new disks, old DEC (was Re: 4.3BSD Quasijarus)

Ethan Dicks ethan.dicks at
Sat Dec 27 11:52:02 CST 2008

On Sat, Dec 27, 2008 at 11:39 AM, Dave McGuire <mcguire at> wrote:
> On Dec 26, 2008, at 11:04 PM, Bob Armstrong wrote:
>>  I've also got a 11/725 that's in good shape except for a few missing
>> pieces of sheet metal, but like Ethan I've no working RC25 drive.

I don't know about the state of your drive, Bob, but mine is merely
missing a cartridge so I can't spin up the fixed platter.  For those
that might not know, the RC25 is 25MB/25MB removable on one spindle.
I think the original idea was that you would put VMS on the internal
platter and swap out the cartridge for either backup/restore, and
perhaps installs, but in practice, VMS got large enough fast enough
that you really needed all 50MB for the OS and a few user dirs.

You _can_ fit 5.0 on it, I've seen it, but 4.x is a better fit.

>>  A UNIBUS SMD controller is an option - there are some small 8" SMD disks that mist
>> just fit inside the chassis in place of the RC25 - but a UNIBUS SCSI
>> controller would be a better way to go, since it'd be no problem to fit a
>> SCSI disk in there.  Unfortunately neither SMD nor SCSI UNIBUS controllers
>> are easy to come by.
>  5.25" SMD drives do exist; Seagate (and possibly others) made them.  I had
> a few at one point (1990?) but no more.  I know someone who has some but I
> doubt he'd turn loose of them.

I know I've seen SMD-E drives in 5.25" form-factor, but I don't know
if SMD-E drives are happy on an older SMD controller (despite using
SMD drives since 1984, I really don't know lots about their
limitations - I only ever worked with a couple of combinations that
were known to work - I never had to match up settings and cables,
etc., on random configurations as I later did plenty of times with MFM
and ESDI).

Given the drives I do have on hand, I would, of course, love to have a
Unibus SCSI controller (or 3-4 or them, really), but they were really,
really rare back in the day.  Every once in a while, I entertain the
idea of turning old COMBOARDs into some form of disk controller (IDE
or SCSI would be the easiest), but I never get past the napkin stage
of designing.  What would be far more practical would be an Unibus
ESDI controller, but I don't remember seeing too many of those in the
past (what I did see was "lots" of SMD for Unibus and SMD or ESDI for
Qbus - all popular for those that were happy enough with non-DEC

It all comes down to drivers.  2BSD I know can handle Emulex and other
controllers just fine.  I'm not as certain about Ultrix-32 (it seemed
to be heavily slanted towards a DEC system disk, at least).  I recall
a variety of releases of VMS drivers for SI and Emulex controllers, so
it would be handy, I'd say, to identify what OS and version targets,
seek out ancient driver install kits _then_ go looking for a suitable
controller, but I think in practice, it'll be a case of finding a $50
card and then looking for drivers.

It's this struggle that makes me start to envision what it would take
to turn a COMBOARD into a low-performance disk controller.  I say "low
performance" because no matter how one would reasonably hack on the
existing hardware, and though it has a Unibus DMA engine (the 18-bits
of the Unibus are  mapped into 1/4 of the memory space of the onboard
68000, so DMA cycles are as easy as a DBcc loop), it's programmed I/O
from the 68000 side, limiting the max transfer speed to about
200KB/sec.  You _could_ stick a disk on it, but it really was designed
as a communications controller.  Since you'd have to write the drivers
from scratch anyway, one might as well start with something that's
_meant_ to talk to disks.  I only keep coming back to the idea since I
have a stack of working boards on the shelf and I have 100% of the
engineering info on them (and all the rights).

Thinking of COMBOARDs, ISTR someone (more than one?) on the list found
a COMBOARD in a machine they picked up some time back. I am still
trying to recreate our old test/development environment with simh, but
I'm lacking in a way to bootstrap a simulated 11/780 with VMS 4.x.
Once I get around the issue, I have backup saveset files made from the
last days of Software Results I can restore - all of the source and
tools and textual docs are there, and I'd be able to "cut a tape" of
the install kit for a variety of OSes and COMBOARD products.  This is
assuming anyone still wants to talk HASP or 3780 from a real Unibus
box, of course.  That's what the board did, and it did do it well.
The disk-controller idea is just something I kick around from time to


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