types of digital computer

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1. amomipais82
   

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                     Types of Computers
                     Two main types of computers are in use today, analog and digital, although the term computer is often used to mean only the digital type. Analog computers exploit the mathematical similarity between physical interrelationships in certain problems, and employ electronic or hydraulic circuits (see Fluidics) to simulate the physical problem. Digital computers solve problems by performing sums and by dealing with each number digit by digit.
                     Installations that contain elements of both digital and analog computers are called hybrid computers. They are usually used for problems in which large numbers of complex equations, known as time integrals, are to be computed. Data in analog form can also be fed into a digital computer by means of an analog- to-digital converter, and the same is true of the reverse situation.
   
                     Analog Computers
                     The analog computer is an electronic or hydraulic device that is designed to handle input in terms of, for example, voltage levels or hydraulic pressures, rather than numerical data. The simplest analog calculating device is the slide rule, which employs lengths of specially calibrated scales to facilitate multiplication, division, and other functions. In a typical electronic analog computer, the inputs are converted into voltages that may be added or multiplied using specially designed circuit elements. The answers are continuously generated for display or for conversion to another desired form.
   
                     Digital Computers
                     Everything that a digital computer does is based on one operation: the ability to determine if a switch, or "gate," is open or closed. That is, the computer can recognize only two states in any of its microscopic circuits: on or off, high voltage or low voltage, or-in the case of numbers-0 or 1. The speed at which the computer performs this simple act, however, is what makes it a marvel of modern technology. Computer speeds are measured in megaHertz, or millions of cycles per second. A computer with a "clock speed" of 33 mHz is capable of executing 33 million discrete operations each second. Business microcomputers can perform 60 to 100 million operations per second, and supercomputers used in research and defense applications attain speeds of billions of cycles per second.
                     Digital computer speed and calculating power are further enhanced by the amount of data handled during each cycle. If a computer checks only one switch at a time, that switch can represent only two commands or numbers; thus ON would symbolize one operation or number, and OFF would symbolize another. By checking groups of switches linked as a unit, however, the computer increases the number of operations it can recognize at each cycle. For example, a computer that checks two switches at one time can represent four numbers (0 to 3) or can execute one of four instructions at each cycle, one for each of the following switch patterns: OFF-OFF (0); OFF-ON (1); ON-OFF (2); or ON-ON (3).
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