When I set SATA to AHCI mode, my SATA DVD drive generates "ATAPI Incompatible" error during POST. However, the drive is functioning absolutely fine in OS environment and BIOS detects it correctly. This error is not displayed if SATA mode is set to IDE.
I assume this error is not really a problem at all and is quite logical - SATA DVD drives are not AHCI capable (I think). It can probably be ignored. Am I right?
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It most likely depends on what your motherboard is. Maybe someone else here with the same hardware can help you figure out what's happening, so please be more specific about what's on your computer.