Intermittant lockup of VAX

[Doug Gwyn <gwyn>]

> We have experienced something like that when we installed a tri-density
> tape drive on one of our 750's.  Whenever the tape access was done
> and rewinding, the whole system froze until the spinning back had
> completed.  The bug was a hardware type in the tape controller.
> The manufacturer later sent us a revision and it is all okay now.
> Your problem may not be of tape drive but it is most likely
> hardware.

Older DEC magtape interfaces would generate two interrupts on rewind,
one when the controller had accepted the command and one when the
rewind was complete.  There have been many magtape device drivers that
don't handle this very well; I recall in the first release of VMS
one could take a TE-16 off-line manually while it was rewinding and
cause the whole operating system to freeze until the rewind completed.