) require Compressed Hunks of Data (CHD) files. For MAME 2003, you must use DAT Files: file with software like ClrMamePro to verify your romset matches the reference standard.
For a technical breakdown of why 2003 is still used despite being 'tragic' in accuracy compared to modern MAME, see the threads on ArcadeControls Rebuilding and Cleaning Sets Pleasuredome Reference Set Guide
Newer versions of MAME prioritize extreme accuracy, which requires significant CPU power. MAME 2003 strikes a balance, allowing it to run thousands of games at full speed on devices like the Raspberry Pi 3 or older mobile phones.
files for specific sound effects not included in the ROM zip. Games that used hard drives or CDs (like Killer Instinct
You may also see references to MAME 2003-Plus . This is an enhanced version of the original core that adds support for hundreds of additional games and features like CD-quality soundtracks.
Reference sets are usually distributed in one of three organizational structures, which dictate how files are stored and whether they need "parent" files to run:
For the data-driven archivists, here is the technical breakdown of the MAME 2003 reference romset.
Even with the reference set, users run into issues. Here are the top 3 errors on RetroPie/EmulationStation.