FPGA VAX update, now DIY TTL computers

[Allison]

>
>Subject: Re: FPGA VAX update, now DIY TTL computers
>   From: "Chuck Guzis" <cclist at sydex.com>
>   Date: Wed, 02 Nov 2005 22:41:42 -0800
>     To: cctalk at classiccmp.org
>
>On 11/3/2005 at 7:00 AM Jos Dreesen wrote:
>
>>Much too big to actually build in TTL.
>
>Consider the very old Packard Bell PB250--22 bit words, fewer than 400
>transistors and 2500 diodes, 63 instructions.  Power consumption about 40
>watts, exclusive of I/O:
>
>http://ed-thelen.org/comp-hist/BRL61-p.html  
>
>The trick, of course, is to use bit-serial methods.  It seems to me that
>one could greatly simplify construction of a homebrew machine that way.
>We're not doing this for speed, right?
>
>Cheers,
>Chuck

As they say in some parts "it depends".  ;)

I can think of three reasons to build a machine.  

Recreate a system that is scarce or unobtainium such as the Apollo Block 
One. Speed here is possibly important to understanding what it's limitiations
or capabilities were.

Experiment with an archetecture that may exist but is not a chip.  Some speed
would be nice here as you may end up running real code.

Or just to build a computer that one can completely understand why and how 
it works. Here speed is not essential, slow may aid is seeing all the bits 
work in real time.

It would be hard to beat commercial hardware.  However there is little 
reason for not pushing the logic some if you plan to run an OS on it.  
At the other extreme the ability to go glacially slow is a good debug 
tool (all them lights don't hurt either).



Allison