I had to double-check this because I was sure you must have made a typo. Indeed, it was 128
bytes:
https://en.wikipedia.org/wiki/Atari_2600In that time the code and "assets" (such as they were) didn't reside in RAM (it was all in the cartrige), so this was only for a game state. Still, other home computer systems at that time (while addmittedly a few times more expensive) had plenty more ram, measuring in kilobytes!