ASCII

The American Standard Code for Information Interchange (ASCII) is a 7-bit character-encoding scheme for the Western lower- and uppercase letters (letters without accents only), digits, and punctuation marks. In addition it defines 33 control characters (see Table 1), many of which are obsolete. In total ASCII has space for 27 = 128 codes. The ASCII codes from 32 to 126 represent printable characters in binary form (see Table 2), such as are used in computers, telecommunication equipment, and other electronic and mechanical devices. The last ASCII code (127) is DEL(ete) (111&thinsp;1111) that, being in the last position, has all bits up. Although a control character, it is last in the ASCII table for the historic reason that it enabled the rubout of an incorrect 7-bit paper-tape character (7 holes in the tape) without requiring a complete copy of the tape.

Historically, ASCII developed from telegraph codes. Work on the ASCII standard formally began on October 6, 1960, with the first meeting of the American Standards Association's (ASA) X3.2 subcommittee. The first edition of the standard was published in 1963, a major revision (1967) included the the lowercase letters, and the most recent update was in 1986.

The order of the printable characters in ASCII is such that alphabetic sorting coincides to a large extent with numeric sorting.

As stated, many of the control characters are obsolete. However, ASCII 9 (tab stop), ASCII 10 (line feed), and ASCII 13 (carriage return) are still in common use. The tab character has the same function as on typewriters and lets the cursor jump from tab stop to tab stop. The pair ASCII 13 and ASCII 10 is used under MS-Windows to indicate end of line ("hard return"), whereas under Unix type operating systems only linefeed (ASCII 10) is used to give a hard return.

Later encoding standards, such as ISO 8859, ANSI 1252 and Unicode UTF-8, are compatible with ASCII, that is, their codes for the first 128 characters are identical to the ASCII codes.

