Character Encoding (Cambridge (CIE) A Level Computer Science) : Revision Note

Character sets

What is a character set?

• A character set is all the characters and symbols that can be represented by a computer system

• Each character is given a unique binary code

• Character sets are ordered logically, the code for ‘B’ is one more than the code for ‘A’

• A character set provides a standard for computers to communicate and send/receive information

• Without a character set, one system might interpret 01000001 differently from another

• The number of characters that can be represented is determined by the number of bits used by the character set

• Two common character sets are:

  • American Standard Code for Information Interchange (ASCII)

  • Universal Character Encoding (UNICODE)

ASCII

What is ASCII?

• ASCII is a character set and was an accepted standard for information interchange

• ASCII uses 7 bits, providing 2⁷ unique codes (128) or a maximum of 128 characters it can represent

• This is enough to represent the letters, numbers, and symbols from a standard keyboard

• The sixth bit changes from 1 to 0 when comparing uppercase and lowercase characters

  • a 0110 0001

  • A 0100 0001

  • b 0110 0010

  • B 0100 0010

• This made conversion between the two much easier

• This speeds up the overall usability of the character set

• ASCII only represents basic characters needed for English, limiting its use for other languages

Extended ASCII

What is extended ASCII?

• Extended ASCII uses an 8th bit, providing 256 unique codes (2⁸ = 256) or a maximum of 256 characters it can represent

• Extended ASCII provides essential characters such as mathematical operators and more recent symbols such as ©

• This allows for non-English characters and for drawing characters to be included

UNICODE

What is UNICODE?

• UNICODE is a character set and was created as a solution to the limitations of ASCII

• UNICODE uses a minimum of 16 bits, providing 2¹⁶  unique codes (65,536) or a minimum of 65,536 characters it can represent

• UNICODE can represent characters from all the major languages around the world

• UNICODE was designed to create a universal standard that covered all languages and all writing systems

• The first 128 characters in the UNICODE character set are the same as ASCII

ASCII vs UNICODE