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ISO 646 is an ISO standard that specifies a 7-bit character code from which several national standards are derived, the best known of which is ASCII. Since the portion of ISO 646 shared by all countries specified only the letters used in the English alphabet, other countries using the Latin alphabet with extensions needed to create national variants of ISO 646 to be able to use their native languages. Since universal acceptance of the 8 bit byte did not exist at that time, the national characters had to be made to fit within the constraints of 7 bits, meaning that some characters that appear in ASCII do not appear in other national variants of ISO 646.
History ISO/IEC 646 and its predecessor ASCII, ANSI X3.4, largely endorses existing practice regarding character encodings in the telecommunications industry's network During the 1960s, there was debate regarding whether character encoding standards (at either the national or international levels) for computers should follow 1) existing practice in the telecommunications industry (which was largely paper-tape based, but which was commonly transmitted on-line digitally over wires) or, conversely, 2) existing practice in the punched-card portion of the computer industry, whose heritage was especially the off-line storage of World War II-era electro-mechanical punched-card machines predating electronic computers. For obvious corporate-history reasons regarding Hollerith punched cards, IBM sided with the punched-card character encodings, embodied by EBCDIC, whereas many other computer manufacturers sided with the telecommunications industry's character encodings. The ISO 8859 series of standards governing 8-bit character encodings supersede the ISO 646 international standard and its national variants. The ISO 10646 standard, directly related to Unicode, supersedes all of ISO 646's and ISO 8859's sets of national-variant character encodings with arguably one unified set of character encodings. National variants Some national variants of ISO 646 are: Other proprietary standards approved later for international use by some standard committees: The specifics of the changes for some of these variants are given in this table: In the table above, the cells with non-white background emphasize the differences from the US variant used in the Basic Latin subset of ISO/IEC 10646 and Unicode. The characters displayed in cells with red background could be used as combining diacritics, when preceded or followed with a backspace C0 control (this encoding method is deprecated or no more recommanded as it was part of some withdrawn national standards). Without such complex encoding, they are not different from the symbol used in the US variant (although glyph variants are still possible, especially on the quotation marks, and circumflex or tilde symbols). Later, when 8 bit character sets gained more acceptance, ISO 8859-1, ISO 8859-2, and ISO 8859-3 became the preferred method of coding most of these variants. Variants of ASCII that are not ISO 646 There are also some 7-bit character sets that are not officially part of the ISO 646 standard. Examples include: See also | ||||||||
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