ASCII (/’?ski/ ( listen) ASS-kee),:6 abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. 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 is the traditional name for the encoding system; the Internet Assigned Numbers Authority (IANA) prefers the updated name US-ASCII, which clarifies that this system was developed in the US and based on the typographical symbols predominantly in use there.ASCII is one of a 1963 List of IEEE milestones.ASCII chart from an earlier-than 1972 printer manual (b1 is the least significant bit.)
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.
Ninety-five of the encoded characters are printable: these include the digits 0 to 9, lowercase letters a to z, uppercase letters A to Z, and punctuation symbols. In addition, the original ASCII specification included 33 non-printing control codes which originated with Teletype machines; most of these are now obsolete.For example, lowercase i would be represented in the ASCII encoding by binary 1101001 = hexadecimal 69 (i is the ninth letter) = decimal 105. HistoryThe American Standard Code for Information Interchange (ASCII) was developed under the auspices of a committee of the American Standards Association (ASA), called the X3 committee, by its X3.2 (later X3L2) subcommittee, and later by that subcommittee’s X3.2.4 working group (now INCITS).
The ASA became the United States of America Standards Institute (USASI):211 and ultimately the American National Standards Institute (ANSI). With the other special characters and control codes filled in, ASCII was published as ASA X3.4-1963, leaving 28 code positions without any assigned meaning, reserved for future standardization, and one unassigned control code.:66, 245 There was some debate at the time whether there should be more control characters rather than the lowercase alphabet.:435 The indecision did not last long: during May 1963 the CCITT Working Party on the New Telegraph Alphabet proposed to assign lower case characters to sticks[a] 6 and 7, and International Organization for Standardization TC 97 SC 2 voted during October to incorporate the change into its draft standard. The X3.2.4 task group voted its approval for the change to ASCII at its May 1963 meeting. Locating the lowercase letters in sticks[a] 6 and 7 caused the characters to differ in bit pattern from the upper case by a single bit, which simplified case-insensitive character matching and the construction of keyboards and printers. The X3 committee made other changes, including other new characters (the brace and vertical bar characters), renaming some control characters (SOM became the start of header (SOH)) and moving or removing others (RU was removed).:247–248 ASCII was subsequently updated as USAS X3.4-1967, then USAS X3.4-1968, ANSI X3.4-1977, and finally, ANSI X3.4-1986.
Revisions of the ASCII standard:ASA X3.4-1963ASA X3.4-1965 (approved, but not published, nevertheless used by IBM 2260 & 2265 Display Stations and IBM 2848 Display Control):423, 425–428, 435–439USAS X3.4-1967USAS X3.4-1968ANSI X3.4-1977ANSI X3.4-1986ANSI X3.4-1986 (R1992)ANSI X3.4-1986 (R1997)ANSI INCITS 4-1986 (R2002)ANSI INCITS 4-1986 (R2007)ANSI INCITS 4-1986 (R2012)In the X3.15 standard, the X3 committee also addressed how ASCII should be transmitted (least significant bit first),:249–253 and how it should be recorded on perforated tape. They proposed a 9-track standard for magnetic tape and attempted to deal with some punched card formats.