BIOS files such as ROM1.bin and SCPH1000.bin need to be placed in the same folder where ROMs are stored for PS2emu to work. BIOSs are required for any PS2 emulator to work. BIOS stand for “basic input/output system,” and they are used in more than just PS2 emulators.
There are multiple BIOS files available for PS2 emulators. This includes SCPH1000.bin, SCPH100.bin and SCPH7003.bin. Players only need one of these files to make a PS2 emulator work. Each BIOS file is related to a different region in which the PS2 was released. For example, the SCPH1001.bin is the BIOS file for the PS2 that was released in America, while SCPH1000.bin and SCPH7003.bin are for the Japanese and European releases, respectively.