Colossus Chess (1984)

Colossus Chess is a series of chess-playing computer programs developed by Martin Bryant, commercially available for various home computers in the 1980s.

Bryant started Colossus Chess in 1983, using his White Knight Mk 11 program, winner of the 1983 European Microcomputer Chess Championship, as a basis. It was developed on an Apple II, but was first commercially released for Commodore 64 as Colossus Chess 2.0 (CDS Micro Systems, 1984). A number of releases for 8-bit microcomputers followed. Version 3.0 was released in 1984 for the Atari 8-bit family of computers (published by English Software), followed by 4.0 in 1985 which was released on most formats of the day (published by CDS). Per other games of the time, the Acorn Electron implementation required that part of the screen memory be used as working space, causing the lower half of the screen to contain 'garbled' patterns.

Colossus Chess featured time-controlled play with game clocks, an opening book with 3,000 positions, and problem-solving mode that could solve normal mates, selfmates and helpmates. Pondering on opponent's time and a three-dimensional chessboard were introduced in Colossus Chess 4.0. All releases were written in the assembly language of the appropriate CPU; the ZX Spectrum version could examine an average of 170 positions per second.

Uncommon for microcomputer chess programs of the era, Colossus had a full implementation of the rules of chess, including underpromotion, the fifty-move rule, draw by repetition, and draw by insufficient material. Colossus was also able to execute all the basic checkmates, including the difficult bishop and knight checkmate.