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Code page 866 (CCSID 866) (CP 866, "DOS Cyrillic Russian") is a code page used under DOS and OS/2 in Russia to write Cyrillic script. It is based on the "alternative code page" () developed in 1984 in IHNA AS USSR and published in 1986 by a research group at the Academy of Science of the USSR. The code page was widely used during the DOS era because it preserves all of the pseudographic symbols of code page 437 (unlike the "Main code page" or Code page 855) and maintains alphabetic order (although non-contiguously) of Cyrillic letters (unlike KOI8-R). Initially, this encoding was only available in the Russian version of MS-DOS 4.01 (1990) and since MS-DOS 6.22 in any language version.