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the classical chess program for the PDP-8, written in the 70s by Digital Equipment Corporation instructor John E. Comeau in PAL-8, the PDP-8 assembly.


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CHEKMO-II is a chess playing program which will run on any PDP-8 family computer. The program will play either the white pieces or the black pieces, and will play and accept all classes of legal moves, including castling both short and long, en passant pawn captures, and pawn promoting moves to any legal promotion piece. The program prints out its moves in Algebraic Notation, and accepts moves using Algebraic Notation. Included in the command structure of the program are commands which allow you to input board positions using Forsyth Notation, and get a printout of the board at your terminal.

Known Deficiencies

CHEKMO-II has been programed to use the same strategy throughout the game. This strategy has been optimized for good play in the Middlegame, and Opening. As a result CHEKMO-II plays poor moves in some Endgame positions.

If either the white side or the black side becomes significantly more powerful than the other (about 4 queens) CHEKMO-II may play some strange, but legal moves. This is caused by overflow in an internal evaluator routine.

See also

Forum Posts

External Links


  1. ^ DECUS Program Library PDP-8 Catalog 1978 (pdf)
  2. ^ PDP-8 Chess (CHEKMO-II) Instructions
  3. ^ PDP-8 Chess (CHEKMO-II) Instructions
  4. ^ CHEKMO-II German manual (pdf)
  5. ^ Re: Old programs CHAOS and USC by Dann Corbit, CCC, July 11, 2015

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