Schematics of Atanasoff-Berry Computer logic circuits?

Brent Hilpert hilpert at cs.ubc.ca
Fri Aug 29 13:55:10 CDT 2008


(Picking up where we left off.. a few messages sent to the list last week seem
to have been dropped during the outage.)

William Donzelli wrote:
> 
> >  Transisters were probably adapted much more
> >  quickly in switching networks than in signal processing for that
> >  reason and because no extra work had to be done to handle the stray
> >  capacitances that tubes suffer from.
> 
> Ultimately, yes, but in the 1950s, the machines were slow enough that
> the tiny capacitances in the structure of tube elements did not matter
> much.

I think, rather, that that's a good portion of the explanation of why they
were so slow.
Ballpark example, take a 12AU7: the sum of the grid-to-plate and
grid-to-cathode capacitance is around 3 pF. Suppose the network resistance
feeding the grid circuit is 250 KOhm, that's an RC time constant of 0.75uS,
a little better than just 1 MHz. (R can be reduced of course but power
consumption is then on the climb.)

(Not to say there weren't other reasons they were slow..)



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