Originally Posted By rfka01

F9A0H transferring 1 or 0 here switches (F940 according to another page)
Probably not 0xf940 as that is almost certainly the scsi controller while the master pic is at 0xf840. The loop reading 0xf941 reads the fdc first then sends what looks like a scsi command to 0xf940. It also looks for 0xaa55 (the boot sector signature) in the buffer.