> It was the smallest implementation of chess on any computer until its record was broken in January 2015 by the PC-compatible BootChess.
with this:
> 1K ZX Chess uses only 672 bytes of RAM,[2] but implements chess rules except for castling, promotion, and en passant, including a computer opponent.
If you don't include castling, promotion, and en passant, the game isn't chess anymore, or at least it hasn't been for a couple hundred years.