[TUHS] core

Clem Cole clemc at ccc.com
Tue Jun 19 22:58:36 AEST 2018

On Tue, Jun 19, 2018 at 8:23 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu>

>     > From: Doug McIlroy <doug at cs.dartmouth.edu>
>     > Yet late in his life Forrester told me that the Whirlwind-connected
>     > invention he was most proud of was marginal testing
> Given the above, I'm totally gobsmacked to hear that. Margin testing was
> important, yes, but not even remotely on the same quantum level as core.

​Wow -- I had exactly the same reaction.     To me, core was the second
most important invention (semiconductors switching being he first) for
making computing practical.   I was thinking that systems must have been
really bad (worse than I knew) from a reliability stand point if he put
marginal testing up there as more important than core.

Like you, I thought core memory was pretty darned important.  I never used
a system that had Williams tubes, although we had one in storage so I knew
what it looked like and knew how much more 'dense' core was compared to
it.   Which is pretty amazing still compare today.  For the modern user,
the IBM 360 a 1M core box (which we had 4) was made up of  4 19" relay
racks, each was about 54" high and 24" deep.    If you go to
CMU Computer Photos from Chris Hausler
​ and scroll down you can see some pictures of the old 360 (including a
copy of me in them circa 75/76 in front of it) to gage the size).

I broke in with MECL which Motorola invented / developed for IBM for System
360 and it (and TTL) were the first logic families I learned with which to
design.   I remember the margin pots on the front of the 360 that we used
when we were trying to find weak gates, which happened about ones every 10

The interesting part to me is that I'm suspect the PDP-10's and the Univac
1108 broke as often as the 360 did, but I have fewer memories of chasing
problems with them.   Probably because it was a less of an issue that was
causing so many people to be disrupted by the 'down' time.
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