I can't really give a great answer to that, pretty sure it was all just electrical hardware. I'm curious now, I'll look around and let you know if I find something.

Edit: yep, no code, just circuits. Here is the original circuit diagram from Atari

[–] f4f4f4f4f4f4f4f4@sopuli.xyz 12 points 1 day ago

Many 80s games have an amusing hybrid design. Galaga has its game code and sprites in ROM, but has an entire custom chip that is a dedicated circuit for generating the ship explosion sound, another custom chip that only makes the scrolling starfield, etc.

[–] who@feddit.org 7 points 1 day ago

This is also how some old glass terminals worked.