计算机的组成

Organizations of Computers   

　　Despite large variation in cost, size and capabilities，modern computers are remarkably similar in a number ways．Basically, a computer consists of four components as shown in Figure 1-1 (The lines connecting the various units represent possible paths of information flow. The arrows show the direction of information flows)．

　　All information that is to be processed by the computer must first be entered into the computer memory via an input device. The central processor manipulates the information in memory and the result of this manipulation is also stored in the memory the computer. Information in memory can be display through the use of appropriate output devices. These components and their interaction are described in more detail in the following sections.

1.Memory
　　The memory of a computer may be pictured as an ordered sequence of storage locations called memory cells Each cell is associated with a distinct ad-dress, which indicates its relative position in the se-quince. Figure 1-2 depicts a computer memory consisting of 1000 cells numbered consecutively from 0　to 999.Some large-scale computers have memories consisting of millions of cells．
    The memory cells of a computer are used to rep-resent information. All types of information—umbers, names, lists, and even pictures-may be represented in the memory of a computer. The information that is stored in memory cells is called the contents of memory cell．Every memory cell contains more than one data item. Whenever a data item is placed into a memory cell, any information already there is destroyed and cannot be retrieved. In Figure1-2, the contents of memory cell 3 is the number：26and the contents of memory cell 4 are the number: 2.5.
 
　　It is important to realize that the actual -instructions for manipulating data is also stored in the memory of the computer. These instructions are examined and carried out by the central processor unit. Described next.

2. The Central Processor Unit
　　The information representation capability of the computer would be of little use to us by itself. Indeed, it is the manipulative capability of the computer that enables us to study problems that would otherwise be impossible because of their computational requirements．
　　The heart of the manipulation capability of the computer is the Central Processor Unit (CPU). The CPU can retrieve information from the memory unit this information may be either data or instructions for manipulating data. The CPU can also store the result of manipulations back into the memory unit for later reference.
　　The CPU coordinates all activities of the various components of the computer. It determines which operations should be carried out and in what order. The transmission of coordinating control signals and commands is the function of the control unit within the central processor
　　Also found within the central processor in the arithmetic logic unit. The arithmetic portion consists of electronic circuitry that performs a variety of arithmetic operations, including addition, subtraction, multiplication and division. The time in which it can per-form these operations is on the order of a millionth of second. The logical unit consists of electronic circuitry to compare information and to make decisions based upon the results of the comparison. It is this feature, together with its powerful storage facility (the memory)，that distinguishes the computer from the simple hand-held calculators that many of us use. Most of these calculators can be used only to perform arithmetic operations on numbers；They cannot compare these numbers, make decisions，or store large quantities of numbers．

3.Input and Output Devices
　　The manipulative skills of the computer would be of little use to us if we were unable to communicate with the computer. Specifically, we must be able to enter information into the computer memory, and display information (usually the result of a manipulation) stored in the computer memory. The input de-vices are used to enter data into the computer memory; the output devices are used to display results in a readable form．
　　Most personal computers use a keyboard for input and a television-like monitor for output as shown in Figure 1-3.In addition, printing paper is to provide a permanent record of the computational results
　　In personal computer systems, a disk may be used to, provide additional capability for information storage and retrieval．A much larger quantity of in-formation may be stored on a disk platter (or diskette) than can fit in memory at one time. During a computer session, information saved previously is retrieved from a disk as needed and entered into the main memory where it is manipulated. Also, new information can be saved for future retrieval and use.

翻译：

计算机的组成

　　虽然计算机有着不同的大小以及各种各样的用途，现在的计算机（的组成）都基本相似。一台计算机由如图1-1所示的四个最基本的部分组成（图中不同组成部分之间的线条表示信息的通路，箭头表示信息传递的方向）。
　　在计算机中将要处理的信息都要通过输入设备送入内存；计算机，运算的结果也要存储在内存中。内存中的信息可以通过输出设备显示出来。上述几个基本部分和它们之间的联系将在以下的叙述中详述。

1.  存储器
    计算机中的存储器可以认为是一个连续的存储区域，它是由存储单元构成的，每一个存储甲一元都被赋予一个明确的地址用于表明它在存储队列中的相对位置。图1-2描述一个由一千个单元组成的存储区域，它们的编号是0-999.一些大型的计算机有上百万个的存储信息。
　　计算机的存储单元用于存储信息，所有类型的信息一一数字，名字，报表甚至图形都可以存储在计算机存储器中。存储单元中存放的信息叫做存储单元的内容，每个存储单元只能存放一个数据项，在任何时候，当一个数据被存放入一个存储单元时，原来存放的信息都将被破坏，而且不能恢复。在图1-2中0003存储单元是数字26, 0004存储
单元的是数字2.5。
　　操作指令和处理的数据都提存储在存储器中，认识到这一点非常重要。这些指令由中央处理器分析并且执行，下文将详述。

2.中央处理机
　　计算机光有存储数据的能力提不够的。事实上，计算机对数据配加工，处理能力更为重要，它使能够利用计算机来研究某些由于计算需求（过于庞大）而无法用其它计算工具解决的问题。
　　而对数据进行加工处理的核心部件就是中央处理器(CPU)。CPU能从存储器中获得信息，这些信息、可以是数据或对数据进行加工的指令．CPU还能将数据处理的结果返回到内存供以后引用。
　　CPU协调计算机中各部件的动作，它决定哪些操作将被执行以及执行的顺序。传递用于协调的控制和命令是（CPU中）控制单元的功能。
　　让我们来看一下CPU中的另一部件一一算术逻辑部件。其中的算术运算电路能进行加减乘除运算，运算速度可达每秒一百万次。逻辑运算电路具有比较（输入的）信息和依据（比较的）结果进行判断的能力。从特征上讲，正是由于有了逻辑运算部件和存储设备，才能将计算机与简易折（袖珍）计算器区别开来。大多数的计算器不能对数据进行比较、判断，也不能存放大量的数据。

3.输入输出设备
　　如果我们无法与计算机进行沟通（信息交换），计算机的加工处理能力将变得几乎没有用处。具体而言，我们必须能够将信息输入计算机的内存中去，能够将内存中的信息（通常是加工处理的结果）显示出来。输入设备通常用于向计算机中输入数据；输出设备则将结果以可阅读的形式显示出来。
　　大多数的个人计算机都采用键盘作为键入设备，而且一个与电视机屏幕类似的显示器作为输出设备（见图1-3），此外，还可用打印机将处理的结果永久地保存下来。在个人计算机系统中，磁盘用于提供额外的信息存储与恢复（到内存）的功能。磁盘可以存储大量的信息，其存储容量（甚至）超过了内存总容量。
　　在计算机工作时，一旦需要，就可将磁盘中的信息恢复到内存中去，进行处理，而一些（在处理过程中）新产生的信息也可以存储到磁盘中去供以后检索和使用。

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