[r0bbbo]

Something I've never been able to wrap my head around is how ROMs are dumped for emulators from cartridges? Dumping instructions and assets makes total sense to me, and packaging that up in a data file that can be interpreted by an emulator too, but how does an emulator model the hardware of every 'expansion' chip in a cartridge? How is that dumped from an original cartridge?

[RiverCrochet]

Expansion chips aren't ROMs; they need to be emulated as well.

The situation was IMHO a bit worse with the SNESs precedessor, the NES.

There were quite a few expansion chips--called mappers--even though their general function was expanding the NES's memory space instead of adding additional processors or capabiliies - and they were in most games because without them the NES is limited to 32KB of PRG ROM and I think 4KB or 8KB of CHR (graphic) ROM. Most games after the year the NES came out had them.

These all had to be reverse engineered along with the console itself - fortunately much simpler than reverse engineering an add-on CPU or accelerator though. Some are common and in many games (MMC1, MMC3) and others are pretty much for a specific game only (MMC2 is for Punch-Out only).

[cdchn]

They're not dumped. The emulator implementation recreates the expansion chip functionality in software. There are only so many expansion chips, so its not intractable.