I thought it was clear enough..? The roms are renamed to their crcs For example, for the game 'invaders', usually you need invaders.e, invaders.f, invaders.g invaders.h If you opened my invaders.zip, you would see 0ccead96, 14e538b0, 6bfaca4a, 734f5ad8 This works because mame, kawaks, nebula, and final burn look at the crc first, not the filename. Only if a correct crc is not found, will mame look for matching filenames and issue a warning. Kawaks completely ignores filenames. Nebula and Final Burn haven't been tested, but I would expect them to work the same way as kawaks. Why do it? I have one zip file, the fully-merged set, containing the roms for the parent and all children within the one zip. This one zip is used by all 4 emus, and as we know the roms aren't always exactly the same between them. Further, I have multiple versions of some emus. It saves having lots of similar sets laying about. My kof2001 set has 45 roms in it - and it doesn't cover everything - still more roms to be found. I don't expect that you would like it or understand it, but it suits my purposes just fine.