What is this panic?

[irwin at uiucdcs.UUCP]

What is this panic? I had the opportunity to set down and have a talk
with the manager of our local branch of DEC.

To quote, "The 750s have a problem with translation buffer parity errors
when running 4.2BSD, if the Rev 7 has not been installed. (tbuf panics)
These errors go away if the machine is brought to Rev 7. In addition to
this, 4.2BSD also has problems with cache memory parity errors, which
also cause panic type crashes. These will be fixed with Rev 8, which will
be available in the spring of '85. There are fixes in our software, both
VMS and our version of UNIX, which gets around the bug, but not in 4.2."

I let him read the base note, to which this response is made, and pointed
out that the author stated that their machine was Rev 7 and was having
tbuf panics. He said that is the first case he knows of where those type
of crashes were a problem on a Rev 7 machine, running 4.2 and that there
well may be a hardware problem and may need a board replaced.

As to the memory time outs in the response before mine, it well may be
that the bug is a bad memory board. If there is a steady stream of errors,
the controller may be busy correcting errors, while at the same time getting
more errors, which hangs the controller so long that it does not respond
in time and a time out is declared. If 4.2 is being run on this machine,
it usually reports memory errors, and a look in /usr/adm/messages will
verify if there is a bad board. If there are, if the board can be removed,
it may be that the time out bug will go away.