IBM 1620; was: Early Programming Books

Rich Alderson cc at
Mon Jun 21 17:38:34 CDT 2021

> Date: Mon, 21 Jun 2021 16:02:20 -0400
> From: Paul Koning via cctalk <cctalk at>

>> On Jun 21, 2021, at 3:52 PM, Chuck Guzis <cclist at> wrote:

>> On 6/21/21 11:53 AM, Paul Koning wrote:

>>> Perhaps you were thinking about the CDC 6500 at the late lamented LCM?
>>> That got some replacement stacks, which was an interesting puzzle because
>>> the read data connection out of the memory modules is a differential analog
>>> signal carrying the sense wire data, so the replacement module had to
>>> produce signals of that form.

>> From whence did the LCM 6500 come?

> Some vague memory says Purdue.  LCM actually got it running, which was an
> interesting problem.  It required recreating the inter-chassis cables (since
> the original ones were cut as part of dismantling the machine) and restoring
> the cooling system.  That was a bit tricky since it uses non-PC coolant,
> which actually still exists but can't be manufactured any longer -- you have
> to use whatever recycled material still exists in the world, and find a
> graybeard AC tech who knows how to work with the stuff.

> I think the machine is pretty much original except that a few core stacks
> were busted so they were replaced by RAM based emulations.  And it may be
> that the original console display wasn't used because of worries of breaking
> it -- the design of that machine wasn't very good and it apparently has
> reliability issues.

As I was the original negotiator for the acquisition of the 6500 for LCM (not
yet LCM+L :-), allow me to chime in.

Paul Allen alerted me to the existence of a "surplus" CDC 6500 at the Chippewa
Falls Museum of Industry and Technology in early 2011.  (PGA was always on the
lookout for interesting systems, especially those with which he had a personal
connection.)  I spoke to several people at CFMIT, their BoD discussed the
possibility, and came back with a "No, thank you."

In early 2012, a management team was hired for the museum as we ramped up to
opening, consisting of an Engineering Manager and a Business Manager.  The
latter gentleman was an old friend of PGA and WHG, having been their boss when
they were PDP-10 programmers for the Bonneville Power RODS project; he also
negotiated the purchase of the Portland Trailblazers basketball team by PGA,
and a number of other deals along the way.  He picked up the 6500 acquisition,
convinced the BoD at CFMIT to sell PGA the system, and it came to pass.

We learned when it was delivered that the machine had been at Purdue for its 22
years of active service, from 1967 to 1989, and was purchased back by CDC to
donation to CFMIT, part of whose mission was to have at least one of every
machine designed by hometown boy Seymour Cray.  The CDC FEs used a Sawzall vel
sim. to remove all the interchassis cabling, since "no one will ever want to
run this thing again".

The Engineering Manager, who in previous life wrote the microcode for the XKL
Toad-1 System's XKL-1 CPU, hired a new Principal Engineer, Bruce Sherry, to run
the restoration of the 6500.  (Bruce designed the XNI-1 Ethernet board for the
Toad-1, then went off to Strobe Data to do designs like their Nova and PDP-11
clones.  He also designed the 2nd generation Massbus Disk Emulator at LCM.)
Bruce found that the company which originally built the cables still had the
Cray design files, so they could recreate them; the pins were silver rather
than gold or tin, so he had to buy a brick of silver bullion for the company
which made the pins (need: c. 10,000, minimum order: 50,000).

Bruce brought in a wonder worker from Strobe, the late David Cameron, to do the
wiring; between 2012 and 2020, when we closed down, we found *3* miswirings out
of that 10,000 or so.

Because of Cray's physical design for the memory, Bruce had to spec out a
plexiglass box into which he inserted a small memory card, in order to keep the
proper airflow characteristics in the memory bays.

Bruce's business card at LCM listed his title as "Technomancer".


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