ISO/IEC 646

The international standard ISO 646 defines the so-called International Alphabet No. 5 ( International Alphabet No. 5, IA5 ), a character set for the transmission and storage of data. It corresponds largely to the character set (US- ) ASCII.

History

IA5 1963 was adopted by the ISO as standard IS 646 and at the same time as CCITT Recommendation V.3. The CCITT has recommended V.3 in 1984, revised and re- adopted as T.50. T.50 received in 1992 a revision where the character set was then called the International Reference Alphabet (IRA ). IA1 is the Morse alphabet, IA2, the encoded in 5 bits character set of teletypes.

For the national versions of 12 positions in the character set of nationally defined characters are released. The German version is specified in DIN 66003 and is registered as variant 21; it uses eight national positions for the paragraph sign, large and small umlauts and the ß. These characters replace, for example, brackets and braces of ASCII. US-ASCII is according to the standard, the national version of No. 6, but in practice is US-ASCII, the international version, because of their support from the computer manufacturer in the world. The official international version is almost never used does not include the dollar sign, since the Soviet Union would have otherwise refused to agree to the standard.

Not all national variants obtained the same distribution; the Dutch variant approximately contains no characters that are absolutely necessary for printing Dutch texts, which is why most computers sold in the Netherlands used the unmodified ASCII character set and a U.S. keyboard layout.

The national versions in ISO 646 were detached from the 1980s, in practice, by the de facto standard of 8- bit MS- DOS code pages of the IBM PC and the also achtbittigen ISO -8859 character sets - the latter are z. example, in Linux and Microsoft Windows. All of these standards are based unlike national versions of ISO 646 on the unchanged ASCII character set. The characters are additionally required not replace longer - ASCII characters, but can be added to these. Consequently the interchangeability of data between computers of different countries has been simplified; also for programmers outside the U.S., life became easier, as many of the ISO 646 standard for replacing the shared characters of US-ASCII, the yes thus partially or completely absent in the other ISO -646 variants, common in many programming languages occur.

ISO 646 forms ( e) are the basis for the character encoding of the video text.

Note the relationship of the numbers of the standards ISO 646 for the IA5 and ISO 10646 for UCS or Unicode.

Construction

IA5 largely corresponds to U.S. ASCII, but also serves as an IRV ( International Reference Version) for standardized national variants of the IA5. These national variations were often used on older computer systems (pre- PC ) to represent German umlauts for example. ISO 646 was present, for example, on the Apple IIe and in CP / M computers, the usual method of non-English characters.

Each character or control characters in IA5 is exactly encoded as ASCII 7- bit. The character set includes uppercase and lowercase letters, numbers, punctuation, and in the lower 32 digits characters for controlling data communication or output devices.