ASCII Media Works

ASCII ( ), 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. Because of technical limitations of computer systems at the time it was invented, ASCII has just 128 code points, of which only 95 are , which severely limited its scope. All modern computer systems instead use Unicode, which has millions of code points, but the first 128 of these are the same as the ASCII set.

The Internet Assigned Numbers Authority (IANA) prefers the name US-ASCII for this character encoding.

ASCII is one of the IEEE milestones.

Overview

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 in May 1961, 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.

The use of ASCII format for Network Interchange was described in 1969. That document was formally elevated to an Internet Standard in 2015.

Originally based on the (modern) 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, although a few are still commonly used, such as the carriage return, line feed, and tab codes.

For example, lowercase '' i'' would be represented in the ASCII encoding by binary 1101001 = hexadecimal 69 (''i'' is the ninth letter) = decimal 105.

Despite being an American standard, ASCII does not have a code point for the cent (¢). It also does not support English terms with diacritical marks such as résumé and jalapeño, or proper nouns with diacritical marks such as Beyoncé.

History

The 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 later became the United States of America Standards Institute (USASI), and ultimately became 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. There was some debate at the time whether there should be more control characters rather than the lowercase alphabet. The indecision did not last long: during May 1963 the CCITT Working Party on the New Telegraph Alphabet proposed to assign lowercase characters to ''sticks'' 6 and 7,Brief Report: Meeting of CCITT Working Party on the New Telegraph Alphabet, May 13–15, 1963. and International Organization for Standardization TC 97 SC 2 voted during October to incorporate the change into its draft standard.Report of ISO/TC/97/SC 2 – Meeting of October 29–31, 1963. 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'' 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 start of header (SOH)) and moving or removing others (RU was removed). 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 X3.4-1963
* ASA X3.4-1965 (approved, but not published, nevertheless used by IBM 2260 & 2265 Display Stations and IBM 2848 Display Control)
* USAS X3.4-1967
* USAS X3.4-1968
* ANSI X3.4-1977
* ANSI X3.4-1986
* ANSI X3.4-1986 (R1992)
* ANSI X3.4-1986 (R1997)
* ANSI INCITS 4-1986 (R2002)
* ANSI INCITS 4-1986 (R2007)
* (ANSI) INCITS 4-19862012ref name="INCITS_4-1986_R2012"/>
* (ANSI) INCITS 4-19862017ref name="INCITS_4-1986_R2017"/>

In the X3.15 standard, the X3 committee also addressed how ASCII should be transmitted (least significant bit first), 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.

Design considerations

Bit width

The X3.2 subcommittee designed ASCII based on the earlier teleprinter encoding systems. Like other character encodings, ASCII specifies a correspondence between digital bit patterns and character symbols (i.e. graphemes and control characters). This allows digital devices to communicate with each other and to process, store, and communicate character-oriented information such as written language. Before ASCII was developed, the encodings in use included 26 alphabetic characters, 10 numerical digits, and from 11 to 25 special graphic symbols. To include all these, and control characters compatible with the Comité Consultatif International Téléphonique et Télégraphique (CCITT) International Telegraph Alphabet No. 2 (ITA2) standard of 1924, FIELDATA (1956), and early EBCDIC (1963), more than 64 codes were required for ASCII.

ITA2 was in turn based on the 5-bit telegraph code that Émile Baudot invented in 1870 and patented in 1874.

The committee debated the possibility of a shift function (like in ITA2), which would allow more than 64 codes to be represented by a