vacuum tube computer

From: Dave Dameron <ddameron_at_earthlink.net>
Date: Mon Feb 1 08:25:12 1999

At 09:19 PM 1/31/99 +0000, Tony wrote:

>> Am amazed you could build a computer like this with ~400 cards ~800 tubes.
>> That is similar to building a complete computer with 200 SSI TTL chips like
>> a 7400. Especially since a 24 bit latch could use 24 of the cards. I tried
>
>This doesn't sound out of line. The CPU of the PDP8/e on my desk is 3
>quad cards of TTL, mostly simple gates. Perhapes 250chips total. OK, some
>of them are more complex (like full adder circuits), but there's nothing
>that big in there.

Yes, I've never seen a schematic or prints of such a TTL computer, but
would love to.
I actually have some hardware now, the one from Don Tarbell, without
documentation.

Yes many systems were done with just transistors in a "small" system too. A
block diagram seems simple, it is all the control and glue logic that got
out of hand for my design. I didn't use a 74181 by the way, as couldn't see
the use of most of the functions besides A and B, A+B, !A, etc. Just
building an equivalent to a 74181 with only 7400 gates or valves would use
quite a lot (I haven't counted them).
>
>> a design once (on paper) with MSI ic's like 74193 counters, and it quickly
>> got out of hand, 100's of ic's.
>
>If you're going to allow anything in the TTL data book, then you can
>trivially make a CPU in 200 chips. You have to cheat slightly (74181
>ALUs, small PROMs, etc), but it can be done. It has been done - many times.

-Dave
Received on Mon Feb 01 1999 - 08:25:12 GMT