ISO/IEC 646

This article is about a character encoding standard. For the ISO C header file, see iso646.h.

ISO/IEC 646:1991, Information technology — ISO 7-bit coded character set for information interchange, is an ISO standard that since its first edition in 1972 has specified a 7-bit character code from which several national standards are derived. ISO/IEC 646 was also ratified by ECMA as ECMA-6.

Since the portion of ISO/IEC 646 shared by all countries (the "invariant set") specified only those letters used in the basic modern Latin alphabet, other countries using the Latin alphabet with extensions needed to create national variants of ISO 646 to be able to use their native scripts. 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.

History

ISO/IEC 646 and its predecessor ASCII (ANSI X3.4) largely endorsed existing practice regarding character encodings in the telecommunications industry.

As ASCII did not provide a number of characters needed for languages other than English, a number of national variants were made that substituted some less-used characters with needed ones. Due to the incompatibility of the various national variants, an International Reference Version (IRV) of ISO/IEC 646 was introduced, in an attempt to at least restrict the replaced set to the same characters in all variants. The original version (ISO 646 IRV) differed from ASCII only in that in code point 0024, ASCII's dollar sign ($) was replaced by the international currency symbol (¤). The final 1991 version of the code is identical to ASCII.^[1]

The ISO 8859 series of standards governing 8-bit character encodings supersede the ISO 646 international standard and its national variants, by providing 96 additional characters with the additional bit and thus avoiding any substitution of ASCII codes. The ISO 10646 standard, directly related to Unicode, supersedes all of the ISO 646 and ISO 8859 sets with one unified set of character encodings using a larger 21-bit value.

A legacy of ISO/IEC 646 is visible on Windows, where in some fonts or locales, the backslash character used in filenames is rendered as ¥ or other characters. Despite the fact that a different code for ¥ was available even on the original IBM PC, so much text was created with the backslash code used for ¥ that even modern Windows fonts have found it necessary to render the code that way. Another legacy is the existence of trigraphs in the C programming language.

Codepage layout

The following table shows the ISO/IEC 646 character set. Each character is shown with the hex code of its Unicode equivalent and the decimal value of the ISO/IEC 646 code. Grey shaded cells indicate code points with character glyphs that vary from region to region. These are discussed in detail below.

ISO/IEC 646
	−0	−1	−2	−3	−4	−5	−6	−7	−8	−9	−A	−B	−C	−D	−E	−F
0−	NUL 0000 0	SOH 0001 1	STX 0002 2	ETX 0003 3	EOT 0004 4	ENQ 0005 5	ACK 0006 6	BEL 0007 7	BS 0008 8	HT 0009 9	LF 000A 10	VT 000B 11	FF 000C 12	CR 000D 13	SO 000E 14	SI 000F 15
1−	DLE 0010 16	DC1 0011 17	DC2 0012 18	DC3 0013 19	DC4 0014 20	NAK 0015 21	SYN 0016 22	ETB 0017 23	CAN 0018 24	EM 0019 25	SUB 001A 26	ESC 001B 27	FS 001C 28	GS 001D 29	RS 001E 30	US 001F 31
2−	SP 0020 32	! 0021 33	" 0022 34	35	36	% 0025 37	& 0026 38	' 0027 39	( 0028 40	) 0029 41	* 002A 42	+ 002B 43	, 002C 44	- 002D 45	. 002E 46	/ 002F 47
3−	0 0030 48	1 0031 49	2 0032 50	3 0033 51	4 0034 52	5 0035 53	6 0036 54	7 0037 55	8 0038 56	9 0039 57	: 003A 58	; 003B 59	< 003C 60	= 003D 61	> 003E 62	? 003F 63
4−	64	A 0041 65	B 0042 66	C 0043 67	D 0044 68	E 0045 69	F 0046 70	G 0047 71	H 0048 72	I 0049 73	J 004A 74	K 004B 75	L 004C 76	M 004D 77	N 004E 78	O 004F 79
5−	P 0050 80	Q 0051 81	R 0052 82	S 0053 83	T 0054 84	U 0055 85	V 0056 86	W 0057 87	X 0058 88	Y 0059 89	Z 005A 90	91	92	93	94	_ 005F 95
6−	96	a 0061 97	b 0062 98	c 0063 99	d 0064 100	e 0065 101	f 0066 102	g 0067 103	h 0068 104	i 0069 105	j 006A 106	k 006B 107	l 006C 108	m 006D 109	n 006E 110	o 006F 111
7−	p 0070 112	q 0071 113	r 0072 114	s 0073 115	t 0074 116	u 0075 117	v 0076 118	w 0077 119	x 0078 120	y 0079 121	z 007A 122	123	124	125	126	DEL 007F 127

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 66003 Germany (German) DK — DS 2089 Denmark (Danish) FI 010 SFS 4017 Finland (basic version) FR 069 AFNOR NF Z 62010-1982 France (French) FR-0 025 AFNOR NF Z 62010-1973 France (obsolete since April 1985) GB 004 BS 4730 United Kingdom (English) GR 088 HOS ELOT Greece (obsolete) HU 086 MSZ 7795/3 Hungary (Hungarian) IE 207 NSAI 433:1996 Ireland (Irish)

Code ISO- IR Standard Used in INV 170 ISO 646:1983 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 — KS C 5636-1989 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) TW — CNS 5205-1996 Republic of China (Taiwan) US 006 ANSI X3.4-1968 United States (ASCII) YU 141 JUS I.B1.002 (YUSCII) former Yugoslavia (Croatian, Slovene, Serbian, Bosnian)

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 SIS NATS, main set Sweden and Denmark (journalistic texts)

Code ISO- IR Approved by Origin Used in FI-SE 008-1 SIS NATS, main set Sweden and Finland (journalistic texts) 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	dec	hex	INV	T.61	US	JA	JA-O	KR	CN	TW	IRV	GB	DK	NO	NO-2	FI,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 characters, when preceded or followed with a backspace C0 control. This encoding method may be considered deprecated.

Later, when wider character sets gained more acceptance, ISO 8859, vendor-specific character sets and eventually Unicode became the preferred methods of coding most of these variants.

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.
• 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.

See also

• Basic Latin (disambiguation)
• ASCII
• Extended ASCII
• EBCDIC
• ISO/IEC 2022
• ISO 8859
• ISO 10646
• ISO/IEC 6937 (ANSI)
• C0 Controls and Basic Latin, in Unicode
• C Trigraph

References

1. ^ http://www.terena.org/activities/multiling/euroml/section04.html

External links

• Zeichensatz nach ISO 646 (ASCII) (in German)
• History at GNU Aspell website
• Character Tables by Koichi Yasuoka (see Domestic ISO646 Character Tables and Quasi-ISO646 Character Tables)
• Turkish Text Deasciifier a tool (based on statistical pentagram analysis of the Turkish language) which reverts an ASCII'fied Turkish text by determining the appropriate (but ambiguous) diacritics normally needed in Turkish but missing in the US-ASCII set.