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When the Bendex G-21 system was removed from the fourth floor of Scaife Hall, it was replaced by a Digital Equipment Corporation PDP-11.

From:            "David Chou" <>
Subject:         RE: Athena
Date:            Fri, 26 Oct 2012 19:31:04 -0700


I don’t know if there is an interest for this in our CIT group, but Paul Allen has started a Living Computer Museum where he has resurrected a number of 20-30 year old computers into their native state, including OSes.  See

So far, the group has restored 3 DEC 10's/20, a VAX, many PDP-11s and an DG MV-8000.  Ironically these are all more familiar to me than the current generation of non-Windows computers.  And you can even get login accounts. We might need to resurrect some acoustic couplers and a VT100, however.


Dave's email reminded me that a VAX or a DEC-10 replaced the G21 on the fourth floor of Scaife.

At least I think it did. What do you guys remember about this?

Date:            Wed, 7 Nov 2012 12:11:10 -0500 (GMT-05:00)
From:            "J. Chris Hausler" <>
Subject:         Re: DEC-10

Hi Mark,

The southwest corner of the 4th floor of Scaife which originally housed the Computation Center's G-20's after their removal then hosted the Computer Science Department's PDP-10, a KA10, the first model of the PDP-10, built I believe with the same plug in cards called "flip chips" used on the PDP-8 and 8/S using discrete transistors.  I have this fuzzy memory that sometime in the 1970/71 year before the computing facilities were moved to the third floor of Wean in summer 1971, a second KA10 PDP-10 was acquired although minimally configured.  About this same time we got the first ever semiconductor memory I ever saw for a PDP-10 (possibly with it).  My memory of it was that it was made by RCA and the chips were 256x1 bit dynamic memories but again this is a very fuzzy memory.  I don't recall the total memory size.  Prior to this the Computer Science Department had already gone "off brand" and purchased a 16KW (IIRC) Ampex core and then later a 32KW (again IIRC) Ampex core unit to extend the original 10's memory.  The photo on your page I took in fall 1976 showing John Godfrey on top of a table in the Wean CS computer room shows two KA10's.  I'm assuming that these were the two original ones, but there was a lot of stuff in that room and I almost recall a third machine (but again real fuzzy memory).

73, Chris Hausler
From:            David Chou <>
Date:            Wed, 7 Nov 2012 08:48:36 -0800

It was two DEC PDP10s that fit into exactly the same space in the corner of the 4th floor.  I think it was KI10s followed by KI20s a few years later.

David Chou
Date:            Wed, 7 Nov 2012 12:54:25 -0500 (GMT-05:00)
From:            "J. Chris Hausler" <>

Hi Dave (and all),

It could not have been KI's.  The KI came along in the early 1970's after I was no longer working for the CS department and had left Pittsburgh.  KA, KI and KL consoles look quite different as well and the photo I took of John Godfrey on the Athena page in 1976 shows a pair of KA's.

As to acoustic couplers, back in the late 1970's I purchased a pair of Novation CAT's (see: ).  As of a few years ago one of them had failed but the other was still working fine (but I haven't had any cause to use them in a while :-). 

Just after that time frame, my employer at the time scrapped out a 10 year old late 60's Anderson Jacobson ADC-300 acoustic coupler housed in a nice wood box.  It was non-functional when I got it but the problem was a damaged microphone and I was able to get new an exact copy replacement and then it worked.  Not only pretty to look at (see: ) (and I also have a couple of black desk phones just like the one in the photo, courtesy Bell :-) but in addition to the RS-232 interface it had a 20 ma. current loop interface built in to directly support teletypes.  The unit worked fine at 10 cps but was a little shaky at 30 cps.  Unfortunately, due I think to failed electrolytic capacitors, it no longerfunctions, but it is still pretty to look at (after I removed a seriouslayer of dust...).

73, Chris Hausler
From:            "David Chou" <>
Date:            Wed, 7 Nov 2012 15:14:50 -0800

Well it's amazing what you can find on the Internet with Google.  CMU has owned KA's, KL's and 20's.  I do remember seeing multiple processors as I dropped in from time to time after I graduated.

Date:            Wed, 7 Nov 2012 21:52:25 -0500 (GMT-05:00)
From:            "J. Chris Hausler" <>

Hi Dave,

Neat Site!  I do recall seeing one of the KL's on a later visit but the only visits I recall before the the 1990's are that 1976 visit and another in the early 80's and I believe it may have been during that early 80's visit.  The KL I saw was not in the CS computer room pictured with John Godfrey during the 76 visit but in the area you would have once seen straight ahead beyond the hallway when you stepped off of the Wean elevators on the third floor.  That had originally been glassed in (I don't think it is anymore) and earlier had been the area where Gordon Bell and friends had constructed the C.mmp.  I saw the C.mmp during my 76 visit and so believe it must have been the early 80's visit when I saw the KL in that same area along the wall to the right but the memories are fuzzy at best.  That area as well as the former 360/1108 room which was to the left and the CS computer room which was to the right have been through a number of changes since...

Of course the joke about the KL was that the front panel was a PDP-11.  PDP-10 folks couldn't understand why anyone would use such an ugly wart as the face of their beautiful machine and PDP-11 folks couldn't understand why one would need all that useless junk behind their beautiful machine ;-)  I remember being at 1983 spring DECUS in St. Louis (still have the "official" coffee mug :-) right after DEC had announced the termination of the PDP-10 product line in favor of the VAX.  The mood was ugly... (PDP-10 folks had an even lower opinion of the VAX than of the PDP-11 :-)

73, Chris Hausler

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