8-bit Multiuser (was Multics)

Rick Bensene rickb at bensene.com
Thu Nov 15 10:17:56 CST 2007

 > Well the idea of muilt-processing on a 8 bit cpu (6809) 
> sounds nice. You know a floppy, hard drive, serial I/O (low 
> speed) all going at once could help a user use software effectively.
> Still waiting ... too bad GIMIX is not around anymore.
> Ben alias woodelf
> PS. I don't want a COCO 3 instead, I want a REAL computer.
> (Well I have PDP 8 for my real *classic* computer :).
Gimix built 6809 (and I believe, later, 68000)-based computers that ran
OS-9.  Their machines were very well-designed and built, and had a
reputation for being true "data center quality" rather than hobbyist
machines, though they did market to the "high end" of the hobbyist

OS-9 was a full multi-user operating system that ran on the 6809 (a
68K-based version which was dramatically enhanced over the 8-bit OS-9
was also marketed, which was quite powerful).

The 6809-based (8-bit) version of OS-9 could be run on the various
models of the Radio Shack Color Computer, but with floppy disc's I/O
bandwidth limitations, it was frustratingly slow on the Coco I.  The
later Coco II and Coco III made improvements in the I/O architecture,
and added some "memory management" capabilities to address some of these
problems, and with a hard disk connected, could serve up a small office
multi-user environment, although they were hardly what I'd call "data
center" grade equipment.

OS-9 was made by a company called Microware, and was really quite
amazing for its time.  Sometime in the 1980's (can't remember exactly
when, but I think it was after 1985) I built a homebrew 6809-based
computer that used OS-9, and could nicely service five users including
the console, all running simultaneously (terminals at 9600 baud), along
with background jobs that did things like printer spooling, a clone of
UUCP, and even a batch processing system. The system had a
DMA/Interrupt-based hard disk controller that I designed that interfaced
to a Micropolis 8" hard disk drive (can't remember the model number, but
I think it held something like 20MB, and used a pre-SCSI parallel
interface, that I got from the Tektronix company store for something
like $25), and an 8-port serial I/O card that had some local
intelligence (another 6809) that handled buffered input.

OS-9 had a very extensible and well-documented driver architecture that
made it possible to easily write device drivers for all of this custom
hardware.  It utilized bank-switched memory (It had 256K of memory in
four banks with a common area (I think it was the upper 1K of the 64KB
address space) that wasn't bank switched for I/O (the 6809 uses a
memory-mapped I/O methodology) and boot ROM.

It was a fun project (that was when I had time...don't know where it
went, but it's definitely not here now), and I learned a lot by
tinkering with it.  I still have most of the pieces of that system,
except the hard disk eventually died, which pretty much ended the
playing with it -- those old Micropolis 8" drives just aren't around
anymore, and there's no time to try to design a USB or SCSI interface
for it.

Those were the days...

Rick Bensene
The Old Calculator Museum

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