KOI8-B is the informal name for an 8-bit Roman / Cyrillic character set constituting the common subset of the major KOI-8 variants (KOI8-R, KOI8-U, KOI8-RU, KOI8-E, KOI8-F). Accordingly, it is closely related to KOI8-R, but defines only the letter subset in the upper half. As such it was implemented by some font vendors for PC Unixes like Xenix in the late 1980s.