If you have storage space, keep all three regional 4MB BIOS files in the folder. AetherSX2 will let you select which one to use per game.
If your file is significantly smaller than 4MB (e.g., a few kilobytes), it is likely a corrupted dump or a shortcut file. A functional PS2 BIOS should be exactly . aethersx2 bios 4mb
That said, using the correct 4MB BIOS for your game region prevents a specific issue called where text displays as garbled symbols. If you have storage space, keep all three
Once imported, you will see it in a list. Tap the radio button next to it to select it. A functional PS2 BIOS should be exactly
Ensure your BIOS matches your game region (e.g., use a USA BIOS for NTSC-U games) for the best results, though AetherSX2 is generally region-free. 4. Pro-Tips for Performance