Kategorie: Informatika (celkem: 338 referátů a seminárek)

Informace o referátu:

  • Přidal/a: anonymous
  • Datum přidání: 06. února 2007
  • Zobrazeno: 2008×

Příbuzná témata



Computer, electronic device that can receive a set of instructions, or program, and then carry out this program by performing calculations on numerical data or by manipulating other forms of information.

The modern world of high technology could not have come about except for the development of the computer. Different types and sizes of computers find uses throughout society in the storage and handling of data, from secret governmental files to banking transactions to private household accounts. Computers have opened up a new era in manufacturing through the techniques of automation, and they have enhanced modern communication systems. They are essential tools in almost every field of research and applied technology, from constructing models of the universe to producing tomorrow's weather reports, and their use has in itself opened up new areas of conjecture. Database services and computer networks make available a great variety of information sources. The same advanced techniques also make possible invasions of personal and business privacy. Computer crime has become one of the many risks that are part of the price of modern technology.

Types of Computers

Two main types of computers are in use today, analogue and digital. Analogue 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 calculations and by dealing with each number digit by digit.

Installations that contain elements of both digital and analogue 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 analogue form can also be fed into a digital computer by means of an analogue-to-digital converter, and the same is true of the reverse situation (see Digital-to-Analogue Converter).

Analogue Computers

The simplest analogue calculating device is the slide rule, which employs specially calibrated scales to facilitate multiplication, division, and other functions. The analogue computer is a more sophisticated electronic or hydraulic device that is designed to handle input in terms of, for example, voltage levels or hydraulic pressures, rather than numerical data.

In a typical electronic analogue 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 whether 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 100 MHz-a fairly representative speed for a microcomputer-is capable of executing 100 million discrete operations each second. Supercomputers used in research and defence 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 (0-3) 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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