OT: how big would it be?

From: daniel <daniel_at_internet.look.ca>
Date: Wed Oct 20 11:48:17 1999

-----Original Message-----
From: Richard Erlacher <edick_at_idcomm.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Wednesday, October 20, 1999 12:33 PM
Subject: Re: OT: how big would it be?


>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?
>

(if this was directed at me)

I have to design that kind of crap now, every day. I just got *into*
transistor computers and find it quite interesting to see what games I can
play with old RTL type stuff.

>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.
>

I design high speed logic (some basic config cpu cores) now using Xilinx and
even some AMD chips (yes, I use to use the MACH stuff) all with various RISC
chips. I don't want to come home at night and *continue* the same type of
design work (or code). I find it more entertaining to work on an 8/S , not
drop one in a chip [though that might be interesting]. I try to spend my
time on the old systems which is what taught me back in '79 so much about
the new ones.

This unit will be nothing more than a conversation piece (in my office,
hopefully doing some small task) and I hope to have some fun with quick and
dirty logic.

If my PDP-8/S wasn't so *mint* in the rack I'd rip it out, drop it in a 8/E
table top case and drag it into the office to do something fun.

john


>Dick
>
>-----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 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
>>
>
Received on Wed Oct 20 1999 - 11:48:17 BST