Corvus?

From: Frank McConnell <fmc_at_reanimators.org>
Date: Sun Feb 18 20:23:14 2001

"Iggy Drougge" <optimus_at_canit.se> wrote:
> While going through the manuals for a Stride 460 last night, I
> finally discovered what the LAN port was for - Omninet (Corvus). I
> know of exactly one other machine with Omninet- the Research
> Machines Nimbus. Was this network widespread once? What kind of
> topology did it employ? Are there NICs for any other computers,
> perhaps even PCs? Any information is welcome.

I'm not sure I would call it widespread, but it was significant enough
that the DEC marketeers working on the Pro 350/380 saw it as something
they would have to compete against with Ethernet. (Ref: presentation
about DEC's entries into the PC marketplace, at the Computer Museum
History Center sometime in 1997; sorry, don't have any other details
handy at present.)

In the mid-1980s and into the 1990s there were a number of competing
physical network media: Ethernet, ARCNET, IBM token-ring, Proteon
token-ring (Pronet), Starlan, Omninet and other things too. Some of
the other physical media had as a selling point that they were cheaper
to install than Ethernet: cheaper network interface adapters and
cheaper cabling.

Anyway, back to Corvus. Corvus got its start selling
parallel-TTL-interface hard disks for the Apple ][. A hard disk was
more expensive than an Apple, so they also sold a multiplexer option
that allowed the connection of up to eight computers' controllers to
one hard disk, and IIRC you could have two multiplexers between a
computer and its hard disk so you could actually have 64 computers on
one hard disk.

Corvus also made hard disk controllers for other hardware: I know
I've seen one for S-100, and have read of one for the PDP-11, and
that there were others. Same parallel interface.

Now, imagine a sort of star-topology network strung together with
34-pin ribbon cable. Imagine distance limitations, and imagine
stringing all that cable and trying to keep it from turning into a
tangle as computers get moved around. Not fun.

So the folks at Corvus came up with Omninet, a 1Mbit/s twisted-pair
serial bus (using RS-422 levels) that could support a couple hundred
addressable devices. You could either access your parallel hard disk
via a computer that was attached both to it and to the Omninet, or via
an Omninet Disk Server, which was really a dedicated computer with an
Omninet interface and a Corvus parallel hard disk interface.

Corvus made Omninet interfaces for a number of different computers.
Apple ][, IBM PC, DEC Rainbow, Apple Macintosh, and I don't remember
what else; those are the ones I've seen recently. They also designed
an Omninet interface into their microcomputer offering, the Corvus
Concept.

Omninet cabling was cheap: a single twisted pair bus. Connecting to
it was cheap: you could buy the official Omninet tap box and node
cable (two wires terminating in a mini phone jack) or you could just
splice your node cable (two wires) to the two wires of the two wires
of the bus pair. Omninet bus termination was a resistor across the
ends of the pair.

There was also a later Omninet II network that ran at 4Mb/s, but I think
that involved a two- or three-pair bus. The only interfaces I've ever
seen for Omninet II were IBM PC ISA cards.

NEC also had a preliminary data sheet for an IC (uPD72105) that did
Omninet in their 1987 Microcomputer Products data book, volume 2.

-Frank McConnell
Received on Sun Feb 18 2001 - 20:23:14 GMT