As I understand it, the 9153 has a floppy drive, the 9154 doesn't, they are otherwise identical. I have a 9154, the controller board has a connector for the floppy drive, and a labelled DIP switch to say whether or not it's installed. I beleive, too, that one version of the 9153 used a double density drive turning at 600rpm, in fact the same unit as is used in the 9114B. Another version of the 9153 used a high density drive, probably turning at 300 rpm (so the data rate would be the same). Be warned that the floppy drive gets its power over some of the odd-numbered wires of the ribbon cable, there is no separate power cable That's the SubSet/80 command set. It's a subset of CS/80 (Command Set 80). These are the commands the unit responds to over the HPIB interface -- docvmentation for this does exist (the 'service manual' for the 9133 might well include it as an appendix [1]), but it's not easy to find. [1] I have a (paper) manaul called something like 'HP's 3.5" floppy drive service manual'. It's odd. It's got some alignment instructions for the original Sony drive (but the Sony manual is a lot more complete!), then details of the PSUs in the 9121/9133, etc. No full schematics, alas. But there's a useful appendix giving the command set. It would be hard to make a replacement drive to link to your existing controller (not least because docuemntation on this is somewhat minimal [2]), it should be possible to make, say, a module with an HPIB port on one side and SCSI on the other. It would respond to CS/80 or SS/80, and talk to a normal SCSI drive. I am suprised nothing like this exists commercially (or maybe it does, and I've not looked for it carefully enough). [2] I've not traced out scheamtics of the 9154 yet, it is on the to-do list. But they wouldn't be a lot of use -- from what I remember the controller board contains a 68B09, EPROM, RAM, HP's HPIB chip and a gate array that contains all the hard disk control stuff. The drive also has a couple of custom chips in it. So diagrams at that level won't help you make a replacement drive. It's possible to remove the PCBs from the drive without damaging it. After removing the drive and the mounting brackets from it, the bottom 'tray' unclips, it contains one PCB. You have to pull it hard enough to disconnect the plugs to the other PCB. Then hold the spindle motor rotor and remove the nut in the middle of that, and slide the rotor off the spindle. The other PCB is then easy to remove. -tony