From Just Solve the File Format Problem
KOI8 (or KOI-8; GOST 19768-74) is a family of 8-bit character encodings primarily for Cyrillic alphabets. Character codes 32-126 are identical with the corresponding ASCII characters. Cyrillic characters are ordered in phonetic correspondence to ASCII characters in the bottom half of the code table, not in native alphabetical order. This order is designed to maximize legibility if the 8th bit is stripped. The most widely used of these encodings is the Russian KOI8-R.