The PSXONPSP660.bin BIOS is widely considered the superior choice for PlayStation 1 (PSX) emulation in RetroArch, particularly for performance-sensitive devices like the Miyoo Mini . Originally extracted from PSP Firmware 6.60, this "POPS" BIOS was optimized by Sony to run PS1 games on the PlayStation Portable's limited hardware. Why PSXONPSP660.bin is "Better"
The file must be named exactly psxonpsp660.bin (all lowercase). RetroArch cores are case-sensitive. Psxonpsp660.bin Retroarch BETTER
Simply adding the file isn't enough; you need to tell your PS1 core to prioritize it. Most users use Beetle PSX HW or SwanStation. For Beetle PSX HW: Go to Quick Menu > Core Options. Find System or BIOS. The PSXONPSP660
After placing PSXONPSP660.BIN in RetroArch’s system folder, load SwanStation and enable these settings: RetroArch cores are case-sensitive
On Linux or macOS, you can use the psx-bios-builder script (available on GitHub) that legally automates the extraction from a PSP firmware update EBOOT.PBP (which you can download directly from Sony's servers).
There are multiple PSP firmware versions floating around the internet (1.50, 3.71, 5.00, 6.60). Here is the hard truth: Version 6.60 is the mature, final, and most compatible firmware release from Sony.