The PS2 BIOS is the firmware that initializes and controls the PlayStation 2 console. PCSX2, the PS2 emulator, requires a PS2 BIOS file to emulate the hardware accurately. Without the BIOS, the emulator cannot function correctly or boot games.
You can extract the BIOS from your PS2 using a memory card and a USB drive with software like BIOS Dumper. You’ll need a modded PS2 or access to homebrew software to perform this operation.