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

20 Oct 1999

Why not explore this problem from the standpoint of an FPGA?  When you
finish you'd still have the flexibility of a hand-built device, yet what you
learned in the process would potentially be of actual use?

Why squander your cash and intellectual resources on creating something the
folks in the '70's electronics industry were striving to avoid when you
could have the same mental exercise in a productive form that made the
design and implementation of your architecture the core of your effort
rather than issues which are no longer relevant, like power consumption,
packaging, and finding the appropriate materials from which to build your
device?  Signal routing is the one issue which persists from that era of
yesteryear when a CPU lived in multiple racks, but it's handled, at least
superficially, by the development software.  Sharing flipflop packages or
gates between two circuits on a backplane with 50 cards of logic in it is no
easy matter.  What's more, the propagation delays will slow your circuit
down to cycles in multiple microseconds, while correcting the associated
routing errors will take multiple days for each one.  While it's not
perfect, the FPGA approach allows you to have these experiences with a
"virtual" closet-sized backplane with similarly "virtual" cards
(modules) of
logic which you can design hierarchically and based on your needs, not on
what the local parts vendor happens to have.

Dick

-----Original Message-----
From: Mike Cheponis &lt;mac(a)Wireless.Com&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Wednesday, October 20, 1999 9:35 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...

-Mike Cheponis