A Tablebase is a file containing the perfect result information about all positions of a particular material setup, such as King and Rook versus King and Pawn.
Scid vs. PC can use Nalimov and Online Lichess and Shredder tablebases.
Nalimov bases are used by many chess engines. The filenames often end with the suffix .nbw.emd or .nbb.emd (for Nalimov Bases White/Black). All 3, 4 and 5 piece Nalimov tablebases can be used in Scid.
When a position found in a tablebase file is reached, the Game Information window (below the chessboard) will show the relevant information.
To load Nalimov tablebases, select their directory(s) via the Options--> Tablebase Directory menu item. Up to 4 directories may be selected.
You can configure the amount of information shown via the Options--> Game Information menus. Selecting Result and Best Moves gives the most information, but is often much slower than Result Only.
You can get more comprehensive information
from the
If Nalimov is selected, the Summary Frame (on the left) shows which tablebases Scid has found, and a summary for each tablebase. The Results Frame (on the right) shows optimal results for all moves from the current position displayed in the main window.
The top part of the summary frame lets you select a particular tablebase. Those available are shown in blue, those unavailable in gray, but you can select any tablebase. The lower part shows summary information for the selected tablebase. Not all tablebases have a summary recorded in Scid yet.
The summary includes the frequency (how many games per million reach a position with this material, computed from a database of more than 600,000 master-level games), a longest mate for either side, and the number of mutual (or "reciprocal") zugzwangs. A mutual zugwang is a position where white to move draws and black to move loses, or where white to move loses and black to move draws, or where whoever moves loses.
For some tablebases with mutual zugzwangs, the summary also includes a list of all of the zugwang positions or a selection of them. A full list for every tablebase is not feasible since some tablebases have thousands of mutual zugzwangs.
Results may be shown from local Nalimov bases (if installed) , or generated from an online lookup to Lichess or Shredder. The results frame is updated whenever the main chessboard changes.
The first line of local bases shows how many moves win (+), draw (=), lose (-), or have an unknown result (?). The rest of the frame gives a more detailed list of results, ranking them from shortest to longest mates, then draws, then longest to shortest losses. All distances are to checkmate.
In any tablebase position, it is often useful to know what the results would be if one piece was moved somewhere else. For example, you may want to determine how close a King has to be to a passed Pawn to win or draw. In endgame books this is often called the winning zone, or drawing zone, of a piece.
From the Results Board, this information is available by pressing the piece in question. This displays symbols representing what the result would be (with the side to move of the current position) if the selected piece was on that square.
There are five different symbols a square can have:
The Result Board cannot make use of online tablebases.
Olympuschess.com. (BitTorrent tracker, only 6 pieces)
http://tablebase.sesse.net (fastest mirror, EU)
Lichess Tables (mirror hosted by Lichess, EU)
Bob Hyatt's Ftp (Archive.org)
Online tablebase support requires Tcl packages http and tls, and are not available in the Game Info window.
Scid vs. PC can use the online tablebases from Lichess and Shredder.
The Shredder tablebase gives the true value of a position for up to 6 men, showing the depth to mate where relevant.
The Lichess Syzygy tablebase shows the depth to mate for up to 5 men and the DTZ for 6 to 7 men. DTZ means 'distance to zeroing' of the counter for the 50-move drawing rule. Syzygy tablebases do not aim for the fastest way to mate, but rather for the fastest way to make a winning capture or pawn move or give mate. This can be a bit unintuitive, but it allows perfect play, regarding outcome, even under the 50-move rule. If a win or loss occurs more than 50 moves after the 50-move-counter was last reset to zero, it is called a 'cursed win' or 'blessed loss', because under FIDE law 9.3 the result is a draw. Lichess will in a few cases give the depth to mate for 6 or 7 men, which is shown in braces next to the move.