Here is a short story about the final days of that hardware.
He ran a hex comparison against every known PS2 BIOS dump in existence—the SCPH-10000, the 30001, the 50001, the 70001. None of them contained anything resembling those strings. He checked earlier versions of the 90001 BIOS—v12, v14, v16. Nothing. Scph-90001-bios-v18-usa-230.rom0
– Region lock. This BIOS is intended for the USA/NTSC-U/C region. It expects NTSC video output, 60Hz refresh rate, and will only boot original discs with the correct region marking (SLUS-XXXXX for Sony-published titles, SCUS for first-party, etc.). Attempting to run a PAL (European) or NTSC-J (Japanese) disc with this BIOS would normally fail unless a modchip or emulator bypasses the check. The Deep Dive: Unpacking the SCPH-90001 BIOS (v18 USA 230