Endgame databases allow a chess program to play certain endgames perfectly (according to certain criteria such as minimum moves to mate) by storing the number of moves to mate or win (e.g. pawn promotion, capturing) for the superior side for every possible position. Endgame databases thus tend to be large. A 4-piece endgame such as KQKR or KBNK takes up 3 - 4 Mb of disk space, whereas 5-piece endgames such as the very difficult KBBKN may require as much as 100 MB of disk space! Sigma Chess supports 3 and 4 piece endgames, but currently not 5-piece endgames or higher.
When Sigma Chess is installed, a folder named Endgame Databases is created. In order to reduce the size (and hence the Internet download time) of Sigma Chess 6.2, this folder doesn't contain the actual endgame databases, but instead contains a number of small Endgame Database Generator applications for each of the supported endgames. Thus, for instance, if you want to use the KQKR database, you simply start up the "KQKR Generator" application.
Note 1 : The generation process is rather time consuming; it may take several minutes per database.
Note 2 : Sigma Chess expects all endgame databases to reside in the "Endgame Databases" folder. If the databases are moved, Sigma Chess cannot find them and will instead have to use the normal search engine.
Note 3 : The "Endgame Databases" folder only contains 4-piece endgame generators. However, the KQKR database also contains the KQK database. Additionally, the KRKN database also includes the KRK database.
Sigma Chess also supports the KPK database. But this is built in to the application because of its small size, and because it is the most frequently occurring of all the supported endings. Thus the KPK database is an internal database that is available at all stages of the search, so that, for instance, Sigma Chess doesn't trade off pieces in a won position only to end up in a drawn KPK ending. The other databases are external databases, that are only available at the initial root level of the search, i.e. in the current board position. To save memory, the KPK is not a full database in the sense that it stores the number of moves to mate/promotion for the winning side. Rather, each database entry simply indicates whether or not the corresponding position is a win for the player with the pawn. Thus, Sigma Chess will in some cases not find the shortest possible win, but it will find a fast win - if there is one!
Sigma Chess 6.2.1 User's Manual - Copyright (C) 2011, Ole K. Christensen