: Every game ZIP file is completely standalone and contains all necessary files (including BIOS and parent files). This is ideal for RetroArch's playlist scanner but takes up slightly more space.
A is the canonical collection. If a ROM is in the MAME 0.78 reference set, it means the MAME developers tested that exact file, dumped that exact chip, and verified it against the original arcade PCB (Printed Circuit Board). mame 2003 reference romset