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

[Johnny Billquist]

"Ethan Dicks" <ethan.dicks at gmail.com> wrote:

> On Sat, Dec 27, 2008 at 1:29 PM, Bob Armstrong <bob at jfcl.com> wrote:
>>> Ethan Dicks wrote:
>>> 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.
>>  I've got cartridges, but I really, really, (_really_!) doubt that it'll
>> make your drive work.  RC25s were notoriously unreliable even when they were
>> new, and as unsealed (even the fixed platter is open to the air) drives they
>> just don't age well at all.  I've got two RC25 drives (well, maybe even
>> three but that's another story) and none will work.  I spent a couple of
>> weeks working on them once, and all will now try to spin up and then fault
>> with various error conditions (I've since forgotten the error codes -
>> sorry).
> 
> I've owned two 11/725s over the years.  As I've posted before, I've
> never had the problems with the RC25 that others report.  I know they
> are notorious, but _I_ never had one fail.  That being said, of
> course, the chances of mine working are now diminished merely because
> I've said something.  ;-)

:-)
I haven't even seen an RC25 in 20 years... But they worked back then. 
But then again, I was working at DEC at the time, and needed them for 
the work I was doing, so I guess had they failed, I would just have 
gotten another one. :-)

>>> 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),
>>  Another option would be to build something that plugs into the LESI (aka
>> Aztec) controller and pretends to be a disk.  That'd be way cool.  But I've
>> never seen any documentation on the LESI interface, either electrical or the
>> protocol, so I've no idea how hard that would be.  As long as the interface
>> remains undocumented, I'd guess "really hard".  And of course the LESI
>> interface wasn't very popular (it was only ever used for the TU81 and the
>> RC25) so the potential market, outside of you and me, is limited :-)
> 
> Yes... that would be an interesting way to go, but as you point out,
> lack of documentation makes that an unlikely path.

Don't the TK50 also use LESI?
Or did I just imagine that?

>>  The important thing is that whatever you come up with has to be close
>> enough to a standard MSCP controller so that you can boot it with the
>> standard DU bootstrap and so that VMB can talk to it.  Unfortunately some of
>> the third party SMD controllers weren't really MSCP compatible and needed
>> custom bootstraps and VMS drivers (we used to have an SI controller on a 780
>> that fell into this category) - those would be a problem unless a) you can
>> also recover the software (difficult), and b) they supported a 11/730 (even
>> more unlikely!).  The LESI approach at least avoids this problem.
> 
> Agreed.  OS driver support is always foremost in my mind when fiddling
> with 3rd party disks.  We always had to wait for SI to release driver
> patches for our SI9900 since a Fuji Eagle is not the same size as any
> DEC disk (in our case, they would patch the geometry table in
> DRDRIVER.EXE to "oversize" the RM05 entry since we didn't have any
> real RM05s on the system).
> 
> It sure would be nice to find a Unibus SCSI card that looked to the
> system like a UDA50 - i.e. - true and proper MSCP emulation.  I don't
> know if there ever was such a product, but the VAXBI ones I saw years
> later were $10,000 new.  :-(

There are/were several. I have a CDU-720/TM. That's CMDs Unibus version 
of the CQD-220. Very nice. Works about the same way as the CQD too.
I also have a Viking one, but that only talks TMSCP (but I'm pretty sure 
they did exist for disks as well).

>>  Of course if you only want to run Un*x then you have more flexibility :-)
> 
> True, and I _do_ care about Unix (2BSD for PDP-11 and Ultrix-32 for
> VAX), but I also care about RT-11 and pre-6.0 VMS.
> 
> Just thinking back to when I used to do this every day for a living, I
> don't recall there ever being an ideal solution, just solutions that
> fit enough criteria to be acceptable (Re: price-compatibility-capacity
> matrix).  If you had money, you paid for DEC disk.  If you had a no
> budget, you bought 3rd party and decided what features to give up (the
> ability to seamlessly install the OS and upgrade at will was almost
> always the first thing to go).
> 
> Not all of the "good old days" were as good as we'd like to remember.

Sure they were!
But as far as disks go, until good MSCP emulating controllers came out, 
it was always a headache with 3rd party disks and controllers.

	Johnny