Didn't some
winchesters use the spindle motor as a generator to provide
the emergency retraction current?
The drives used in PC do that and have for many years but I never saw a
mainframe disk drive that did.
Yes, I was thinking of things like full-height 5.25" units. Larger
drives often had AC spindle motors which would clearly be unsuitable for
this trick (well, at least not simply...)
-tony