OT: how big would it be?

From: daniel <daniel_at_internet.look.ca>
Date: Wed Oct 20 11:15:39 1999

-----Original Message-----
From: Mike Cheponis <mac_at_Wireless.Com>
To: Discussion re-collecting of classic computers
<classiccmp_at_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
>
Received on Wed Oct 20 1999 - 11:15:39 BST