MAME requires BIOS ROMs for certain arcade systems (Neo Geo, CPS-1, CPS-2, NES-based arcades). Without neogeo.zip in your ROMs folder, zero Neo Geo games will run.
Is downloading a full set of MAME ROMs theft? Yes. But is it also the only reason these games exist? Full Set Mame Roms Download
Many arcade games have no modern re-release. The Outfoxies (Namco, 1994) – never ported. Primal Rage (Atari, 1994) – last port was MS-DOS. Cadillacs and Dinosaurs (Capcom, 1993) – licensing hell prevents re-release. MAME requires BIOS ROMs for certain arcade systems
The Preservation Argument: Without MAME ROM sets, these games would be extinct. The original PCBs are failing due to capacitor rot. If the only way to play Sunset Riders in 2050 is a ROM from a full set downloaded in 2025, then the full set served as a digital ark. The Outfoxies (Namco, 1994) – never ported
The Ethical Compromise: If a game is available for purchase on Steam, GOG, or the Nintendo eShop (e.g., the Arcade Classics Anniversary Collection), buy it. Support the industry. Use ROMs only for the 5,000+ arcade games that are commercially dead.
If you want to earn achievements on arcade games, you need a "non-merged rollback set" – a specialized version that works with the RetroArch MAME core. These are smaller (30–50GB) and focus on playable games.