Re: ASCII as a subset of Unicode

From: Jim Allan (
Date: Sat Apr 11 2009 - 13:48:41 CDT

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    Jukka K. Korpela wrote:
    > I'm not sure what you mean by "such" here, but in fact, even in the
    > 1980s and early 1990s, DECsystem-10 and -20 (PDP-10 and -20) used a
    > word length of 36 bits, packing five 7-bit ASCII characters in one
    > word (and using the spare bit for special purposes).
    > ASCII was surely designed to allow implementations where 7 bits are
    > used for one character. Don't confuse this with the current situation
    > where such implementations are obsolete and "everyone" uses at least 8
    > bits for a character, even when working with ASCII only.

     From :

    "It was therefore decided to use 7 bits to store the new ASCII code,
    with the eighth bit being used as a parity bit to detect transmission

     From :

    "ASCII uses only 7 bits and allows the most significant eighth bit to be
    used as parity bit, highlight bit, end-of-string bit (all of which are
    considered bad practice nowadays) or to include additional characters
    for internationalization <>
    (i18n for which we need 8bit-clean programs that do none of
    afore-mentioned silly tricks) but ASCII defined no standard
    <> for this and many
    manufacturers invented their own proprietary codepages

    For an original ASCII definition see
    > :

    "This character set is the first of a family of sets. Higher-order sets
    will enlarge the repertoire for both 'graphics' and 'controls'."

    Though not defined in the original standard, from the beginning it was
    understood that ASCII would normally run in an 8-bit environment and
    that the 8th bit could be used to define additional characters, and that
    the standards committee expected to define higher-order sets.

    Jim Allan

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