How a PC represents information

One of the most amazing things about a PC is its apparent ability to understand information that is fed into it via a keyboard or mouse. The fact is computers can understand very little. All they can do is recognise two distinct physical states produced by electricity, magnetic polarity or reflective light. Essentially, they can only understand whether a switch is on or off.

To a computer everything is a number. It uses numbers to represent letters, symbols, colours, graphics and sounds.

All computers use some variation of the binary numbering system ¹ for representing numbers. Unlike the decimal system, based on the ten digits zero to nine, the binary system has only two digits, zero and one. This system is ideal for computer processing because the ones and zeros can be represented by an electrical on or off.

The computer uses a series of ones and zeros to represent an individual character in a similar manner to that used by morse code. Morse code uses a series of short duration bursts (dots) and long duration bursts (dashes) to represent a character. The bursts may be bursts of electricity, light, smoke or anything else that can be controlled.

One of the most popular ways to represent a character within the computer is to use a seven (ASCII) or eight (EBCDIC) bit code. PC's generally use ASCII while mainframes use EBCDIC.

The ASCII chart, shown in a table in the Numbers Section of the Appendix, gives the various characters and the binary codes which represent them.

An example of character representation is shown by the sentence shown in the right hand column in the table below.

This sentence is a string of alphabet characters to us, but to the computer it represents a string of ones and zeros.

These sets of ones and zeros are binary numbers. Just as the Morse code uses groups of dots and dashes to represent the alphabet, the binary system uses a set of Bits (a single one or zero) to represent each character. If the sentence were saved in memory each character would be saved as one byte in successive memory locations.

1. The binary numbering system is explained in the Appendix.