ASCII

ASCII (American Standard Code for Information Interchange) is a one byte code used to represent characters. Standard ASCII uses the low 7 bits and can represent 128 (2^7) characters. More on ASCII.

The first 32 characters (00-1F hex )are not printable - they are control characters. There are 96 printable characters.


UTF-8 (8-bit UCS/Unicode Transformation Format) is a variable-length character encoding for Unicode. It is able to represent any character in the Unicode standard, yet is backwards compatible with ASCII.

ASCII Encoding Example:
The hex value for the letter 'D' is 44. In decimal 'D' is 68 (4x16 + 4x1)
In binary, it is 01000100.

Extended ASCII character set, high bit (bit 7) set to one.   (click on picture to see another version of table)

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Unicode

Unicode Reference

As the need to represent more characters (Chinese, Thai, Japanese) increases, we need a larger code space. This is why ASCII is being replaced by Unicode. Unicode uses 16 bits which means it can represent 2^16 = 65,536 different characters.

32 bit codes are also being developed which would allow over 4 billion characters to be represented.

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Reference: Brief History of Character Codes ...

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