A ROM is nothing more than a snapshot of the game's cartridge. Like you said, it's possible to get a ROM illegally off the internet, but you can get the ROM yourself straight from the cartridge with the proper hardware, which is legal.Same goes for BIOS, unless I'm mistaken. Of course it's not all as easy as it looks....Right. I don't think the GBA has a BIOS, though. I know nothing about the GBA's architecture, so I could be wrong. Yes, what I described would work for DS games, as well as games for pretty much every other gaming/arcade console out there. You'll need different ROM-reading hardware, but the basic process remains the same.