Reproducing old machines with newer technology

Mike Stein mhs.stein at
Thu Jul 16 13:45:58 CDT 2015

----- Original Message ----- 
From: "Chuck Guzis" <cclist at>
To: <General at>; 
"Discussion at and Off-Topic 
Posts" <cctalk at>
Sent: Tuesday, July 14, 2015 5:47 PM
Subject: Re: Reproducing old machines with newer 

> On 07/14/2015 02:05 PM, Jay Jaeger wrote:
>> Going all the way back to at least the IBM 
>> 7090, and presumably the 709,
>> though I have not actually checked.  The B5000 
>> had IO processors as well.
> Again, you're missing the point.  The system 
> *starts* with a PPU and loads the CPU up to run. 
> OS was pretty much entirely within the PPUs. 
> PPUs have autonomous access to the entire memory 
> space of the CPU and use the "exchange jump" to 
> switch it to a task.
> --Chuck

----- Reply -----

Not the same thing of course but remotely 
on-topic, and I never miss an opportunity to put 
in a plug for Cromemco:

By comparison, Cromemco used semi-autonomous 4MHz 
Z80A SBCs for their I/O processors,  with 16KB of 
local RAM and up to 32KB of ROM; communication 
with peripheral cards is via a separate 50-pin 

What's interesting and sort-of-relevant is that 
later versions of Cromix (their UNIX work-alike) 
could use the IOP to run Z80 programs, especially 
useful in a system having only a 680x0 main CPU.

FWIW, their hard disk controller also used a 4MHz 
Z80A with 8KB ROM and 64KB RAM that could cache 4 
entire tracks.


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