Use psxpsp660.bin (optimized by Sony) or scph1001.bin (Standard US).
by checking its MD5 checksum. Which step are you stuck on? gingerbeardman/PSX - GitHub Download pSX BIOS bin
The internet, as it often does, whispered back with a thousand results. He was flooded with advice from forums like Reddit and GitHub. Scph1001.bin? (The classic North American BIOS) Scph5501.bin? (Better for newer models) Use psxpsp660
"Okay," he muttered, opening a search engine. "Download pSX BIOS bin." as it often does
PSXONPSP660.bin? (The legendary Sony-optimized 6.60 firmware version)