KOI character encodings

KOI (КОИ) is a family of several code pages for the Cyrillic script. The name stands for Kod obmena informatsiey (Russian: Код обмена информацией) which means "Code for Information Interchange".

A particular feature of the KOI code pages is that the text remains human-readable when the leftmost bit is stripped, should it inadvertently pass through equipment or software that can only deal with 7 bit wide characters. This is due to characters being placed in a special order (128 codepoints apart from the Latin letter they sound most similar to), which, however, does not correspond to the alphabetic order in any language that is written in Cyrillic and necessitates the use of lookup tables to perform sorting.

These encodings are derived from ASCII on the base of some correspondence between Latin and Cyrillic (nearly phonetical), which was already used in Russian dialect of Morse code and in MTK-2 telegraph code. The first 26 characters from А (0xE1) in KOI8-R are А, Б, Ц, Д, Е, Ф, Г, Х, И, Й, К, Л, М, Н, О, П, Я, Р, С, Т, У, Ж, В, Ь, Ы, З.

KOI-7
Main article: KOI-7

The original KOI encoding (1967) was a 7-bit code page named KOI-7 (КОИ-7), which did not contain lowercase letters. In KOI-7, the codes of the 31 or 32 Russian letters are ordered according to the Latin letters. Other code points are the same as in ASCII (however, the dollar sign $ (code point 24hex) may be replaced by the universal currency sign ¤).

KOI-8
Main article: KOI-8

KOI-8 (КОИ-8), standardized in 1974 by GOST 19768, is an 8-bit extensions of ASCII.[1][2] Originally it only included 32 lowercase and 31 uppercase Russian letters.

Later derivatives of KOI-8 constitute the family of encodings variously known as KOI8, KOI 8 and KOI-8.

The family members are:

Additionally, GOST R 34.303-92 defines "KOI-8 V1" which is ISO-IR-153, and "KOI-8 N1" and "KOI-8 N2" which are variants of Code page 866.[16] These do not follow the KOI-8 layout.

DKOI
Main article: DKOI
See also: EBCDIC 410, EBCDIC 880, and EBCDIC 1025

DKOI is an EBCDIC-based encoding used in ES EVM mainframes. It has been defined by several standards: GOST 19768-74 / ST SEV 358-76, ST SEV 358-88 / GOST 19768-93, CSN 36 9103.[17]

There are two variants:

  • DKOI K1 (ДКОИ К1), each Cyrillic letter is given its own code point.
  • DKOI K2 (ДКОИ К2), some Cyrillic letters (А, В, Е, К, М, Н, О, Р, С, Т, Х, а, е, о, р, с, у, х) are merged with visually identical Latin letters.

Latin variants

Some encodings are called KOI, but define Latin alphabets:

  • KOI8-CS[18] / KOI8-CS2[17] for Czech and Slovak (ČSN (Czech technical standard) 369103, devised by the Comecon. This encoded Latin with diacritics, as used in Czech and Slovak, rather than Cyrillic, but the basic idea was the same - text should remain legible with the 8-th bit cleared, thus e.g. Č became C etc.).
  • KOI8-L2 "Latin-2" (defined in CSN 36 9103), ISO IR 139[19] (almost identical to ISO 8859-2 (1987), but has the dollar sign and currency sign swapped)
  • DKOI CS2 (defined in CSN 36 9103)[17]
  • DKOI L2 (defined in CSN 36 9103)[17]

References
  1. Czyborra, Roman (1998-11-30) [1998-05-25]. "The Cyrillic Charset Soup". Archived from the original on 2016-12-03. Retrieved 2016-12-03.
  2. Flohr, Guido; Chernov, Andrey A. (2016) [2006]. "Locale::RecodeData::KOI_8 - Conversion routines for KOI-8". CPAN libintl-perl. 1.0. Archived from the original on 2017-01-15. Retrieved 2017-01-15.
  3. da Cruz, Frank (2010-04-02). "Kermit and MIME Character-Set Names". The Kermit Project. Columbia University, New York, USA. Archived from the original on 2016-12-03. Retrieved 2016-12-02.
  4. Demchenko, Yuri V. (1997-11-13). Registration of a Ukrainian Cyrillic Character Set KOI8-RU (as extension to Russian KOI8-R and ISO-IR-111) (Report). Internet Engineering Task Force.
  5. Flohr, Guido (2016) [2006]. "Locale::RecodeData::KOI8_RU - Conversion routines for KOI8-RU". CPAN libintl-perl. Archived from the original on 2017-01-15. Retrieved 2017-01-15.
  6. "SBCS code page information - CPGID: 01167 / Name: Belarusian/Ukrainian KOI8-RU". IBM Software: Globalization: Coded character sets and related resources: Code pages by CPGID: Code page identifiers. IBM. C-H 3-3220-050. Archived from the original on 2017-02-18. Retrieved 2017-02-18.
  7. "CCSID information document; CCSID 1167; KOI8-RU". IBM. Archived from the original on 2017-02-18. Retrieved 2017-02-18.
  8. Leisher, Mark (2008) [1999-12-20]. "KOI8-RU Belorusian/Ukrainian Cyrillic to Unicode 2.1 mapping table". Department of Mathematical Sciences, New Mexico State University. Archived from the original on 2017-02-19. Retrieved 2017-02-18.
  9. Flohr, Guido; Davis, Michael (2016) [2006]. "Locale::RecodeData::KOI8_T - Conversion routines for KOI8-T". CPAN libintl-perl. Archived from the original on 2017-01-15. Retrieved 2017-01-15.
  10. Discussion
  11. "IANA Character Sets".
  12. ECMA-113. 8-Bit Single-Byte Coded Graphic Character Sets - Latin/Cyrillic Alphabet (1st ed., June 1986)
  13. "Cyrillic encodings (Charsets). Small description".
  14. Leisher, Mark (2008) [1998-03-05]. "KOI8 Unified Cyrillic to Unicode 2.1 mapping table". Department of Mathematical Sciences, New Mexico State University. Archived from the original on 2017-02-19. Retrieved 2017-02-18.
  15. Winitzki, Serge (2002-01-29). KOI8-C (Report). Internet Engineering Task Force.
  16. (in Russian) ГОСТ Р 34.303-92. Наборы 8-битных кодированных символов. 8-битный код обмена и обработки информации. = 8-bit coded character sets. 8-bit code for information interchange.
  17. Petrlik, Lukas (1996-06-19). "The Czech and Slovak Character Encoding Mess Explained". cs-encodings-faq. 1.10. Archived from the original on 2016-06-21. Retrieved 2016-06-21.
  18. "Stanislav Pecha - ASCII". Archived from the original on 2011-03-21. Retrieved 2011-04-19.
  19. ISO-IR-139

Further reading
  • Kornai, Andras; Birnbaum, David J.; da Cruz, Frank; Davis, Bur; Fowler, George; Paine, Richard B.; Paperno, Slava; Simonsen, Keld J.; Thobe, Glenn E.; Vulis, Dimitri; van Wingen, Johan W. (1993-03-13). "CYRILLIC ENCODING FAQ Version 1.3". 1.3. Retrieved 2017-02-18.
  • "Kodierungen und Zeichensätze" [Encodings and character sets]. Robotron Technik (Virtual computer museum) (in German). 2016-11-29. ASCII-Code / KOI-Code. Retrieved 2017-02-21.
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