OT: how big would it be? - test-drb@ccmp.vtda.org

20 Oct 1999

Hey!  That must be the same UART board I have lying about somewhere.  It has
a bunch of shift registers in to-5 cans (to save space) and calculates
parity using a JK flipflop.

This thread seems to have started with the notion of even building the
flipflops from discrete transistors and passives.  That 4x5-inch board would
grow to the size of a closet door using that thechnology.  What's more, the
power would have to be distributed with #16 wire.

Dick

-----Original Message-----
From: CLASSICCMP(a)trailing-edge.com &lt;CLASSICCMP(a)trailing-edge.com&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Wednesday, October 20, 1999 9:46 AM
Subject: Re: OT: how big would it be?

...
  I have trouble
with the notion of the uart filling a 9 x 11 board given
that I'm holding one that's occupying 4 x 5 inches in SSI. Yeah, the shift
registers would take a bunch of space but I don't see it using anywhere
near the amount of real estate suggested. 
I'd suggest a electromechanical (or optomechanical) UART instead.  You
know, like in a Teletype :-).

>> A pdp-8 (early) had a pannel roughly 24"x50" with flip chip modules
mostly
...
 >> transistors and the 4k core was a 10"
tall rack section. for rough
>> comparison.  In many respects the 8080 is a far more complex CPU and would
...
 >> be significantly bigger.  It would also be
slow compared to the NMOS part.
...

>I suspect you could build a pdp-8 using contemporary layout tools and discrete
...
 >technology that, excluding the core stack, was an
order of magnitude smaller.
...

And repackaging would also save a lot of money: a large part of the cost
of a Straight-8 is all those gold plated fingers and edge connectors, and
the backplane wiring.  Get rid of that - so that your CPU resides on
a single (even if large) PC board - and you're way ahead.  (Well, way
ahead if everyone else is still in 1965...)

>> Doing it in ttl or bit slices would still be big, I've done that.  using
>> 2900 parts(ca mid to late '70s) the CPU equivelent was over 100 chips
and
...
  > filled 4
10x8" cards. 
>That sounds about right; I recall building a PDP-11 clone using 2901/2910 parts
...
 >as part of an undergraduate CPU architecture course
in the same era and using
...
  about the same
number of parts. 
Of course it's also possible to do it on a single card using SSI and
MSI TTL, maybe with a few bipolar PROM's.  Take a look at the 11/04 CPU or
the original Nova, for example.

I recall - back in the mid-70's - that Radio Shack sold transistor-based
logic module kits (PC boards) that could be strung together to make
things like binary counters, etc.  Does anyone else here remember these?
Or, even better, still have the modules around?

--
 Tim Shoppa                        Email: shoppa(a)trailing-edge.com
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