1K ZX Chess

Did You Know?

• The game implements chess rules except for castling, promotion, and en passant.
• David Horne published the full source code as a type-in program in a series of articles in Your Computer in 1982 and 1983.
• The program includes a computer opponent.

Reception

In 1982, Popular Computing Weekly described 1K ZX Chess as one of the most intriguing ZX tapes they had recently encountered. They praised its feature of showing the computer’s moves as it thought, and marveled at the achievement of writing a chess program in just 1K of machine code, asking readers if they could even imagine doing the same. The magazine recommended the cassette at its £3 price despite its limitations. The following year, Sinclair User noted the technical wizardry required to fit such a game into an unexpanded ZX81, highlighting its fast loading speed and quick move calculation given the memory constraints. Home Computing Weekly gave it three out of five stars, criticizing the confusing user interface but conceding that the game still required thought to beat. In a 1985 book on computer chess, Tim Harding called its creator a genius, though he described the quality of play as so poor that it would be hard to lose, and he faulted the backward algebraic notation. Still, he deemed the program a fantastic technical achievement. A later rebuild of the original source code detailed all the optimizations used. 1K ZX Chess placed second in a poll of ZX81 users for best software. Retrogaming Times Monthly called it the greatest programming feat in gaming history, and Kuro5hin agreed, labeling it the greatest program ever written. BootChess author Olivier Poudade praised the code, saying that initially writing a smaller chess program seemed impossible because Horne had already perfected it so thoroughly. Poudade admitted he could not improve on some of Horne’s methods and had to replicate them.