IBM 1620; was: Early Programming Books

Paul Koning paulkoning at
Mon Jun 21 13:53:19 CDT 2021

> On Jun 21, 2021, at 2:43 PM, Chuck Guzis via cctalk <cctalk at> wrote:
> On 6/21/21 10:55 AM, Paul Koning via cctalk wrote:
> memory. Nobody explained why that was a real problem.
>> Core memory is fairly sensitive to temperature.  In the case of the 1620, there is a heating system that brings the core memory box up to its operating temperature, which is why it takes several minutes after you turn on power before the machine will run.
>> Possibly the fan problem meant the temperature control system was no longer adequate.
> For some (jprobably hallucinatory) reason, I thought there was a project
> at CHM to replace the 1620 core stack with semiconductor memory.   Guess
> that never happened.
> --Chuck

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.


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