Representing Characters - Deyes High School printable pdf download

GCSE Computing A451

Unit 4.3 – Representing Characters

Unit 4.2 – Representing Characters

Candidates should be able to:

a) Explain the use of binary codes to represent characters

b) Explain the term character set

c) Describe with examples (for example ASCII and Unicode) the relationship between

the number of bits per character in a character set and the number of characters

which can be represented.

Representing Characters Using Binary Codes

If a computer is going to store and process any information, it needs to be stored in binary

so that the computer can understand it. So, for a computer to be able to display, store and

process characters (such as uppercase and lowercase letters, numbers, punctuation and

symbols), they need to be stored as binary codes too.

We do this by assigning a unique code to each character. This is called a Code Point. The

code point for each character will be stored as a binary number on your computer.

den

For example, the code point for the letter ‘A’ is 65

. This would be stored as 01000001.

Space

01001001

00100000

01001100

01101111

01110110

01100101

00100000

01000010

01101001

01101110

01100001

01110010

01111001

00100001

The most commonly used system is called the 7 bit standard ASCII (American Standard Code

for Information Interchange) code. This can be used to represent 128 different symbols,

which is enough for use in standard English, but not enough for other languages (for

instance, many European languages require separate characters for vowels with accents

etc...).

Of course 7 bits is not a convenient package for a computer, so the code is stored as an 8 bit

byte with the highest bit set to zero. This means that standard ASCII only uses the first 128

numbers available out of a possible 256.

Extended ASCII sets make use of the remaining 128 codes to represent special characters in

other languages, such as umlauts and accents. There isn’t a single standard agreed extended

ASCII code set and there are many of them, as various countries wanted to use the higher

bits for their own alphabets.

Representing Characters - Deyes High School

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