The author of this article discovered that the Atari 2600 game Video Chess, which was released in 1979, operated on only 128 bytes of memory without using any RAM memory. The game was optimized to use only a 4K ROM cartridge. The AI code uses a full-depth analysis that includes quiescence search, and also has several other features that make it one of the most impressive Atari 2600 games ever produced. The article also discusses the challenges of reverse engineering the game and summarizes the disassembled and commented source code for Video Chess.
https://nanochess.org/video_chess.html