: If you are using the Beetle PSX or Beetle Saturn cores in RetroArch (which are based on Mednafen), these BIOS files must be placed in the RetroArch system folder instead of a firmware folder.
Mednafen does not emulate this firmware via high-level emulation (HLE). Instead, it requires a of the original BIOS. Why? mednafen bios
The Role and Importance of BIOS Files in the Mednafen Emulation Architecture : If you are using the Beetle PSX
The PlayStation core is one of Mednafen's most used features. It requires three regional BIOS files placed in the firmware folder. Required Filename Recommended Version scph5501.bin Japan scph5500.bin Europe scph5502.bin Sega Saturn (ss) mednafen bios