RD51
From Computer History Wiki
The DEC RD51 is a re-branded Seagate 5.25" Full Height ST-412 10MB MFM disk.
It is supported by the following DEC QBUS MFM disk controllers::
4.3 BSD disktab
rd51|RD51|DEC RD51 Winchester:\ :ty=winchester:ns#18:nt#4:nc#300:\ :pa#15884:ba#4096:fa#512:\ :pb#5716:bb#4096:fb#512:\ :pc#21600:bc#4096:fc#512: