CHARACTERS

Data Representation

Data Representation

Using binary to represent characters

Computers can only process binary numbers (1’s and 0’s) so a system was developed to allow for the use of the full set of alphabetical characters.

It includes both upper and lower case characters, numbers and symbols.

Most commonly used system is called the 7 bit standard ASCII code (American Standard Code for Information Interchange).

Has space for 128 symbols which is enough for standard English.

ASCII

As it only uses 7 bits, it needs an 8 bit byte with the highest bit always stored as zero

Extended ASCII

Standard ASCII only uses the first 128 numbers out of a possible 256.

Other languages need to use the other 128 spaces to include their own special characters so this is called the extended ASCII character set.

There is not one single standard agreed extended code set, there are many including ‘Latin 1 Western European’ which is the default set for Windows, or ‘Latin 2 Central European’.

Character Set

You enter data into a computer by means of an input device such as a keyboard.

Keyboard sends a signal to the computer saying what key has been pressed. This signal is a binary number.

There needs to be a translation between the signal and what appears on the screen. This is the job of the character set.

A character set converts a binary number/code into a written language character.

Unicode

A 1 byte system can only represent 256 symbols which is fine for most languages so ASCII is used.

A 2 byte scheme can represent over 65,000 characters which is enough to hold every used language in the world.

A very popular 2 byte coding standard is called ‘Unicode’. It can handle any language.

The user selects a specific code page which represents a chosen language e.g. code page 1253 represents the Greek language.

ASCII – Binary Character Table