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

Jim Scheef scheefj at netscape.net
Sun Aug 31 14:45:32 CDT 2008


ENIAC was a decimal machine, not binary. Mauchly wanted the Navy to be 
able to understand the proposal so they made it decimal. It was also not 
a stored program machine; it was rewired for each problem.

They were well into the design and construction when they realized that 
there was a better way to do this so their next machine, the UNIVAC I, 
was binary, stored program, and had about 30% as many tubes.

ENIAC, The Triumphs and Tragedies of the World's First Computer by Scott 
McCartney is my favorite on Eckert and Mauchly and their computers.


Brian L. Stuart wrote:
>> 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.

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