> Then the RAM state is compared after each frame, to verify that the C implementation is correct.

So not simply recreated, it's a 100% accurate replica of the original game. Crazy.

What, by the way, was the original SNES "OS" written in?

No OS. These games were hand written in assembly direct to the metal.

The source code of the SNES Doom port was open sourced if you wanna take a look: https://github.com/RandalLinden/DOOM-FX