SI9900 (was Re: new gifts)

From: Ethan Dicks <>
Date: Thu Apr 17 09:17:00 2003

--- Jeffrey Sharp <> wrote:
> On Wednesday, April 16, 2003, Ethan Dicks wrote:
> > My first 11/750 had an SI9900 on it from the day it was used by the
> > original owner. My 11/70s also have SI9900s... MASSBUS...
> The previous owner of my SI9900s said he had problems getting it to work
> between some CDC 9762s and a Unibus PDP-11. He said that it liked to
> perform a spiral write for him at inopportune moments.

Hmm... how nasty. I've never used the Unibus interface. I have what
I _think_ are a couple of Qbus interfaces (spares from an old SI FS
guy), but I've never even installed one to test.

> Has anyone, by chance, heard of anything like this before regarding the
> SI9900?

I have no such experience, but we had Fuji drives, not CDC drives, and
we weren't using a Unibus interface, so YMMV.
> And when it interfaces to Qbus/Unibus, what does it look like to the rest
> of the system? MSCP? Or maybe it was configurable?

I doubt it was MSCP unless that was done on the Unibus/Qbus card itself.

We used the VMS DRDRIVER on the 11/750 (and its equivalent under SysV
and 4BSD, IIRC). One perpetual problem we had was that our big drive
was a Fuji Eagle, which does not equate to any DEC drive capacity.
Our choices were to ignore massive amounts of storage, or patch the
driver. We were dependent on SI for upgrade after upgrade. It would
have been a real nightmare, except that our system drive was a Fuji
160MB disk (with the translucent lid) that appeared to be two real
RM03s to the VAX. No patches required. As far as the VAX thought,
there were a pair of 9762s out there on the end of the cable.

I think a Fuji Super Eagle matched up closely enough with something
real that you didn't have to patch the driver if you had one of those,
but we didn't, so I'm not certain of that.

This is a "problem" that MSCP relieves you of (that and manual bad
block replacement). The SI9900 would have been *the* way to go
for our 11/750 if it had been MSCP. As it was, we never bought any
disks beyond the original two spindles (both of which I now have in
storage). When we went to expand the machine, we kept its MASSBUS
boot drive and added a UDA50 + RA81s (they weren't cheap, but they
were physically smaller than the SI9900 + drives, and they were

If I ever get any SI9900-compatible SMD drives (not SMD-E, AFAIK) in
the 8" range, I might drag a controller home from the farm and stick
it on a MicroVAX to see how it behaves. I just don't want to be
humping around a bunch of Fuji Eagles. They look nice exactly where
they are. :-)

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Received on Thu Apr 17 2003 - 09:17:00 BST

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