16 Jul
2015
16 Jul
'15
11:45 a.m.
----- Original Message -----
From: "Chuck Guzis" <cclist at sydex.com>
To: <General at classiccmp.org>;
"Discussion at classiccmp.org:On-Topic and Off-Topic
Posts" <cctalk at classiccmp.org>
Sent: Tuesday, July 14, 2015 5:47 PM
Subject: Re: Reproducing old machines with newer
technology
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
'C-Bus'.
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.
m