Terra will use Nalimovs compressed EGTB's up to 5 men positions
egtb's or End Game Table Bases are databases with absolutely correct information about who is winning and how many moves until mate or if it
s a draw. These tables are created by retrograde analyses, meaning in short that you start from all possible end positions and generates all moves backwards. After one step you have all mates in one(if we started from a mate position). Next step generates all positions leading to mate in one etc.
The main limiting factor is hard disk space when the number of pieces are increasing. Currently all 5 men positions are solved and some 6 men positions. All 6 men positions including pawns will require more than 1 Terrabyte (yes Terra!) of harddisk space. I haven't even tried to think about 7 men tables. When talking of 3, 4, 5 or 6 men positions we mean positions with that number of pieces including the kings. The class 2 men positions is of course not interesting. It is positions with only 2 kings on the board!
From my knowledge, the first who generated egtb's was Ken Thompsson (the creator of Belle). After him somewhat different schemes are tried first by Steven J. Edwards and then by Eugene Nalimov. Eugene managed to compress these bases quite substantially and it's the Nalimov egtb's that are state of the art right now.
Terra is using the Eugene Nalimov compressed table bases and I have included some of his code with his permission.
The files can be downloaded from Robert Hyatt's FTP site from the TB directory.
Sometimes you have to send the sequence 'egtb off' followed by 'egtb on' in order to make it happen.
Please give your comments in WinBoard Forum or email me. This document was updated 2004-08-02.