ENIAC tube count / was Re: Schematics of Atanasoff-Berry Computer logic circuits?

Brent Hilpert hilpert at cs.ubc.ca
Fri Aug 29 13:58:09 CDT 2008

"Brian L. Stuart" wrote:
> > (No doubt. I haven't seen a lot of the ENIAC electronic design but it certainly
> > was unusual with the stacked tubes and multiple B+ levels.
> I can't help but see Eckert as one of the truly brilliant
> engineers of the 20th century.

Something I've wondered about with ENIAC is just where did all those 18000
tubes go (as in, where were they used in the machine)?

With 20 accumulators of 10 decimal digits each, each digit being a decade ring
counter of flip-flops, that's:
   20*10*10*2 = 4000 triodes or 2000 duo-triodes.
Somewhere I got the impression that number was about doubled for support
circuitry around the ring counters, which would put the count around 8000 or
4000, depending on how one is counting.

The accumulators account for a substantial portion of the machine (the majority
of the rack panels). I know each panel had a fair bit of control-sequencing
circuitry, and the power supplies may have accounted for quite a number, but
still, where did all the other tubes go?

And how feasible would it have been to replace those ring counters with 4-bit
binary decade counters to save a lot of tubes? Perhaps it wouldn't have helped
much because of the way the values from each counter were transmitted around
the machine. Binary counters were around by then of course, I'm not sure when
binary counters were first wrapped into decade counters ( by late 40's at
latest). It would be fun to examine the ENIAC schematics for these sorts of

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