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

[Brian L. Stuart]

> 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)?
> ...
> 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?

It's been a while since I looked at it in any detail, but I
expect it's a lot like other design work.  The core functionality
takes 90% of the hardware and the interconnection takes the other
90%.  The bits like signal propagation and clocking and sequencing
logic and such always seem to take a lot more than we expect
them to, and I expect a lot of the tubes went there.  Plus you
had I/O as well, between the switch bank, the card devices,
the display panel, etc.

> 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
> questions.

I don't know that it was a matter of binary counters being wrapped
into decade counters as much as decade counters being a natural
design step from mechanical wheels.  The design and implementation
of them had been well-established in the radar world, and as I
understand it, Eckert was quite experienced in it.  I'm sure he
was also quite capable of designing a binary machine and of course
did so later.  But I expect that the fact that this was a first
of its kind machine and the fact that there was a military need
for it meant that confidence in the outcome was more important
than efficiency of material.  So using design elements that were
familiar and proven was a better engineering choice.

BLS