Xref: utzoo comp.arch:10307 comp.misc:6361 comp.sys.att:6738
Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!tut.cis.ohio-state.edu!att!cbnewsd!jps
From: jps@cbnewsd.ATT.COM (j.p.schoonover)
Newsgroups: comp.arch,comp.misc,comp.sys.att
Subject: Re: AT&T 3B20D
Summary: Clarification
Message-ID: <240@cbnewsd.ATT.COM>
Date: 18 Jun 89 00:50:35 GMT
References: <226@cbnewsd.ATT.COM> <8906161850.AA19350@cunixd.cc.columbia.edu>
Organization: AT&T Bell Laboratories
Lines: 34

In article <8906161850.AA19350@cunixd.cc.columbia.edu>, gld@CUNIXD.CC.COLUMBIA.EDU (Gary L Dare) writes:
> In article <226@cbnewsd.ATT.COM> J. P. Schoonover wrote:
> >
> >I don't know that AT&T has tried to sell the 3B20D as a general purpose
> >mini, but I wouldn't recommend using it that way.  It's too old a machine.
> 
> I don't know if AT&T tried to *market* them as such, but they have been
> donating these machines to various universities including Columbia.  We
> received three, but they were decommissioned after two years because 
> their service contracts were *prohibitive* and the System V OS version
> was an old, beta - couldn't afford new code, hard to find a system
> manager full-time, no NFS so we could use them as communications hubs
> (I was very enthusiastic about them, as you can tell).  A shame.
> 
> I don't know how many of the recipients have their systems running and
> happy.  Is anyone out there part of the 3B20 user group, U3G??
> 
>  Gary L. Dare				> gld@eevlsi.ee.columbia.EDU

Gary, what you had were 3B20S machines, not 3B20D machines.  The 'S' stands
for Simplex and the 'D' stands for Duplex.  The Simplex was indeed sold
as a general purpose machine.  In fact, we still use them on the project
I work on and SVR3 is available (with RFS) for the Simplex, but the Duplex
is only used in switching systems as a fault tolerant processor.  The name
Duplex comes from the duplication of main memory and the CU.  You cannot run
both CU's at the same time.  The two CU's and memory are duplicated so
that when trouble is detected in one, the machine will automatically
switch to the other.  Also, there is no way to "upgrade" a simplex to a
duplex.


					J. P. Schoonover
					(312) 979-7907
					iwtds!jps