操作]of data. It adds,subtracts,multiplies,divides,and compares numbers according to programmed instructions.Machine LanguageThe language used by the computer is called machine language.It is written in binary,with each instruction containing an operation code and an operand.On the whole,programming in machine language is tedious,complicated,and time-consuming.Assembly LanguageA language consisting of mnemonic instructions is called an assembly language.It is considered to be one kind of low-level language.Assembly language programs must be converted into machine language before the computer can execute them.High-level LanguagesHigh-level languages are procedure oriented.The program written on one computer can be run on a different computer without any significant modifications to the program.It is not necessary for the programmer to be familiar with the machine language through using the high-level languages.Fig.1.2Types of computer network structuresa)Point-to-point.b)Multidrop.c)Star.d)Loop.e)TreeNotes1. The central and essential ingredient of CAD/CAM is the digitalcomputer.分析：CAD/CAM——计算机辅助设计与计算机辅助制造集成系统。
句意：CAD/CAM的核心部分是计算机。
2．Signal conditioners, which filter random electrical noise and smooth the analog signal emanating from transducing device.句意：信号调整器，它可滤掉杂乱的电噪声，并可修整由传感装置送出的模拟信号。
3．A pulse counter is used to convert the pulse trains into a digital representation, which is then applied to the computer’s input channel.分析：be applied to ——适用于。
句意：脉冲记数器可将脉冲串转换为一种数字代码，以适合于计算机输入通道。
4．This results from the shared nature of the communication lines.分析：the shared nature of the communication lines——通信线的共享特性。
句意：这来自通信线的共享特性。
5．Messages to a specific computer are usually transmitted to all computers in the network, with the addressee decoding itsaddress and accepting the information.分析：With——同时。
句意：送往某特定计算机的信息，一般都传送到网络中的所有计算机，同时由信息接收计算机译出地址码并接收信息。
6．In a network, all computers are connected and communicated with each other according to some kinds of enacted regulations or agreement, which is called “network protocols”分析：Network Protocols—网络协议句意：在网络中，所有的计算机都根据一些规则和协议进行连接和通信，规则和协议称为网络协议。