The most common format. Clone games only contain the files that differ from the "Parent" ROM. You must have the Parent ROM in the same folder for the clones to work. How Much Storage Do You Need?
Want a practical next step? Search for “MAME 0.270 ROMs (non-merged)” on archive.org or your favorite private tracker — and grab ClrMAMEPro while you’re at it.
For 95% of users, a (a "best-of" set of 500-1,000 working games) is superior to a full set. It saves space, eliminates clutter, and skirts some legal gray areas (you can plausibly own 500 PCBs? No, but ethically, it's a smaller bite).
Once you have obtained the Roms, follow these steps to install and configure Mame:
: Advanced users using "front-ends" like LaunchBox that handle the dependencies automatically.