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KOI8-R (RFC 1489) is an 8-bit character encoding derived from the KOI-8 encoding by the programmer Andrei Chernov in 1993 and designed to cover Russian, which uses the Russian subset of a Cyrillic script. KOI-8, in turn, is an 8-bit extension of the KOI-7 encoding, which inherited a phonetic correspondence of Russian and Latin letters from the MTK-2 teletype code. As a result, Russian Cyrillic letters in KOI8-R are in pseudo-Latin alphabetical order rather than the normal Cyrillic one like in ISO 8859-5. Although this may seem unnatural, this has the useful effect that if the 8th bit is stripped, the text remains partially readable in any ASCII-based encoding (including KOI8-R itself) as a case-reversed transliteration. For example, "Код для обмена и обработки информации" (the Russian meaning of the "KOI" acronym) becomes kOD DLQ OBMENA I OBRABOTKI INFORMACII.

KOI-8 stands for 8-bitnyy kod dlya obmena i obrabotki informatsii (Russian: 8-битный код для обмена и обработки информации) which means "8-Bit Code for Information Interchange".^[1] In Microsoft Windows, KOI8-R is assigned the code page number 20866. In IBM, KOI8-R is assigned code page 878.^[2][3] KOI8-R also happens to cover Bulgarian.

It lacks proper quotation marks for these languages: both «...» and the Bulgarian „...“. Windows-1251 does support these, as well as more letters, and has thus become more popular. KOI8-R is used by less than 0.004% of websites, mostly Russian and Bulgarian.^{[citation needed]} Unicode and UTF-8 is preferred to single-byte Cyrillic encodings in modern applications, Unicode contains 436 Cyrillic letters including for Old Cyrillic.

The following table shows the KOI8-R encoding. Each character is shown with its equivalent Unicode code point.

• KOI8-B, a derivation of KOI8-R with only the letter subset implemented
• KOI8-U, another derivative encoding which adds Ukrainian characters
• KOI character encodings
• RELCOM
• Windows-1251, another common Cyrillic character encoding

• Flohr, Guido; Kiss, Gabor; Chernov, Andrey A. (2016) [2006]. "Locale::RecodeData::KOI8_R - Conversion routines for KOI8-R". CPAN libintl-perl. 1.0. Archived from the original on 2017-01-15. Retrieved 2017-01-15.
• Kostis, Kosta. "koi8-r (Russian U*IX encoding, also used by RELCOM)". 1.20. Archived from the original on 2017-01-16. Retrieved 2017-01-16.
• RFC 1489
• "KOI8-R (RFC 1489)". Kermit. Columbia University. Retrieved 2020-06-24.
• 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 2020-06-24.

• Universal Cyrillic decoder, an online program that may help recovering Cyrillic texts with broken KOI8-R or other character encodings.
• "The Home of the KOI8-R since 1995". 1995. Retrieved 2016-12-05.
• Czyborra, Roman (1998-11-30) [1998-05-25]. "The Cyrillic Charset Soup". Archived from the original on 2016-12-03. Retrieved 2016-12-03.
• Hohlov, Yu. E. "Cyrillic Information Representation in Electronic Form - Character Set (Code Page) Tables". Archived from the original on 2016-12-05. Retrieved 2016-12-05.
• Nechayev, Valentin (2013) [2001]. "Review of 8-bit Cyrillic encodings universe". Archived from the original on 2016-12-05. Retrieved 2016-12-05.