ISO/IEC 646 ''Information technology — ISO 7-bit coded character set for information interchange'', is an

ISO The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries. Me ...

/ IEC standard in the field of

character encoding Character encoding is the process of assigning numbers to graphical character (computing), characters, especially the written characters of human language, allowing them to be stored, transmitted, and transformed using computers. The numerical v ...

. It is equivalent to the ECMA standard ECMA-6 and developed in cooperation with

ASCII ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...

at least since 1964. The first version of ECMA-6 had been published in 1965, based on work the ECMA's Technical Committee TC1 had carried out since December 1960. The first edition of ISO/IEC 646 was published in 1973, and the most recent, third, edition in 1991. ISO/IEC 646 specifies a 7- bit character code from which several national standards are derived. It allocates a set of 82 unique graphic characters to 7-bit code points, known as the ''invariant'' (INV) or ''basic character set'', including letters of the

ISO basic Latin alphabet The ISO basic Latin alphabet is an international standard (beginning with ISO/IEC 646) for a Latin-script alphabet that consists of two sets (uppercase and lowercase) of 26 letters, codified in various national and international standards and u ...

, digits, and some common English

punctuation Punctuation marks are marks indicating how a piece of writing, written text should be read (silently or aloud) and, consequently, understood. The oldest known examples of punctuation marks were found in the Mesha Stele from the 9th century BC, c ...

. It leaves 12 code points to be allocated by conforming national standards for additional letters of Latin-based alphabets or other symbols. It also defines the ''International Reference Version'' (IRV), including a full allocation of 94 graphic characters, to be used when a specific national version is not required. As of the 1991 edition of ISO/IEC 646, the IRV and

are identical. Previous editions differed in only one or two code points.

History

ISO/IEC 646 and its predecessor

(ASA X3.4) largely endorsed existing practice regarding character encodings in the

telecommunications industry The telecommunications industry within the sector of information and communication technology comprises all telecommunication/ telephone companies and Internet service providers, and plays a crucial role in the evolution of mobile communications ...

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

only in that code point 0x24, ASCII's dollar sign was replaced by the international currency symbol . The final 1991 version of the code ISO/IEC 646:1991 is also known as ITU T.50, International Reference Alphabet or IRA, formerly International Alphabet No. 5 (IA5). This standard allows users to exercise the 12 variable characters (i.e., two alternative graphic characters and 10 national defined characters). Among these exercises, ISO 646:1991 IRV (International Reference Version) is explicitly defined and identical to

. The ISO/IEC 8859 series of standards governing 8-bit character encodings supersede the ISO/IEC 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/IEC 10646 standard, directly related to

Unicode Unicode or ''The Unicode Standard'' or TUS is a character encoding standard maintained by the Unicode Consortium designed to support the use of text in all of the world's writing systems that can be digitized. Version 16.0 defines 154,998 Char ...

, supersedes all of the ISO646 and ISO/IEC 8859 sets with one unified set of character encodings using a larger 21-bit value. ISO-646-JP-paths

A legacy of ISO/IEC 646 is visible on Windows, where in many East Asian locales the

backslash The backslash is a mark used mainly in computing and mathematics. It is the mirror image of the common slash (punctuation), slash . It is a relatively recent mark, first documented in the 1930s. It is sometimes called a hack, whack, Escape c ...

character used in filenames is rendered as ¥ or other characters such as

₩ The won sign , is a currency symbol. It represents the South Korean won, the North Korean won and, unofficially, the old Korean Empire won, Korean won. Appearance Its appearance is "W" (the first letter of "Won") with a horizontal strike ...

. Despite the fact that a different code for ¥ was available even on the original IBM PC's

code page 437 Code page 437 ( CCSID 437) is the character set of the original IBM PC (personal computer). It is also known as CP437, OEM-US, OEM 437, PC-8, or MS-DOS Latin US. The set includes all printable ASCII characters as well as some accented letters (di ...

, and a separate double-byte code for ¥ is available in

Shift JIS Shift JIS (also SJIS, MIME name Shift_JIS, known as PCK in Solaris contexts) is a character encoding for the Japanese language, originally developed by the Japanese company ASCII Corporation in conjunction with Microsoft and standardized as JIS ...

(although this often uses alternative mapping), so much text was created with the backslash code used for ¥ (due to Shift_JIS being officially based on ISO 646:JP, although Microsoft maps it as ASCII) that even modern Windows fonts have found it necessary to render the code that way. A similar situation exists with ₩ and

EUC-KR Extended Unix Code (EUC) is a multibyte character encoding system used primarily for Japanese language, Japanese, Korean language, Korean, and simplified Chinese characters, simplified Chinese (characters). The most commonly used EUC codes are va ...

. Another legacy is the existence of trigraphs in the C programming language.

Published standards

* ECMA-6 (1965-04-30), first edition (withdrawn) * ISO/R646-1967 (withdrawn), or ECMA-6 (1967-06), second edition (withdrawn) * ECMA-6 (1970-07), third edition (withdrawn) * ISO 646:1972 (withdrawn), or ECMA-6 (1973-08), fourth edition (withdrawn) * ISO 646:1983 (withdrawn), or ECMA-6 (1984-12, 1985-03), fifth edition (withdrawn) * ITU-T Recommendation T.50 IA5 (1988-11-25) (withdrawn), or ISO/IEC 646:1991 (in force), or ECMA-6 (1991-12, 1997-08), sixth edition (in force) * ITU-T Recommendation T.50 IRA (1992-09-18) (in force)

Code page layout

The following table shows the ISO/IEC 646:1991 International Reference Version character set. Each character is shown with its

equivalent. Code points open for substitution in national variants are shown with a grey background. Yellow background indicates a character that, in some variants, could be combined with a previous character as a

diacritic A diacritic (also diacritical mark, diacritical point, diacritical sign, or accent) is a glyph added to a letter or to a basic glyph. The term derives from the Ancient Greek (, "distinguishing"), from (, "to distinguish"). The word ''diacrit ...

using the

backspace Backspace (, ⌫) is the keyboard key that in typewriters originally pushed the carriage one position backwards, and in modern computer systems typically moves the display cursor one position backwards,The meaning of "backwards" depends on the dir ...

character, which may affect

glyph A glyph ( ) is any kind of purposeful mark. In typography, a glyph is "the specific shape, design, or representation of a character". It is a particular graphical representation, in a particular typeface, of an element of written language. A ...

choice. In addition to the invariant set restrictions, 0x23 is restricted to be either # or £ and 0x24 is restricted to be either $ or ¤. However, these restrictions are not followed by all national variants.

Composite Graphic Characters

According to ISO/IEC 646, every graphic character must be a spacing character; that is, it must advance the character position forward. As a result, non-spacing

combining character In digital typography, combining characters are Character (computing), characters that are intended to modify other characters. The most common combining characters in the Latin script are the combining diacritic, diacritical marks (including c ...

s are not permitted in any national version. This is in contrast to later standards such as ISO/IEC 2022 and

ISO/IEC 10646 ISO/IEC JTC 1, entitled "Information technology", is a joint technical committee (JTC) of the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). Its purpose is to develop, maintain and ...

which permit or include combining characters. Several spacing characters can be used as diacritical marks, when preceded or followed with a

C0 control to create accented letters, referred to as ''composite graphic characters'' in the standard. For example, the sequence may be used to image the character . This encoding method originated in the typewriter/ teletype era when use of backspace would

overstrike In typography, overstrike is a method of printing characters that are missing from the printer's character set. The character is created by placing one character on another one – for example, overstriking ⟨L⟩ with ⟨-⟩ results in prin ...

a glyph, and may be considered deprecated. This method is attested in the code charts for the IRV, as well as the GB, FR1, CA, and CA2 national versions, which note that , , , and may behave as the diaeresis,

acute accent The acute accent (), , is a diacritic used in many modern written languages with alphabets based on the Latin alphabet, Latin, Cyrillic script, Cyrillic, and Greek alphabet, Greek scripts. For the most commonly encountered uses of the accen ...

cedilla A cedilla ( ; from Spanish language, Spanish ', "small ''ceda''", i.e. small "z"), or cedille (from French , ), is a hook or tail () added under certain letters (as a diacritic, diacritical mark) to indicate that their pronunciation is modif ...

, and

circumflex The circumflex () is a diacritic in the Latin and Greek scripts that is also used in the written forms of many languages and in various romanization and transcription schemes. It received its English name from "bent around"a translation of ...

(rather than quotation marks, a

comma The comma is a punctuation mark that appears in several variants in different languages. Some typefaces render it as a small line, slightly curved or straight, but inclined from the vertical; others give it the appearance of a miniature fille ...

, and an upward arrowhead), respectively, when preceded or followed by a backspace. The current PL-2002 standard explicitly directs the use of the backspace and apostrophe to form Polish letters with an acute accent. Some editions of ISO/IEC 646 also suggest that the solidus may be used with the equal sign to compose the not equal sign, , and that the underscore may be used to effect underlined text. The tilde character was similarly introduced as a diacritic , although the standard is silent about its use. Later, when wider character sets gained more acceptance,

ISO/IEC 8859 ISO/IEC 8859 is a joint International Organization for Standardization, ISO and International Electrotechnical Commission, IEC series of standards for 8-bit character encodings. The series of standards consists of numbered parts, such as ISO/IEC ...

, vendor-specific character sets and eventually

became the preferred methods of coding accented letters.

Variant codes and descriptions

ISO/IEC 646 national variants

Some national variants of ISO/IEC 646 are as follows:

National derivatives

Some national character sets also exist which are based on ISO/IEC 646 but do not strictly follow its invariant set (see also § Derivatives for other alphabets):

Control characters

All the variants listed above are solely graphical character sets, and are to be used with a C0 control character set such as listed in the following table:

Associated supplementary character sets

The following table lists supplementary graphical character sets defined by the same standard as specific ISO/IEC 646 variants. These would be selected by using a mechanism such as shift out or the NATS super shift (single shift), or by setting the eighth bit in environments where one was available:

Variant comparison chart

The specifics of the changes for some of these variants are given in the following table. Character assignments unchanged across all listed variants (i.e. which remain the same as ASCII) are not shown. For ease of comparison, variants detailed include national variants of ISO/IEC 646, DEC's closely related National Replacement Character Set (NRCS) series used on VT200 terminals, the related European World System Teletext encoding series defined in ETS 300 706, and a few other closely related encodings based on ISO/IEC 646. Individual code charts are linked from the second column. The cells with non-white background emphasize the differences from

US-ASCII ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...

(also the Basic Latin subset of ISO/IEC 10646 and Unicode).

Related encoding families

National Replacement Character Set

The National Replacement Character Set (NRCS) is a family of 7-bit encodings introduced in 1983 by DEC with the VT200 series of computer terminals. It is closely related to ISO/IEC 646, being based on a similar invariant subset of ASCII, differing in retaining as invariant but not . All NRCS variants except Swiss retain in its ASCII position, and are therefore in conformance with ISO/IEC 646. Several NRCS variants are identical to ISO/IEC 646 variants, and others are very similar, with the exception of the Dutch variant.

World System Teletext

The European telecommunications standard ETS 300 706, "Enhanced Teletext specification", defines Latin, Greek, Cyrillic, Arabic, and Hebrew code sets with several national variants for both Latin and Cyrillic. Like NRCS and ISO/IEC 646, within the Latin variants, the family of encodings known as the G0 set are based on a similar invariant subset of ASCII, but do not retain either nor as invariant. Unlike NRCS, variants often differ considerably from corresponding national ISO/IEC 646 variants.

HP

HP has code page 1054, which adds the medium shade (▒, U+2592) at 0x7F. Code page 1052 replaces a few ASCII characters from code page 1054.

Derivatives for other alphabets

Some 7-bit character sets for non-Latin alphabets are derived from the ISO/IEC 646 standard: these do not themselves constitute ISO/IEC 646 due to not following its invariant code points (often replacing the letters of at least one case), due to supporting differing alphabets which the set of national code points provide insufficient encoding space for. Examples include: * 7-bit Turkmen (ISO-IR-230). * 7-bit Greek. ** In ELOT 927 (ISO-IR-088), the

Greek alphabet The Greek alphabet has been used to write the Greek language since the late 9th or early 8th century BC. It was derived from the earlier Phoenician alphabet, and is the earliest known alphabetic script to systematically write vowels as wel ...

is mapped in alphabetical order (except for the final-sigma) to positions 0x61–0x71 and 0x73–0x79, on top of the Latin lowercase letters. ** ISO-IR-018 maps the Greek alphabet over both letter cases using a different scheme (not in alphabetical order, but trying where possible to match Greek letters over Roman letters which correspond in some sense), and ISO-IR-019 maps the Greek uppercase alphabet over the Latin lowercase letters using the same scheme as ISO-IR-018. ** The lower half of the

Symbol A symbol is a mark, Sign (semiotics), sign, or word that indicates, signifies, or is understood as representing an idea, physical object, object, or wikt:relationship, relationship. Symbols allow people to go beyond what is known or seen by cr ...

font character encoding uses its own scheme for mapping Greek letters of both cases over the ASCII Roman letters, also trying to map Greek letters over Roman letters which correspond in some sense, but making different decisions in this regard (see chart below). It also replaces invariant code points 0x22 and 0x27 and five national code points with mathematical symbols. Although not intended for use in typesetting Greek prose, it is sometimes used for that purpose. ** ISO-IR-027 (detailed in the chart above rather than below) includes the Latin alphabet unchanged, but adds some Greek capital letters which cannot be represented with Latin-script homoglyphs; while it is explicitly based on ISO/IEC 646, some of these are mapped to code points which are invariant in ISO/IEC 646 (0x21, 0x3A, and 0x3F), and it is therefore not a true ISO/IEC 646 variant. ** The World System Teletext encoding for Greek uses yet another scheme of mapping Greek letters in alphabetical order over the ASCII letters of both cases, notably including several letters with diacritics. * 7-bit Cyrillic ** KOI-7 or Short KOI, used for Russian. The Cyrillic characters are mapped to positions 0x60–0x7E, on top of the Latin lowercase letters, matching homologous letters where possible (where в is mapped to w, not v). Superseded by the KOI-8 variants. ** SRPSCII and MAKSCII, Cyrillic variants of YUSCII (the Latin variant is YU/ISO-IR-141 in the chart above), used for Serbian and Macedonian respectively. Largely homologous to the Latin variant of YUSCII (following Serbian digraphia

rules Rule or ruling may refer to: Human activity * The exercise of political or personal control by someone with authority or power * Business rule, a rule pertaining to the structure or behavior internal to a business * School rule, a rule tha ...

), except for Љ (lj), Њ (nj), Џ (dž), and ѕ (dz), which correspond to digraphs in Latin-script orthography, and are mapped over letters which are not used in Serbian or Macedonian (q, w, x, y). ** The G0 sets for the World System Teletext encodings for Russian/Bulgarian and Ukrainian use G0 sets similar to KOI-7 with some modifications. The corresponding G0 set for Serbian Cyrillic uses a scheme based on the Teletext encoding for Latin-script

Serbo-Croatian Serbo-Croatian ( / ), also known as Bosnian-Croatian-Montenegrin-Serbian (BCMS), is a South Slavic language and the primary language of Serbia, Croatia, Bosnia and Herzegovina, and Montenegro. It is a pluricentric language with four mutually i ...

and Slovene, as opposed to the significantly different YUSCII. * 7-bit Hebrew, SI 960. The

Hebrew alphabet The Hebrew alphabet (, ), known variously by scholars as the Ktav Ashuri, Jewish script, square script and block script, is a unicase, unicameral abjad script used in the writing of the Hebrew language and other Jewish languages, most notably ...

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/IEC 8859-8. The World System Teletext encoding for Hebrew uses the same letter mappings, but uses BS_Viewdata as its base encoding (whereas SI 960 uses US-ASCII) and includes a shekel sign at 0x7B. * 7-bit Arabic, ASMO 449 (ISO-IR-089). The

Arabic alphabet The Arabic alphabet, or the Arabic abjad, is the Arabic script as specifically codified for writing the Arabic language. It is a unicase, unicameral script written from right-to-left in a cursive style, and includes 28 letters, of which most ...

is mapped to positions 0x41–0x5A and 0x60–0x6A, on top of both uppercase and lowercase Latin letters. A comparison of some of these encodings is below. Only one case is shown, except in instances where the cases are mapped to different letters. In such instances, the mapping with the smallest code is shown first. Possible transcriptions are given for some letters; where this is omitted, the letter can be considered to correspond to the Roman one which it is mapped over.

Footnotes

References

External links

ISO/IEC 646:1991 Information technology — ISO 7-bit coded character set for information interchange

(in German)

at

GNU Aspell GNU Aspell, usually called just Aspell, is a free software spell checker designed to replace Ispell. It is the standard spell checker for the GNU operating system. It also compiler, compiles for other Unix-like operating systems and Microsoft Win ...

website
ISO646 Character Tables Character Tables by Koichi Yasuoka (安岡孝)
(see ''Domestic ISO646 Character Tables'' and ''Quasi-ISO646 Character Tables'')

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. {{DEFAULTSORT:ISO IEC 646 Character sets Ecma standards #00646