1K ZX Chess

1K ZX Chess is a 1982 chess program for the unexpanded Sinclair ZX81.

1K ZX Chess
1K ZX Chess - Sinclair - ZX81.jpg
Box cover
Designer(s)David Horne
Platform(s)Sinclair ZX81
Genre(s)Strategy board


1K ZX Chess's code takes up only 672 bytes in memory,[2] but implements chess rules except for castling, promotion, and en passant, including a computer opponent.[3] It was the smallest implementation of chess on any computer, although today that title is held by LeanChess with 288 bytes (less than half the size of 1K ZX Chess).[4] Developer David Horne discussed 1K ZX Chess and published the full source code as a type-in program in a series of articles in Your Computer in 1982 and 1983.[5][6][2]


Popular Computing Weekly in 1982 called 1K ZX Chess "one of the most interesting ZX tapes to pass through our office in recent weeks". It approved of the computer displaying moves while considering them and noted "the skills which went into writing a chess program in 1K of machine code. Is there anyone reading this who could even contemplate doing the same?" The magazine concluded, "Despite the limitations this is one cassette, at £3, which I would recommend."[7] Sinclair User in 1983 stated that "it takes some technical wizardry to squeeze this kind of game into the unexpanded ZX81". The magazine praised the game's quick loading speed, and found that it "makes its moves very fast for the amount of memory available for it".[3] Home Computing Weekly gave the game three out of five stars, criticizing the confusing user interface but stating that "it still produces play which needs some thought to beat".[8] Tim Harding wrote in a 1985 book on computer chess that "the man who did it must be some sort of genius". While describing 1K ZX Chess' quality of play as "so appalling that it would be hard to make it beat you" and criticizing the backward algebraic notation, he concluded that "the program is nevertheless a fantastic technical achievement".[9]

1K ZX Chess came in second place for best software in a poll of ZX81 users. Retrogaming Times Monthly described it as "history's greatest game programming feat";[10] Kuro5hin agreed, calling 1K ZX Chess "the greatest program ever written".[11] BootChess author Olivier Poudade praised 1K ZX Chess's code, stating that at first writing a smaller chess program "seemed impossible ... Horne had nailed it so much already". Poudade acknowledged replicating some of Horne's methods as he could not improve them.[1]

See alsoEdit


  1. ^ a b Stokel-Walker, Chris (2015-09-20). "The bitter rivalry behind the world's smallest chess program". The Kernel. The Daily Dot. Archived from the original on 2015-09-23. Retrieved 2021-03-07. In mid-1982, a small quarter-page advert appeared in a computer hobbyist magazine. For just £5 (about US$26.50 today), the ad’s pixelated block text promised a computer chess program with “absolutely flicker-free display” and an opponent who would make its move on average just six seconds after yours. “Sensational 1K ZX 81 Chess,” claimed the copy, and ignoring that today-inexplicable numerical assemblage, the important points are “sensational” and “chess.”
  2. ^ a b Horne, David (February 1983). "Full ZX-81 Chess in 1K". Your Computer. pp. 100–102. Retrieved 5 March 2018.
  3. ^ a b Gilbert, John (March 1983). "Sinclair acts to improve the standard of its named software". Sinclair User. pp. 62–63. Retrieved 28 January 2015. CS1 maint: discouraged parameter (link)
  4. ^ LeanChess - The world's smallest chess program
  5. ^ Horne, David (December 1982). "Chess in 1K". Your Computer. pp. 68–69. Retrieved 21 January 2015. CS1 maint: discouraged parameter (link)
  6. ^ Horne, David (January 1983). "1K Chess". Your Computer. pp. 81, 83. Retrieved 21 January 2015. CS1 maint: discouraged parameter (link)
  7. ^ Scot, Duncan (1982-07-15). "1K ZX Chess". Popular Computing Weekly. p. 12. Retrieved 1 February 2015. CS1 maint: discouraged parameter (link)
  8. ^ Elder, Ray (1983-03-08). "Which ZX81 programs are best?". Home Computing Weekly. pp. 21–22. Retrieved 1 February 2015. CS1 maint: discouraged parameter (link)
  9. ^ Harding, T. D. (1985). Price, Jill; Levy, David N. L. (eds.). The New Chess Computer Book. Pergamon Chess Series (2nd ed.). Pergamon Press. p. 161. ISBN 9781483140322. CS1 maint: discouraged parameter (link)
  10. ^ Sabbatini, Mark (January 2009). "The Thrill of Defeat: Catching the 1k Bug". Retrogames Times Monthly. Retrieved 21 January 2015. CS1 maint: discouraged parameter (link)
  11. ^ codemonkey_uk (2001-08-10). "The greatest program ever written". Kuro5hin. Retrieved 21 January 2015. CS1 maint: discouraged parameter (link)

External linksEdit