Extended ASCII

Extended ASCII (EASCII or high ASCII) character encodings are eight-bit or larger encodings that include the standard seven-bit ASCII characters, plus additional characters. Using the term 'extended ASCII' on its own is sometimes criticized, because it can be mistakenly interpreted to mean that the ASCII standard has been updated to include more than 128 characters or that the term unambiguously identifies a single encoding, neither of which is the case. Extended ASCII (EASCII or high ASCII) character encodings are eight-bit or larger encodings that include the standard seven-bit ASCII characters, plus additional characters. Using the term 'extended ASCII' on its own is sometimes criticized, because it can be mistakenly interpreted to mean that the ASCII standard has been updated to include more than 128 characters or that the term unambiguously identifies a single encoding, neither of which is the case. There are many extended ASCII encodings (more than 220 DOS and Windows codepages). EBCDIC ('the other' major 8-bit character code) likewise developed many extended variants (more than 186 EBCDIC codepages) over the decades. ASCII was designed in the 1960s for teleprinters and telegraphy, and some computing. Early teleprinters were electromechanical, having no microprocessor and just enough electromechanical memory to function. They fully processed one character at a time, returning to an idle state immediately afterward, this meant that any control sequences had to be only one character long, and thus a large number of codes needed to be reserved for such controls. They were typewriter-derived impact printers, and could only print a fixed set of glyphs, which were cast into a metal type element or elements; this also encouraged a minimum set of glyphs. Seven-bit ASCII improved over prior five- and six-bit codes. Of the 27=128 codes, 33 were used for controls, and 95 carefully selected printable characters (94 glyphs and one space), which include the English alphabet (uppercase and lowercase), digits, and 31 punctuation marks and symbols: all of the symbols on a standard US typewriter plus a few selected for programming tasks. Some popular peripherals only implemented a 64-printing-character subset: Teletype Model 33 could not transmit 'a' through 'z' or five less-common symbols ('`', '{', '|', '}', and '~'). and when they received such characters they instead printed 'A' through 'Z' (forced all caps) and five other mostly-similar symbols ('@', '', and '^'). The ASCII character set is barely large enough for US English use and lacks many glyphs common in typesetting, and far too small for universal use. Many more letters and symbols are desirable, useful, or required to directly represent letters of alphabets other than English, more kinds of punctuation and spacing, more mathematical operators and symbols (× ÷ ⋅ ≠ ≥ ≈ π etc.), some unique symbols used by some programming languages, ideograms, logograms, box-drawing characters, etc. For years, applications were designed around the 64-character set and/or the 95-character set, so several characters acquired new uses. For example, ASCII lacks '÷', so most programming languages use '/' to indicate division. The biggest problem for computer users around the world was other alphabets. ASCII's English alphabet almost accommodates European languages, if accented letters are replaced by non-accented letters or two-character approximations. Modified variants of 7-bit ASCII appeared promptly, trading some lesser-used symbols for highly desired symbols or letters, such as replacing '#' with '£' on UK Teletypes, '' with '¥' in Japan or '₩' in Korea, etc. At least 29 variant sets resulted. 12 code points were modified by at least one modified set, leaving only 82 'invariant' codes. Programming languages however had assigned meaning to many of the replaced characters, work-arounds were devised such as C three-character sequences '??(' and '??)' to represent '{' and '}'. Languages with dissimilar basic alphabets could use transliteration, such as replacing all the Latin letters with the closest match Cyrillic letters (resulting in odd but somewhat readable text when English was printed in Cryllic or vice-versa). Schemes were also devised so that two letters could be overprinted (often with the backspace control between them) to produce accented letters. Users were not comfortable with any of these compromises and they were often poorly supported. When computers and peripherals standardized on eight-bit bytes in the 1970's, it became obvious that computers and software could handle text that uses 256-character sets at almost no additional cost in programming, and no additional cost for storage. (Assuming that the unused 8th bit of each byte was not reused in some way, such as error checking, Boolean fields, or packing 8 characters into 7 bytes.) This would allow ASCII to be used unchanged and provide 128 more characters. Many manufacturers devised 8-bit character sets consisting of ASCII plus up to 128 of the unused codes. Since Eastern Europe were politically separated at the time, 8-bit encodings which covered all the more used European (and Latin American) languages, such as Danish, Dutch, French, German, Portuguese, Spanish, Swedish and more could be made, often called 'Latin' or 'Roman'. 128 additional characters is still not enough to cover all purposes, all languages, or even all European languages, so the emergence of many proprietary and national ASCII-derived 8-bit character sets was inevitable. Translating between these sets (transcoding) is complex (especially if a character is not in both sets); and was often not done, producing mojibake (semi-readable resulting text, often users learned how to manually decode it). There were eventually attempts at cooperation or coordination by national and international standards bodies in the late 1990's, but manufacture proprietary sets remained the most popular by far, primarily because the standards excluded many popular characters. Various proprietary modifications and extensions of ASCII appeared on non-EBCDIC mainframe computers and minicomputers, especially in universities.