vintage computers in active use

Jon Elson elson at
Fri May 27 11:20:57 CDT 2016

On 05/26/2016 10:40 PM, William Donzelli wrote:
>> Another CHM volunteer (from the PDP-1 Restoration Project) and I
>> pushed for an IBM 360/30 Restoration Project, and the ability to build
>> replacements for failed SLT modules was part of our plan.
> I am still trying to figure in which universe are SLT modules so rare
> that one needs to fabricate replacements.
OK, where can you buy some?  They haven't been made since 
about 1970.  IBM sent out a letter to all 360 users who had 
machines under contract, giving a date when they would no 
longer guarantee that any particular machine could be 
repaired, due to lack of spare modules, and a second (later) 
date when they would drop all contracts and no longer make 
ANY parts available, due to the need to keep the National 
Airspace System running.
The IBM 9020 system was composed of slightly modified 360/50 
and 360/65 processors, and attempts to replace them with 
more modern technology had several notable failures.  These 
systems were in use until ** 1989 **!
They were finally replaced with IBM 3083 processors.

I suppose somebody may have a warehouse full of old SLT 
cards, but I've certainly never heard of it.
SLT modules were NOT terribly reliable, as compared to MST 
or newer technologies.  Remember, SLT is DISCRETE 
transistors and diodes on ceramic hybrid substrates.  At 
least in my experience, mid-size 360's would need a card 
replaced every few months.  I have no idea what the failure 
rate would be in cold storage rather than in power-on 24/7, 
which is what they did at Wash U.  (ISTR that maybe Rolla 
shut their 360/50 down every night.  I don't know if that is 
worse due to thermal cycling or better due to less power-on 
But, I'll bet that oxygen and moisture will continue to take 
their toll at a slower rate.  Remember, all this gear is now 
about 50 years old!


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