If you download a Neo Geo game, it won't run without the specific BIOS file, usually named neogeo.zip . However, it gets more interesting. The Neo Geo was released in different regions (Japan, USA, Europe, Asia), and it had different modes (Arcade "MVS" mode and Home Console "AES" mode).
cpzn2.zip : Required for Capcom ZN1 and ZN2 hardware. namcoc74.zip : Often needed for various Namco arcade systems. qsound.zip : Not strictly a BIOS, but a "device set" required for audio in many Capcom games. Reddit +2 Setup Guide by Platform Platform BIOS Location Note Windows (Stand-alone) C:\MAME\roms\ Place the zip file here; do not unzip. RetroArch RetroArch/system/ or same as ROMs Location varies by core; often works best when in the same folder as the game ROM. Batocera / EmuDeck /userdata/bios/ or bios for mame
You have the game ROM, so why isn't it working? If you download a Neo Geo game, it
This contains the actual graphics, sound, and level data for a specific title. Reddit +2 Setup Guide by Platform Platform BIOS