Oh yeah, speaking of setting up emulators, I figured I'd give OG Metal Slug a go on MAME or somesuch. Immediately felt like a caveman trying to bang rocks together. Fool is me for thinking I could drop the bios files in there and load the archive. What hubris.
...I'll have to do some proper reading on it later.
There's very annoying levels of dependencies between various roms when it comes to MAME because they split every part into the tiniest common factor among them. It's not just like throwing a PS2 bios to start up an emulator. What people call "bios packs" for mame are more like sound chip firmware, gpu firmware etc. And then if there's multiple versions of a firmware, the newer depends on the older and acts like a patch upon it, same for game ROMs, there's a main rom that has the common denominator among all versions, and if you download a version that's not the main rom it depends on it to pull the content it misses.
It's a little like playing with a very early day linux distribution before package management and dependency solving had been invented.
So.. the solution the community picked to sort out that problem is to make torrent packs that contain every. single. rom that has ever existed for mame.
Just google "pleasuredome mame".
Whenever new mame releases come out you just pick up the latest torrent and point it at your current folder to update.
If you're willing to use.. a few hundreds of gb of storage for this, it's the "I don't need to care about anything" nuclear solution to the mame problem. Everything becomes simple and trouble-free. If you have all the roms that have ever existed, MAME just works.