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Tablebases

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. Tablebases for all positions up to five pieces (including the Kings) have been generated, and some simple six piece tablebases are also available.

Scid uses Nalimov tablebases, which are also 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.

Scid vs. PC can also lookup results from www.lokasoft.nl , but this information is not available in Game Information, only in the Tablebase Window, and can cause system lag.

Configuration

To load the 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.

The Tablebase Window

You can get more comprehensive information from the Tablebase Window (Control =). This shows the result with perfect play of all legal moves from the current position.

The window has two main parts. 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 Summary Frame

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.

The Results Frame

Results may be shown from local Nalimov bases (if installed) , or generated from an online lookup to lokasoft.nl. 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.

The Results Board

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.

Obtaining Tablebase Files

The tablebases are available from Bob Hyatt's Ftp and Chesslib.
Play With Arena distribute the 4 piece tablebases as a single file