ISO/IEC 646

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ISO 646 is an ISO standard that specifies a 7-bit character code from which several national standards are derived, the best known of which is ASCII. Since the portion of ISO 646 shared by all countries specified only the letters used in the English alphabet, other countries using the Latin alphabet with extensions needed to create national variants of ISO 646 to be able to use their native languages. Since universal acceptance of the 8 bit byte did not exist at that time, the national characters had to be made to fit within the constraints of 7 bits, meaning that some characters that appear in ASCII do not appear in other national variants of ISO 646.

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[edit] History

ISO/IEC 646 and its predecessor ASCII, ANSI X3.4, largely endorses existing practice regarding character encodings in the telecommunications industry's network

During the 1960s, there was debate regarding whether character encoding standards (at either the national or international levels) for computers should follow 1) existing practice in the telecommunications industry (which was largely paper-tape based, but which was commonly transmitted on-line digitally over wires) or, conversely, 2) existing practice in the punched-card portion of the computer industry, whose heritage was especially the off-line storage of World War II-era electro-mechanical punched-card machines predating electronic computers. For obvious corporate-history reasons regarding Hollerith punched cards, IBM sided with the punched-card character encodings, embodied by EBCDIC, whereas many other computer manufacturers sided with the telecommunications industry's character encodings.

The ISO 8859 series of standards governing 8-bit character encodings supersede the ISO 646 international standard and its national variants. The ISO 10646 standard, directly related to Unicode, supersedes all of ISO 646's and ISO 8859's sets of national-variant character encodings with arguably one unified set of character encodings.

[edit] National variants

Some national variants of ISO 646 are:

Code ISO-
IR		 Standard Used in
CA-1 121 CSA Z243.4-1985 Canada (nr. 1 alternative, with “î”)
(French, classical)
CA-2 122 CSA Z243.4-1985 Canada (nr. 2 alternative, with “É”)
(French, reformed orthography)
CN 057 GB/T 1988-80 People's Republic of China (Basic Latin)
CU 151 NC 99-10:81 Cuba (Spanish)
DE 021 DIN 66083 Germany (German)
DK — DS 2089 Denmark (Danish)
FR 069 AFNOR NF Z 62010-1982 France (French)
FR-0 025 AFNOR NF Z 62010-1973 France (obsolete since April 1985)
GB 004 BSI 4730 United Kingdom (English)
GR 088 HOS ELOT Greece (obsolete)
HU 086 MSZ 7795/3 Hungary(Hungarian)
IE 207 NSAI 433:1996 Ireland (Irish Goidelic)
 
Code ISO-
IR		 Standard Used in
INV — ISO 646:1983 international (Invariant subset)
IRV 002 ISO 646:1983 International Reference Variant
JA 014 JIS C 6220-1969 Japan (Romaji)
JA-O 092 JIS C 6229-1984 Japan (OCR-B)
KR — ? South Korea
MT — ? Malta (Maltese, English)
NO 060 NS 4551 version 1 Norway
NO-2 061 NS 4551 version 2 Norway (obsolete since June 1987)
SE 010 SEN 85 02 00 Annex B Sweden (basic Swedish)
SE-C 011 SEN 85 02 00 Annex C Sweden (extended Swedish for names)
T.61 102 ITU/CCITT T.61 Recommendation International (Teletex)
US 006 ANSI X3.4-1968 United States (ASCII)
YU 141 JUS I.B1.002 former Yugoslavia (Croatian, Slovenian, Serbian, Latin)

Other proprietary standards approved later for international use by some standard committees:

Code ISO-
IR		 Approved by Origin Used in
ES 085 ECMA IBM Spain (Basque, Castilian, Catalan, Galician)
esp 017 ECMA Olivetti Spanish (international)
DK-SE 009-1 SSK NATS, main set Sweden and Denmark (journalistic texts)
FI-SE 008-1 SSK NATS, main set Sweden and Finland (journalistic texts)
 
Code ISO-
IR		 Approved by Origin Used in
ita 015 ECMA Olivetti Italian
PT 084 ECMA IBM Portugal (Portuguese, Spanish)
por 016 ECMA Olivetti Portuguese (international)

The specifics of the changes for some of these variants are given in this table:

Codes Characters for each ISO 646 compatible charset
binary decimal hexa INV US T.61 JA JA-O CN IRV GB DK NO NO-2 SE SE-C DE HU FR FR-0 CA-1 CA-2 IE IS ita por PT esp ES CU MT YU
010 0010 34 22 " " " " " " " " " " " " " " " " " " " " " " " " " " " " "
010 0011 35 23   # # # # # # £ # # § # # # # £ £ # # £ # £ # £ # # # # #
010 0100 36 24   $ ¤ $ $ ¥ $ $ $ $ $ ¤ ¤ $ ¤ $ $ $ $ $ $ $ $ $ $ $ ¤ $ $
010 1001 39 27 ' ' ' ' ' ' ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’
010 1100 44 2C , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,
010 1101 45 2D - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
010 1111 47 2F / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
100 0000 64 40   @ @ @ @ @ @ @ @ @ @ @ É § Á à à à à Ó Ð § § ´ § · @ @ Ž
101 1011 91 5B   [ [ [ [ [ [ [ Æ Æ Æ Ä Ä Ä É ° ° â â É Þ ° Ã Ã ¡ ¡ ¡ ġ Š
101 1100 92 5C   \   ¥ ¥ \ \ \ Ø Ø Ø Ö Ö Ö Ö ç ç ç ç Í \ ç Ç Ç Ñ Ñ Ñ ż Đ
101 1101 93 5D   ] ] ] ] ] ] ] Å Å Å Å Å Ü Ü § § ê ê Ú Æ é Õ Õ ¿ Ç ] ħ Ć
101 1110 94 5E   ^   ^ ^ ^ ˆ ˆ ˆ ˆ ˆ ˆ Ü ˆ ˆ ^ ˆ î É Á Ö ˆ ˆ ˆ ˆ ¿ ¿ ˆ Č
101 1111 95 5F _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
110 0000 96 60   `   `   ` ` ` ` ` ` ` é ` á µ µ ô ô ó ð ù ` ` ` ` ` ċ ž
111 1011 123 7B   {   { { { { { æ æ æ ä ä ä é é é é é é þ à ã ã ° ´ ´ Ġ š
111 1100 124 7C   | | | | | | | ø ø ø ö ö ö ö ù ù ù ù í | ò ç ç ñ ñ ñ Ż đ
111 1101 125 7D   }   } } } } } å å å å å ü ü è è è è ú æ è õ õ ç ç [ Ħ ć
111 1110 126 7E   ~   ‾   ~ ˜ ˜ ˜ ¯ | ˜ ü ß ˝ ¨ ¨ û û á ö ì ° ˜ ˜ ¨ ¨ Ċ č

In the table above, the cells with non-white background emphasize the differences from the US variant used in the Basic Latin subset of ISO/IEC 10646 and Unicode.

The characters displayed in cells with red background could be used as combining diacritics, when preceded or followed with a backspace C0 control (this encoding method is deprecated or is not recommended as it was part of some withdrawn national standards). Without such complex encoding, they are no different from the symbols used in the US variant (although glyph variants are still possible, especially on the quotation marks, and circumflex or tilde symbols).

Later, when 8 bit character sets gained more acceptance, ISO 8859-1, ISO 8859-2, and ISO 8859-3 became the preferred method of coding most of these variants.

[edit] Variants of ASCII that are not ISO 646

There are also some 7-bit character sets that are not officially part of the ISO 646 standard. Examples include:

  • 7-bit Greek, ELOT 927. The Greek alphabet is mapped to positions 0x61–0x71 and 0x73–0x79, on top of the Latin lowercase letters. This mapping with the high bit set is ISO 8859-7.
  • 7-bit Cyrillic, KOI-7 or Short KOI. The Cyrillic characters are mapped to positions 0x60–0x7E, on top of the Latin lowercase letters. Superseded by the KOI-8 variants.
  • 7-bit Hebrew, SI 960. The Hebrew alphabet is mapped to positions 0x60–0x7A, on top of the lowercase Latin letters (and grave accent for aleph). 7-bit Hebrew was always stored in visual order. This mapping with the high bit set, i.e. with the Hebrew letters in 0xE0–0xFA, is ISO 8859-8.
  • 7-bit Arabic, ASMO 449. The Arabic alphabet is mapped to positions 0x41–0x5A and 0x60–0x6A, on top of both uppercase and lowercase Latin letters. This mapping with the high bit set is ISO 8859-6.

[edit] See also

[edit] External links

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