Nalimov tablebases

Nalimov tablebases are precomputed databases for endgame positions with three to six pieces, counting both kings. Eugene Nalimov developed them, and for many years they became a practical standard for engines and interfaces that needed exact answers in small endings.

Their main metric is DTM, or distance to mate. A probe does not estimate which side is better. It determines win, draw, or loss within the covered material and, when applicable, reports the distance to mate under play that shortens or delays it.

Nalimov introduced efficient indexing and compression methods that made tablebase probing practical during an engine search. Even so, the complete six-piece collection requires substantial storage, and its historic probing code has different integration conditions from newer alternatives.

Because DTM is not organized around the fifty-move counter, a position can be a forced mate mathematically yet a draw in a game where that rule can be claimed. Syzygy uses WDL and DTZ to address that issue differently. Gaviota also supplies DTM, but normally only through five pieces.