A common stumbling block for newcomers is the concept of BIOS files. Many arcade manufacturers used standardized hardware across multiple games. For example, the Neo-Geo system used a standard BIOS that was identical for hundreds of different game cartridges.
In RetroArch, while running a game:
To understand MAME 2003 Plus ROMs, you must understand the underlying emulator's design: mame 2003 plus roms