All versions of a game (USA, Japan, hacks) are in one single zip file. This is the most space-efficient for storage but can be harder for some front-ends to read.
The Ultimate Guide to MAME ROM Packs: Everything You Need to Know all mame roms pack
These combine the parent and all clones into a single ZIP file. They save disk space and make management easier because every game is self-contained in one file. Non-Merged Sets: All versions of a game (USA, Japan, hacks)
The is a marvel of digital archaeology. It represents tens of thousands of hours of reverse-engineering, PCB dumping, and coding. Owning a full set is like holding a master key to every arcade that ever existed between 1975 and 2005. They save disk space and make management easier
: These combine the parent game, all its regional clones, and variants into a single ZIP. This is the most storage-efficient way to keep a complete set.