Extended Character Sets

Extended Character Sets

Extended characters are those which are not in the standard ASCII character set, which uses 7-bit characters and thus has values 0 to 127. ASCII Codes 0 to 31 and 127 are non-printing control characters, while codes 32 to 126 match the keys on a US keyboard ("a", "A", etc.).

Using 8 Bits Gives You an Extra 96 Characters

Since computers store characters in 8-bits, many uses have been found for the extra 128 values, most commonly for European characters such as A with Grave accent (À). Actually, only 96 of the codes are used -- values 128 to 159 are not assigned Graphics, just as 0 to 31 are reserved for non-printing control characters.

UNIX Character Sets

UNIX is based on Teletype technology, so it frequently restricts you to 7-bit characters. When UNIX follows the lead of any CRT, it is the DEC VT-100, as in line drawing characters.

DOS Uses All 8-Bits, Some Twice Over

DOS uses the 8-bit IBM PC Extended Character Set (ECS). DOS follows the lead of IBM in using the concept of Code Pages, which provide Graphics for the non-printing control character codes as well (happy faces and other dingbats).

Microsoft Windows 3.1 uses the 8-bit ANSI Character Set, which is incompatible with the DOS character set, but based on the ISO Latin-1 character set. DOS and Windows support Alt-Number for entering extended characters.

To further complicate things, Asian character sets require 16 bits, so Windows NT uses 16-bit Unicode internally for all character values.

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