That's 'primary' encoding defined by GOST 19768-87 -- http://ru.wikipedia.org/wiki/%D0%9E%D1%81%D0%BD%D0%BE%D0%B2%D0%BD%D0%B0%D1%8F_%D0%BA%D0%BE%D0%B4%D0%B8%D1%80%D0%BE%D0%B2%D0%BA%D0%B0
It was sufficiently unpopular that most everyone used 'alternative' encoding (now known as CP866).