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[ The PC Guide | Introduction to the PC | How the PC Works | How the Computer Computes ]

Digital and Analog Information

There are two ways to represent information. Information that is continuous, that is, any piece of information that can take on any of an infinite set of values, is said to be analog. For example, the time, the temperature, the speed of your car--all of these have a continuous range of values. While you say, for example, that it is 55 degrees outside, it could really be 55.12492 degrees, or any value between that and 55.

Digital information is restricted to a finite set of values. For example, a traffic light is (normally) red, yellow or green; not "yellow-green" or orange. Computers use a form of digital information called binary information. Here, the information is restricted to only two values: one or zero. Computers use binary information for several reasons:

  • Simplicity: It is the simplest, most compact and least ambiguous way to express information about something: for example, zero=off and one=on could be used to represent the status of a regular light bulb.
  • Expandability: It is easy to build on and expand: you can use two binary values together to represent the status of two light bulbs.
  • Clarity: Errors are reduced when a value can only be one or zero; the computer knows there are no values in between, which is useful when electrical signals become "dirty". If a 0.95 value shows up on your modem line, the computer knows it is probably really a 1, since 0.95 isn't a valid value. It will interpret the 0.95 as a 1, and no data will be lost as a result.
  • Speed: Computers make millions of decisions a second, and these decisions are easier to make when the number of values is small.

Digital information is often represented only in binary form, but does not have to be. A good example is compact disk audio, where sound information is stored as digital samples. The advantage of digital sampling is that the information is the same every time it is read, so there is no "loss" in quality over time as found in conventional magnetic analog storage media.

Next: The Mathematics of Computing

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