> it really just killed off having to buy an extra host bus adapter card to send the same command set.

Sometimes that stuff could get pretty baroque. Back in the day I had a 20 MB HD for my Atari 8 bit computer, which involved an adapter from the Atari proprietary bus to SCSI/SASI, then a second adapter from SCSI to the MFM HD interface. You needed one of the custom DOSes to make use of it, as the standard Atari DOS had never envisioned things like hard drives.