For RetroArch, PSXONPSP660.BIN is the superior choice. It incorporates more internal hardware knowledge than any community reverse-engineered BIOS, and produces fewer edge-case crashes.
The 660 variant refers to —the final, most polished revision of this emulator. Later firmwares (6.61) didn't change the PS1 emulation, and earlier firmwares (like 3.03 or 5.00) had audio glitches or compatibility holes. Psxonpsp660.bin Retroarch BETTER
Open your PS1 core (e.g., PCSX ReARMed) and ensure it is set to look for the BIOS in the system directory. Troubleshooting For RetroArch, PSXONPSP660
Crucial Note: Some online sources list the exact size as 524,288 bytes. Be careful of fake or corrupted files—always verify the MD5 hash. Psxonpsp660.bin Retroarch BETTER