ISO/IEC 646 - History

History

ISO/IEC 646 and its predecessor ASCII (ANSI X3.4) largely endorsed existing practice regarding character encodings in the telecommunications industry.

As ASCII did not provide a number of characters needed for languages other than English, a number of national variants were made that substituted some less-used characters with needed ones. Due to the incompatibility of the various national variants, an International Reference Version (IRV) of ISO/IEC 646 was introduced, in an attempt to at least restrict the replaced set to the same characters in all variants. The original version (ISO 646 IRV) differed from ASCII only in that in code point 0024, ASCII's dollar sign ($) was replaced by the international currency symbol (¤). The final 1991 version of the code ISO 646:1991 (also known as ITU T.50, International Reference Alphabet or IRA, formerly International Alphabet No. 5, IA5) is identical to ASCII.

The ISO 8859 series of standards governing 8-bit character encodings supersede the ISO 646 international standard and its national variants, by providing 96 additional characters with the additional bit and thus avoiding any substitution of ASCII codes. The ISO 10646 standard, directly related to Unicode, supersedes all of the ISO 646 and ISO 8859 sets with one unified set of character encodings using a larger 21-bit value.

A legacy of ISO/IEC 646 is visible on Windows, where in some fonts or locales, the backslash character used in filenames is rendered as ¥ or other characters. Despite the fact that a different code for ¥ was available even on the original IBM PC, so much text was created with the backslash code used for ¥ that even modern Windows fonts have found it necessary to render the code that way. Another legacy is the existence of trigraphs in the C programming language.