Edwards' Tablebases

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Edwards' Tablebases,
are three-, four and some five-piece tablebases constructed by Steven Edwards in the early 90s, initially for his chess program Spector. Edwards' Tablebases rely on Depth to Mate and the complete coverage for both sides, using one byte per position, with evaluations of the forms "mate in N", "lose (get mated) in N", "draw", and "illegal". Values for the number N (measured in fullmoves, not ply) for mates range from mate in 1 upto mate in 126 and for losses in 0 (lose in 0 means checkmated) to lose in 125 moves. Each file is for a given class (e.g., KBNK) and for a given side to move (e.g., White) [1]. After finishing the construction procedure in 1994, Steven Edwards made the whole data, documentation and a test program written in ANSI-C publicly available on the Internet. Until the advent of the compressed Nalimov Tablebases, Edwards' Tablebases were quite popular and used in several chess programs, such as Crafty, Gromit, and the commercial MChess Pro, to name a few.

Index Scheme

The index scheme for pawn-less endgames exploits the fourfold symmetry of the chessboard to restrict the last identified piece to the a1-d1-d4 triangle by horizontal, vertical, or diagonal reflections, and features vertical symmetry by confining one pawn to the queen-side flank for endgames with one pawn. Other schemes as applied for instance in Thompson's Databases, enumerating all legal positions of both kings as combined index and considering pawns can't reside on the first or eighth rank, feature denser index ranges than Edwards' [2].

See also


Forum Posts



  1. Steve Edward's Endgame Tablebase generator is now available for WIN95 by Mike Byrne, CCC, November 01, 1997
  2. Ernst A. Heinz (1999). Endgame Databases and Efficient Index Schemes for Chess. ICCA Journal, Vol. 22, No. 1, ps
  3. Courtesy Steven Edwards

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