27 Dec
2008
27 Dec
'08
3:55 p.m.
"Ethan Dicks" <ethan.dicks at gmail.com> wrote:
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?
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).
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
On Sat, Dec 27, 2008 at 1:29 PM, Bob Armstrong <bob
at jfcl.com> wrote:
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. :-)
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). 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 :-) 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. :-( 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.