To understand the BIOS, one must first understand its host. The SCPH-90001 (the final digit typically denotes region, with '1' for North America) was the last hardware revision of the PS2, released in 2008. By this point, Sony had nearly a decade to refine the original 2000 design. The "90000" series is famous for two things: extreme compactness and the controversial removal of the original PS1 CPU (the IOP) that had served as the console's I/O processor. In its place, Sony integrated a "Deckard" PowerPC 405 core running an emulation software layer.
"Games crash during developer splash screens (like Sony Entertainment America)." Fix: This is not a BIOS error but a rounding mode issue. In PCSX2, go to Config > Emulation > EE/IOP and change "Rounding Mode" to "Nearest." The 90001 BIOS requires this for specific pre-2003 titles. Ps2 Bios Scph 90001 BETTER
"The BIOS setup menu looks corrupted (Japanese characters)." Fix: You may have accidentally used a mixed region BIOS. Download a verified NTSC-U/C 90001 dump. The corrupted characters indicate a Frankenstein BIOS (e.g., 90001 core with 70000 region metadata). To understand the BIOS, one must first understand its host