29 Aug
2008
29 Aug
'08
12:01 p.m.
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