Many manufacturers devised 8-bit character sets consisting of ASCII plus up to 128 of the unused codes: encodings which covered all the more used Western European (and Latin American) languages, such as Danish, Dutch, French, German, Portuguese, Spanish, Swedish and more could be made.ġ28 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. (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. ![]() When computers and peripherals standardized on eight-bit bytes in the 1970s, 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. Users were not comfortable with any of these compromises and they were often poorly supported. Schemes were also devised so that two letters could be overprinted (often with the backspace control between them) to produce accented letters. 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 Cyrillic or vice versa). Some popular peripherals only implemented a 64-printing-character subset: Teletype Model 33 could not transmit "a" through "z" or five less-common symbols ("`", "". ![]() ![]() Of the 2 7=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. Seven-bit ASCII improved over prior five- and six-bit codes. 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. 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. Early teleprinters were electromechanical, having no microprocessor and just enough electromechanical memory to function.
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