PDP-11/45 RSTS/E boot problem

Paul Koning paulkoning at comcast.net
Wed Feb 13 14:03:41 CST 2019

> On Feb 13, 2019, at 1:20 PM, Jay Jaeger via cctalk <cctalk at classiccmp.org> wrote:
> ...
> Maybe that story about FE's using Unix as a test to confirm operation
> even when diagnostics said the machine was OK was not so much just a
> legend?

It still fels like a legend.  My experience with DEC field service engineers is that they used the diagnostics.  In the PDP-11 era, Unix knowledge around DEC was pretty sparse, especially early on when it could be found only in the Telephone Products Group (Armando Stettner).  RSTS would be more plausible, but I never saw that in the hads of FS engineers either.

By and large diagnostics would find problems.  I've seen a number in the 1970s, including a messy data path failure in the 11/45 MMU where we (college students) did the initial diagnosis while the FS engineer was on his way.

My suspicion is that things not solved by diagnostics would be escalated to the "wizard from Maynard".  And they'd probably start replacing whole subsystems.  I've seen that once, when our college RSTS-11 system (11/20, 16 DL-11 lines) was crashing on average once a day for months.  DEC brought in several of those "wizards".  The "fix" was to replace the 11/20 by a "spare part" -- an 11/45 with more memory, a DH11, and RSTS/E.

Decades later I was told that the wizards actually pinned the blame on the college FM broadcast transmitter, about 200 feet down the hall from the computer center.  That may well be, though I didn't heard that at the time.

RSTS did get used in manufacturing, at Final Assembly & Test sites like Westminster MA and Salem NH, where PDP-11 systems large enough to run RSTS/E were subjected to a load test of exerciser programs running under that OS.  The way it was explained to us is that a system that would be happy with such a test would also be happy with any customer application.  It's not clear if that was because RSTS would load things more than most, or was more finicky about hardware glitches than most, but it certainly was the practice for quite some time.  Of course, not all PDP-11 configurations could be tested that way.


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