計算機的分類

Classification of Computers

1 ．Digital, Analog, and Hybrid Computers
　　A digital computer is a counting device that operates on discrete data. It operates by directly counting numbers (or digits) that represent numbers, letters，or other special symbols．Just as digital watches directly count off the seconds and minutes in an hour, digital processors also count discrete values to achieve the desired out put results．
　　In contrast to digital processors, however, there are also analog computers that do not compute directly with numbers．Rather, they deal with variables that are measured along a continuous scale and are recorded to some predetermined degree of aclearcase/" target="_blank" >ccuracy Temperature, for example, may be measured to the nearest tenth of a degree on the Celsius scale, voltage may be measured to the nearest hundredth of a volt, and pressure may be measured to the nearest "pound per square inch” value. Analog computing systems are frequently used to control processes such as those found in an oil refinery where flow temperature measurements are important．
　　Desirable features of analog and digital machines are sometimes combined to create a hybrid computing system. In a hospital intensive-care unit, for example, analog devices may measure a patient's heart function, temperature, and other vital signs．These measurements may then be converted into numbers and supplied to a digital component in the system. This component is used to monitor the patient's vital signs and to send an immediate signal to the nurse's station if any abnormal readings are detected ．
　　Analog and hybrid processors obviously perform important specialized tasks．But the overwhelming majority of all computers used for business and scientific applications are digital devices．

2. General-Purpose and Special-Purpose Digital Computers
　　Digital computers are made for both special and general uses．As the name suggests，a special-purpose computer is one that's designed to perform only one specific task．The program of instructions is wired into or permanently stored in such a machine. Al-though it lacks versatility it does its single task quickly and efficiently.
　　Special purpose processors designed just to solve complex navigational problems are installed aboard U. S. atomic submarines．Not too long ago, however, special-purpose computers were too expensive for most applications．Only a few might be needed by one organization, and the specialized model might not do anyone else any good. But today, customized microcomputers are produced in large quantities to perform tasks such as monitoring household appliance and controlling the fuel, ignition, and instrument systems in automobiles．Furthermore, rapid progress is now being made in developing the automated design tools that engineers can use to economically build small quantities of complex microcomputer chips for specialized purposes．
　　A general-purpose computer is one that can store different programs and can thus be used in countless applications．You have seen that by using different instructions such a machine can process a payroll one minute and a billing application the next. New pro-grams can be written, and old programs can be changed o dropped. The versatility of general-purpose stem is limited only by human imagination. And so, unless otherwise noted，all our future discussion of “computer” will be about general purpose digital systems

3 Micro, Mini，Mainframe and Super Computers
　　All computer system of interest to us is similar that they contain hardware components for input, central processing, and output. They all perform basic machine operations under the direction of stored programs, which can be quickly changed to permit the Processing of a stream of different applications. Of course, widely different sorts of applications require different system resources to process them. In other words, the personal computer used in the home to play Space Invaders would hardly be used in NASA missions control to monitor an actual space shuttle launch.
　　Modern computers vary in physical size from those that fill rooms to those with CPUs the size of amide. Generally, the larger the system, the greater is its processing speed, storage capacity, and cost. Also, the larger systems are better equipped to handle a greater number of more powerful input and output devices.
　　Systems on the low end of the size scale are called microcomputers or minicomputers. Microcomputers or personal computers are the smallest general-purpose systems．But they may perform the same operations and use the same program instructions as much larger computers. Minicomputers are also small general-purpose systems. The are topical more powerful and expensive than micros，although the performance of some newer micros may surpass the capabilities or some older minis. In physical size, minis can vary from a desktop model to a unit the size of a small file cab.net.
　　Continuing up the size scale, mainframe computers are system that may offer faster processing speeds and greater storage capacity than a typical mini．A whole series of mainframe models ranging in size from small to very large are generally lumped to-getter under family designation by mainframe manufacturers．There is quite a bit of overlap possible in the cost, speed, and storage capacity of larger minis and smaller mainframes．
　　Finally come the supercomputers, designed to process complex scientific applications．These systems are the largest, fastest.

翻譯：

計算機的分類

1．數字、模擬和混合計算機   
　　數字計算機是對離散數據進行操作的計算設備。它直接對表示數字、字母或其它專用符號的數進行計算。正如數字表以秒、分來計算小時那樣，數字處理器也對離散數值進行計算以獲得所需要的輸出結果。
　　還存在一種與數字計算機相反的模擬計算機，它不直接對數進行計算。模擬計算機處理在連續標度上測量的變量并按預先規定的精度進行記錄。例如：測量時，溫度可精確到1/10攝氏度，電壓可精確到1/100伏，壓力可精確到“磅／平方英寸”。模擬計算機系統常用于控制諸如煉油廠中的流量和溫度測量過程。
　　有時把模擬計算機和數字計算機的優點結合起來形成一個混合計算機系統。例如在醫院使用的監護器中，模擬部件可用于測量病號的心功能、溫度和其它生理癥狀。然后把這些測量信號轉換成數字并送給系統的數字部件，該部件用于監視病員的生理癥狀，當檢測到異常信號時，向護士值班室發出報警信號。
　　很明顯，模擬和混合處理器用于完成重要的特定任務。但絕大多數商業和科學的計算機是數字計算機。

2.通用和專用數字計算機
　　數字計算機可分為專用的和通用的。正如它們的名字所表示的，專用計算機是完成某一專門任務的計算機，其指令程序是固化或永久存儲在該機器上的，雖然它缺乏通用性，但它執行單一任務時很快，效率很高。
　　為了解決復雜的導航問題，美國將幾個專用處理器裝在了核潛艇上。但是，專用計算機對大多數用戶來講仍然很昂貴。一個部門對專用計算機需求很少，而專用方式不能很好完成其它任務?，F在，客戶定制的微型計算機己大量生產，它們用于完成諸如監視家庭設施、控制燃料、點火以及汽車中的儀表系統。目前自動設計工具得到了快速發展，工程師可用這些工具為個別用戶設計復雜的專用微型計算機芯片。
    通用計算機是一種可存儲不同程序的，應用無可估量的計算機。己看到了，一臺機器使用不同的命令，可在這一分種內計算機工資單，在下一分種開出賬單?？梢詫懗鲂鲁绦蚨幕蛉サ襞f程序。通用計算機的通用性只是受人們創造力的限制。因此，除非特別說明，以后所討論的計算抓都是指通用數字系統。

3.微型、小型、大型計算機和超級計算機
　　所有目前使用的計算機，它們的輸入設備、中央處理器和輸出設備的硬件都是相似的。所有這些機器都是在存儲程序的指導下完成基本的機器操作，而存儲可很性地改變以處理其它不同的任務當然，種類繁多的應用要求不同的系統資源去處理。換句話說，家中玩空中大戰的個人計算機決不可能用于宇航局監視航天飛機發射的飛行控制計算機。
　　現代的計算機，其規?？梢允菐组g屋子那么大，也可以是硬幣大小?？偟膩碇v，系統越龐大，其處理速度越高，存儲量越大，價格越高。同時，系統越龐大，越應配備更多的、功能更強的輸入和輸出設備。
　　規模最小的系統 叫做微型計算機或小型計算機。微型計算機或個人計算是最小的通用系統。但它們使用與大型計算機相同的程序指令來完成同一操作，小型計算機也是小見通用系統。盡管某些新的微型計算機的性能已超過某些舊的小型機，但一般來講小型機比微型計算機功能更強，更貴。小型機的規模小可為臺式，大可為一個小型文件柜。
　　隨著規模的增加，就形成了大型計算機，它比一般的小型機有更快的處理速度和更大的存儲容量。大型計算機廠家把它們的主機從規模小的小型機到非常大的大型機設計成系列產品。較大的小型機和較小的大型機之間在價格、速度和存儲器容量上全可能有重迭。
　　最后是超級計算機，它用于處理更復雜的科學問題，這種計算機規模最大、速度最快。

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