INT 13h (the highest priority item in the BCV table), referred to as a BIOS Aware IPL Device (BAID) in the specification.

Multiple controllers can hook INT 13h at once. For instance, after the SCSI controller, an AHCI controller can also hook INT 13h by putting a call to the previous handler, which was stored in the IDT at entry 13h by the SCSI controller, at the end of its own handler, before it puts the address of its own handler into the IDT at entry 13h. The first controller to hook INT 13h will see that