Emulators like PCSX2 do not include any BIOS files due to legal restrictions. To play PS2 games on a PC, you must provide a BIOS dump from a console you own. The SCPH-90001 BIOS is popular because:
It is the intellectual property of Sony Computer Entertainment. Distributing these files freely online is illegal in most jurisdictions. ps2 scph 90001 bios download free