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From: rbl@nitrex.UUCP ( Dr. Robin Lake )
Newsgroups: comp.arch
Subject: Re: pdp-11/55
Message-ID: <555@nitrex.UUCP>
Date: Wed, 14-Oct-87 14:30:31 EDT
Article-I.D.: nitrex.555
Posted: Wed Oct 14 14:30:31 1987
Date-Received: Sat, 17-Oct-87 05:37:49 EDT
References: <1755@ncr-sd.SanDiego.NCR.COM> <275@usl>
Reply-To: rbl@nitrex.UUCP ( Dr. Robin Lake )
Organization: The Standard Oil Co., Cleveland
Lines: 31
Keywords: PDP 11/20, MMU

In article <154@aa.ecn.purdue.edu> stuartb@aa.ecn.purdue.edu.UUCP (Brian Stuart) writes:
>Please forgive me if I screw this up as it is my first net posting.
>
>However, I thought that I would add my 2 cents worth of misinformation
>regarding the history of PDP 11 systems.
>
>It is my understanding that a memory management unit was designed and
>built for the PDP 11/20.  However, exactly 3 of these units were constructed.
>They were as large (physically and numbers of cards, etc.) as the
>PDP 11/20 processor.  I don't know about the existance of the other
>two, but until recently, one of these units was resident in the
>Computer Science Laboratory at the Rose-Hulman Institue of Technology.

I believe one was constructed for a PDP-11 system at the Cleveland Clinic.
It was based on reed-switches.  The local DEC Field Service folks built
their own tester for it.  The Clinic has buried this project in oblivion,
for it was one of the better historical classic failures.  I used to use
it as a model of how things could go wrong in my classes.
I occassionally see one of the Field Service guys who worked on this system
and will ask him next time we meet.

The system was sold for scrap about 1975 --- and somewhere I have the card
of the remarketer that bought it.

The lack of a memory management unit on the PDP-11/20 was why I developed
the first solid-state disk, by the way.... but to conserve bandwidth,
that's only for those who request it!

-- 
Rob Lake
{decvax,ihnp4!cbosgd}!mandrill!nitrex!rbl