On Fri, Feb 11, 2011 at 4:11 PM, Paul Anderson <useddec at gmail.com> wrote: AFAIK, the 1355 is a 150MB ESDI and the 1325 is a 69MB MFM drive. http://www.mfarris.com/hard_drives/micropolis/micropolis_1355.html http://www.mfarris.com/hard_drives/micropolis/micropolis_1325.html They seem to have the same physical geometry (1024 cyls, 5 platters, 8 heads), so perhaps you could move a set of boards from a 1325 a 1355 HDA, but I've never attempted such a thing. If you have a dead 1325, I would think that as long as the cables in/out of the sealed HDA matched, it would be safe to try - the heads and steppers probably aren't electrically different. In my collection, I have a small number of 1355s that came from the Sun3 era (and the SCSI-ESDI bridge cards to go with) and a larger number of 1335s that are either "real" DEC RD53s or from PCs that may eventually end up in a DEC box as an RD53 (the W7 jumper mod). I don't think I've ever seen a 1325 in the wild. I don't know why it is 2MB smaller than the 1335. -ethan P.S. - more raw data and jumper settings for the aforementioned drives http://www.4drives.com/DRIVESPECS/MICROPOLIS/2334.txt http://www.4drives.com/DRIVESPECS/MICROPOLIS/2339.txt http://www.4drives.com/DRIVESPECS/MICROPOLIS/2348.txt