[ih] Panel lights as a source of computer failure

[Leonard Kleinrock]

FYI, as you know, we have an original Honeywell-516 IMP at UCLA whose lights could be inspected if it helps in any of these questions. Of course as Steve said the 516 didn’t have that problem.
Len.


Sent from my iPhone

> On Sep 13, 2025, at 9:30 AM, Scott Bradner via Internet-history <internet-history at elists.isoc.org> wrote:
> 
> fwiw - I created the printer circuit layout that substituted LEDs for at least some of the IMPs
> for Bill Barker
> 
> and I was told that the "send a tech" went way way down from the once a week that it had been
> 
> Scott
> 
>> On Aug 21, 2025, at 3:39 PM, Alexander McKenzie via Internet-history <internet-history at elists.isoc.org> wrote:
>> 
>> Steve Crocker suggested that re-engineering the panel lights on the IMP
>> raised reliability from 98% to 99,98%.  That's not the only fix implemented
>> to up the reliability, but it was a significant part.  The whole story is
>> in the article "Seeking High IMP Reliability in the 1970' ARPAnet" by
>> Walden, McKenzie, and Barker, published in Vol 44, No 2 (April - June 2022)
>> of IEEE Annals of the History of Computing. The panel light problem was
>> specific to the second-generation Honeywell-316 IMPs; the original
>> Honeywell-516 IMPs did not have this problem.
>> 
>> Cheers,
>> Alex
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