- Explain the use of binary codes to represent characters
- Explain the term, 'character set‘
- 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.

Uses codes to represent a character, number or symbol in the language.

Number of bits represents limit of how many characters can be represented.
Character sets

Coverts binary or code into a written language character.

The keyboard sends a signal telling the computer which key has been pressed, e.g. the 5 th on bottom row has been pressed.

This means you can sometimes use the same keyboard for different languages, the European keyboard can produce Latin from the Latin Alphabet No 1 character set.
ASCII
7 bit

Most common system is 7 bit standard ASCII, with 128 spaces for symbols it can represent the
English language.

7 bits is not ideal for computers si it is stored as 1 byte just with the highest bit left as 0.

Every character is represented by a binary number, e.g. 01101101.

Upper case A: 01000001.

Lower case a: 01100001.

Every letter takes a byte of storage.
Extended

Still a byte of storage but uses the highest bit to store an extra 128 different characters, giving
256 in total.

This is useful for some languages that have more symbols than English.

There is not a set extended ASCII code yet that is agreed by everyone as countries need enough storage for their alphabet.
Unicode

For some languages, e.g. far-east languages, many more characters are needed than 8 bits from extended ASCII can supply.

A 2 byte system can represent 65,535 characters, enough to have all the languages of the world in one place.


Means that manufactures can sell one computer to all over the world, so their customers just select their language when they first use the computer.

Unicode is a 2 byte character set, it can handle any language and uses ‘code pages’ which is one section of the total space, a code page represents the selected language, e.g. Grrek is page 1253.
Explain how binary codes are used to represent characters on our keyboards
A binary number represents one character in a language, when a key is pressed, the keyboard send a signal telling the computer, the computer compares the binary number with the character set and outputs the relevant character.
What is the ASCII code for d and K? d = 100 = 01100100
K = 75 = 01001011
What is a character set?
A set of characters, with corresponding binary values, it is recognised by the hardware and software in a computer and is commonly used to represent languages.
Describe the relationship between number of bits and the range of characters the computer can use.
The more bits, the more characters that can be stored because there is a higher range of binary numbers to use to represent characters. 7 bit ASCII can only represent 128 characters whereas the 2 byte (16 bit)
Unicode can represent 65535 characters.