A self-hosted system, by default, detects the disk controller that's installed on the system, and then starts the appropriate driver for it.
On a self-hosted system, the diskboot utility in the OS image starts the block I/O drivers. If you want to change the way that the driver is started, you'll need to change the startup image and the options to diskboot. For example:
diskboot -o devb-eide,blk cache=30m
For more information, see Controlling How Neutrino Starts, and diskboot in the Utilities Reference. The drivers for hard disks load the cam-disk.so shared object, which provides a common access method for hard disks.