In a split set, the parent game contains all the major data. Clone games (like a Japanese release or a 2-player version of a 4-player game) only contain the specific files that differ from the parent. Saves an immense amount of hard drive space.
This is the standard format used by most RetroPie and MAME 2003 distributions. It optimizes space while keeping files neatly categorized. mame 072 roms
Understanding MAME ROM Sets: Split vs. Merged vs. Non-Merged In a split set, the parent game contains all the major data
Which are you using (e.g., RetroPie, Batocera, Android)? In a split set
When dealing with older MAME versions like 0.72, you will likely encounter three primary formats of ROM sets. Knowing how they work will save you hours of troubleshooting: