計算機的組成

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.

翻譯：

計算機的組成

　　雖然計算機有著不同的大小以及各種各樣的用途，現在的計算機（的組成）都基本相似。一臺計算機由如圖1-1所示的四個最基本的部分組成（圖中不同組成部分之間的線條表示信息的通路，箭頭表示信息傳遞的方向）。
　　在計算機中將要處理的信息都要通過輸入設備送入內存；計算機，運算的結果也要存儲在內存中。內存中的信息可以通過輸出設備顯示出來。上述幾個基本部分和它們之間的聯系將在以下的敘述中詳述。

1.  存儲器
    計算機中的存儲器可以認為是一個連續的存儲區域，它是由存儲單元構成的，每一個存儲甲一元都被賦予一個明確的地址用于表明它在存儲隊列中的相對位置。圖1-2描述一個由一千個單元組成的存儲區域，它們的編號是0-999.一些大型的計算機有上百萬個的存儲信息。
　　計算機的存儲單元用于存儲信息，所有類型的信息一一數字，名字，報表甚至圖形都可以存儲在計算機存儲器中。存儲單元中存放的信息叫做存儲單元的內容，每個存儲單元只能存放一個數據項，在任何時候，當一個數據被存放入一個存儲單元時，原來存放的信息都將被破壞，而且不能恢復。在圖1-2中0003存儲單元是數字26, 0004存儲
單元的是數字2.5。
　　操作指令和處理的數據都提存儲在存儲器中，認識到這一點非常重要。這些指令由中央處理器分析并且執行，下文將詳述。

2.中央處理機
　　計算機光有存儲數據的能力提不夠的。事實上，計算機對數據配加工，處理能力更為重要，它使能夠利用計算機來研究某些由于計算需求（過于龐大）而無法用其它計算工具解決的問題。
　　而對數據進行加工處理的核心部件就是中央處理器(CPU)。CPU能從存儲器中獲得信息，這些信息、可以是數據或對數據進行加工的指令．CPU還能將數據處理的結果返回到內存供以后引用。
　　CPU協調計算機中各部件的動作，它決定哪些操作將被執行以及執行的順序。傳遞用于協調的控制和命令是（CPU中）控制單元的功能。
　　讓我們來看一下CPU中的另一部件一一算術邏輯部件。其中的算術運算電路能進行加減乘除運算，運算速度可達每秒一百萬次。邏輯運算電路具有比較（輸入的）信息和依據（比較的）結果進行判斷的能力。從特征上講，正是由于有了邏輯運算部件和存儲設備，才能將計算機與簡易折（袖珍）計算器區別開來。大多數的計算器不能對數據進行比較、判斷，也不能存放大量的數據。

3.輸入輸出設備
　　如果我們無法與計算機進行溝通（信息交換），計算機的加工處理能力將變得幾乎沒有用處。具體而言，我們必須能夠將信息輸入計算機的內存中去，能夠將內存中的信息（通常是加工處理的結果）顯示出來。輸入設備通常用于向計算機中輸入數據；輸出設備則將結果以可閱讀的形式顯示出來。
　　大多數的個人計算機都采用鍵盤作為鍵入設備，而且一個與電視機屏幕類似的顯示器作為輸出設備（見圖1-3），此外，還可用打印機將處理的結果永久地保存下來。在個人計算機系統中，磁盤用于提供額外的信息存儲與恢復（到內存）的功能。磁盤可以存儲大量的信息，其存儲容量（甚至）超過了內存總容量。
　　在計算機工作時，一旦需要，就可將磁盤中的信息恢復到內存中去，進行處理，而一些（在處理過程中）新產生的信息也可以存儲到磁盤中去供以后檢索和使用。

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