A character in a specified language can be coded as a string of bits (binary digits).

Fixed length codes

5-bit Code

• In the early days, English was the primary language used for communications in most parts of the world.
• The English alphabet consists of 26 letters.
• 5-bits (which can represent 32 symbols) are needed to represent
  (a) upper case characters
  (b) lower case characters
• To represent both cases, a “Shift” character was introduced in some systems.
  Alternatively, one can use higher bit Codes.

6-bit Code

• Some early computers (e.g. ICL1902) use 6-bit code.
• It can represent 64 characters.
• A subset is used for Control.
• The remaining is used for printable characters (letters, numerals, punctuation).

7-bit Code

• ASCII (American Standard Code for Information Interchange)

8-bit Code

• EBCDIC (Extended Binary Coded Decimal Interchange Code)

Character Sets

• With the wide spread use of computer technology, Character sets for the various languages were developed.
• Some languages (notably Chinese) require long bit strings.

Variable Length Codes

• Fixed length coding gave way to Variable length coding.
• The most used characters in a language are represented as one byte and the lesser used characters are represented as two or more bytes.

Unicode

• Unicode aims to have standard character codes for the languages.
• There are formal and informal institutions to help develop, propose and approve new Unicode character sets.
• UTF is a Unicode Transformation Format to transform Unicode characters to fit the specified length (e.g. UTF-8, UTF-16).

Standards and Recommendations

Standards may be

• De Jure (set by law)
• De Facto (set by common usage).

Standards must be followed for Compliance.

Recommendations, which should be followed, can cause variations in the implementations.