IBM 1620; was: Early Programming Books

Paul Koning paulkoning at
Mon Jun 21 15:02:20 CDT 2021

> 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.
> No, it was definitely a CHM project--could have been for the 1401,
> though.    In way of comparison to the 6000 core, 1401 and 1620 memory
> is much larger, less dense and slower--and I don't believe that the
> machine architecture makes use of a read-modify-write that the 6000 so
> neatly exploited.
> From whence did the LCM 6500 come?
> --Chuck

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.


More information about the cctalk mailing list