ASCII( American Standard Code for Information Interchange)

ASCII  abbreviated from American Standard Code for Information Interchange, is a character encoding standard (the Internet Assigned Numbers Authority (IANA) prefers the name US-ASCII). ASCII codes represent text in computers, telecommunications equipment, and other devices. Most modern character-encoding schemes are based on ASCII, although they support many additional characters.

ASCII was developed from telegraph code. Its first commercial use was as a seven-bit teleprinter code promoted by Bell data services. Work on the ASCII standard began on October 6, 1960, with the first meeting of the American Standards Association’s (ASA) (now the American National Standards Institute or ANSI) X3.2 subcommittee. The first edition of the standard was published in 1963, underwent a major revision during 1967, and experienced its most recent update during 1986. Compared to earlier telegraph codes, the proposed Bell code and ASCII were both ordered for more convenient sorting (i.e., alphabetization) of lists, and added features for devices other than teleprinters.

Originally based on the English alphabet, ASCII encodes 128 specified characters into seven-bit integers as shown by the ASCII chart above. The characters encoded are numbers 0 to 9, lowercase letters a to z, uppercase letters A to Z, basic punctuation symbols, control codes that originated with Teletype machines, and a space. For example, lowercase j would become binary 1101010 and decimal 106. ASCII includes definitions for 128 characters: 33 are non-printing control characters (many now obsolete) that affect how text and space are processed and 95 printable characters, including the space (which is considered an invisible graphic).

A June 1992 RFC and the Internet Assigned Numbers Authority registry of character sets recognize the following case-insensitive aliases for ASCII as suitable for use on the Internet: ANSI_X3.4-1968  (canonical name), iso-ir-6, ANSI_X3.4-1986, ISO_646.irv:1991, ASCII, ISO646-US, US-ASCII (preferred MIME name), us, IBM367, cp367, and csASCII.

Of these, the IANA encourages use of the name “US-ASCII” for Internet uses of ASCII (even if it is a redundant acronym, but the US is needed because of regular confusion of the ASCII term with other 8 bit based character encoding schemes such as Extended ASCII or UTF-8 for example). One often finds this in the optional “charset” parameter in the Content-Type header of some MIME messages, in the equivalent “meta” element of some HTML documents, and in the encoding declaration part of the prologue of some XML documents.





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