-----Original Message-----
From: Mike Cheponis <mac(a)Wireless.Com>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Date: Wednesday, October 20, 1999 11:28 AM
Subject: Re: OT: how big would it be?
> > Say someone were to home-build a CPU from
scratch using only individual
> > components, no ICs only modern discrete(?) components. How big would
the
> > CPU be? For comparison lets say it would be
an 8080 clone. Any
guesses?
It seems to me the Right Answer is to approximate the number of transistors
required. How many transistors did an 8080 have? (Do remember, however,
that the transistor count is actually less than you'd need with discrete
transistors, because the on-chip transistors can have multpile emitters or
gates or whatever in the same device.)
As for how "big" it would be (that is, its size), modern discrete
transistors
are available in tiny SOT-23 or even tinier packages.
Resistors are
available in 0402 and maybe smaller. Line widths on PC boards can perhaps
be as small as .002 inches, and they can be many layers, a dozen or more.
So, in order to compute the size, I think you'd need to make two estimates:
1) The number of transistors per cubic inch (or cm if you like those units)
2) The number of transistors required.
This assumes some packaging/connector allowance is taken into account to
estimate the number of transistors per cubic whatever.
------
IMHO, if you're going to build something from transistors, why not build
something that was originally built with transistors? For example, the
IBM 1620, 1130, 1401, etc. Or if you really want to get funky, try
something
like transistorizing a tube machine, like ENIAC or
JOHNNIAC or Bendix G-15.
-That- could be entertaining...
That might be an interesting thing to do but I have no information on any of
those cpus. Really, have to sit down and find "the ulimate" cpu to
transistorize. 4004 seems reasonable (from the new stuff), I would not want
to try and build a staight 8 from scratch. I work heavily now with xilinx
and embedded applications (pic and scienix).
Allison: You worked on transistor 8s? How did they impliment the 20mA
current loop. I posted a message a while back about how it *was* set up in
this cpu. The schematics of a PT08 show nothing other than one TTY line
right into the receiver board.
-Mike Cheponis