Console BIOS files were region-locked. A Japanese BIOS ( SCPH-1000 ) may not play North American games, or may display them in Japanese with incorrect video timings (NTSC-J vs NTSC-U). A "Full BIOS" setup requires a complete set of regional variants to ensure any ROM from any region boots correctly. Batocera attempts to auto-select the correct BIOS based on the ROM header region, provided the user has supplied all regional BIOS files.
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Verifying BIOS Integrity
Boot Batocera and press on your keyboard to open the file manager. Plug in a USB drive containing your unzipped BIOS files. Console BIOS files were region-locked