How many disk controllers and/or ATA host adapters and/or SCSI host adapters can I put in my system?
From a hardware standpoint – as many as you want as long as there are no I/O port address, memory address or interrupt request signal conflicts. From a software standpoint it is a whole different story. First the simple x86 system hard disk controller configurations… • 1 ATA with 1 or 2 drives at I/O port addresses 1Fxh/3Fxh using interrupt request 14 (IRQ14). • 1 ATA with 1 drive at I/O port addresses 1Fxh/3Fxh using interrupt request 14 (IRQ14) plus a SCSI with 1 drive. • 1 SCSI with 1 or 2 drives. Other configurations are possible but are most likely not supported in the system or SCSI host adapter BIOS. And if its not supported at the BIOS level, it is unlikely to be supported by an operating system, especially DOS. The primary reason the above configurations are so restrictive is that the original IBM x86 BIOS supported only one MFM controller with a maximum of 2 drives. This restriction was then coded into much x86 software including many early version of DOS. The configuration
