By default: Documents\PCSX2\bios (Windows) or ~/Library/Application Support/PCSX2/bios (macOS/Linux).
The SCPH-90000 series was released in Japan in late 2007 and later in other regions as the SCPH-90001 (North America) and SCPH-90002 (Europe/Australia). This model is notable for several reasons: Ps2 Bios Japan Scph-90000 Download
The SCPH-90000 is one of the later model numbers for the PS2 in Japan. Released to denote revisions or changes in the hardware, each model number like SCPH-90000 signifies a specific set of technical specifications or region. Ps2 Bios Japan Scph-90000 Download