KOI character encodings

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KOI 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 Exchange".

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 look 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.


Modern KOI code pages are 8-bit extensions of ASCII. This family of encodings is also known as KOI8, KOI 8 and KOI-8.

The family members are:


There is also an obsolete 7-bit KOI7 code page, which does not contain lowercase letters. Codes of 31 Russian uppercase letters are just their KOI8 codes with the most significant bit cleared. Other code points are the same as in ASCII.

External links


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