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.