Multi-Micro-Channel bus systems, and thoughts on the Computer Society Digital Library.

Chris Zach cz at
Sun Jul 25 08:43:42 CDT 2021

Read that Personal Systems magazine from 1992 that was recently posted 
and enjoyed the article on the PS/2 295 system. I never heard about that 
one, the biggest PS/2's I worked on were the 95 systems with 486 
processors back at Covington.

One thing that popped out: The 295 was a multi-processor-ish system with 
two MCA busses. Granted they were decoupled with each processor having 
its own MCA bus but it got me to thinking: Were there other systems of 
that time that could use two MicroChannel busses?

I know of one: Back when I first started working at the IEEE Computer 
Society in 1993 they had a donated NCR 3550 system. Big box, mainframe 
sized with 4 486/50 CPUs in it and an MCA backplane. As I recall AT&T 
donated it to the CS but no one had a clue what to do with it.

It ran NCR Unix which wasn't interesting but when we started putting 
together the first E-Commerce systems in 1994 I decided to use it with 
Windows NT. Oddly enough it could run NT 3.51 (and later NT 4 with a 
HAL) and we put it online with Netscape Commerce server. Ran great and 
just like that we were doing E-Commerce for SuperComputing/95 
registrations. :-)

Later we started building the Digital E-Library on it. We needed a 
system that could do a lot of SGML-HTML conversions quickly as well as 
render TEK Math to .gif in real time. So we upgraded the 3550 with 8 
(later a total of 16) Pentium Pro CPUs and a second Microchannel bus.

We split the disks up with 2 4 port SCSI adapters on each bus along with 
a network port each and balanced RAID1 and RAID5 disks across the 
channels on both busses. Worked surprisingly well and allowed us to load 
all of the CS periodicals on the system along with a big Lotus Notes 
server implementation to run the commerce software and store the 
E-Accounts (still in use today!). The E-commerce system allowed people 
to renew their memberships with credit cards, and of course add 
subscriptions both in paper and on-line with instant access once the 
credit card was charged. For mid-1990's timeframes this was pretty 
advanced stuff.

Later when we composted PDFs we put those on there as well with the 
Article shopping cart so people could buy articles individually. Boy, 
people liked that a LOT. We did experiment with a digital credit system 
so people could buy points and use those to buy articles but I could 
never figure out how to make it tamper proof. Satoshi figured that one 
out a decade later, I wish I had thought of the checksum chain idea.... 
Oh well.

But the big point: Running two MCA busses on a SMP based multiprocessor 
system was quite possible and do-able at scale, however did any other 
company make a dual MCA bus system? I always found it impressive that 
Windows supported even that stretch of a configuration (seeing 16 
Pentium Pro CPUs running together as people hit the digital library en 
masse was *neat*) but I don't recall any other systems that did it.


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