Just tried one last experiment, hooked up the SCSI interface from my W2K to the output on the 9100, removed the AM5380 (SCSI interface IC) from the interface board, then tried to read the 9100's on board SCSI drive - no luck, lastly unplugged the 9100 SCSI drive and plugged a Known-To-Be-Good SCSI drive to the internal SCSI buss and I CAN read and write to it with my W2K notebook. Thus the internal drive MUST be SCSI, but with an unknown low-level format. Now we just need a SCSI drive duplicator!
I misquoted. The drive isn't ESDI, its SASI. SASI was the predecessor to SCSI, only allowing 2 devices. The busses are similar, however. A SCSI device should work on a SASI bus. The disk format is one that Microware specified for their OS/9 operating system.