Stripping an RA80

Tony Duell ard.p850ug1 at
Sun Jan 8 12:31:00 CST 2017

On Sun, Jan 8, 2017 at 6:20 PM, Robert Armstrong <bob at> wrote:
>>Tony Duell <ard.p850ug1 at> wrote:
>>Well, actually I think you own an R80 but don't know it :-)
>>As I understand it, the R80 had the sort-of SMD interface. 2 cables
>>(60 and 26 wires). It's not SMD, there are significant differences, but anyway.
>   Can't speak for it being an SMD interface, but the rest of this is correct.  And as tony

It's somewhat SMD-like, but it's not SMD. Some of the signals have the
same names
(like the control signal bus from controller to drive being called
'Tag') but you can't
plug an SMD drive into the 11/730 IDC. One oddiity is that the SMD
drive's select
lines are inputs to the drive (as you'd expect), on the R80 the lines
are outputs from
the drive giving the coding of the ready lamp cap (which sets the unit
number like
an RL02). I've not looked into making an interface between the 11/730 IDC and an
SMD drive, I might have to if the R80 proves unrepairable.

> said, the R80 was used only in the VAX-11/730 with the IDC.  The IDC, with the help of
> the CPU microcode, turns the R80 into an MSCP drive and also controls up to three
> RL02 drives at the same time.  FWIW, you can put an R80 HDA in an RA80 drive and
> vice-versa without needing to reformat.  Don't know if that's true for the RM80 - I've never
> actually used one of those.

I've always felt that the RA80 is the 'oddest' member of the family.
As a result I suspect
an RM80 HDA will swap with the others and vice versa, but I've not
tried it. The RM80
manuals aren't on Bitsavers.

> I have an 11/730 in the garage with the IDC and R80 drive.  I've got lots of spares for the
> R80 drive itself, but only one HDA and that one is unusable due to too many errors.
> Fortunately I also have a UDA-50 and two more RA8x drives in the machine so it's still
> usable.  It boots just fine from the UDA-50, but I'd love to restore the original drive.

The RA81 and RA82 HDAs seem quite different. They have more heads for
one thing, but
I get the feeling that the servo system is quite different. One manual
suggests not only do
they have the dedicated servo surface, but also embedded servo
information on the data
surfaces. AFAIK the R80, etc only has the dedcated servo surface.

The servo PCB seems to be the same in the R80 and RM80. That for the
RA81 is a lot more
complex with a microprocessor on it.

I had wondered if you could kludge an RA81 or RA82 HDA into an R80, I
think it would be
very hard.

>   If anybody has an R?80 HDA that they'd be willing to part with, let me know!

Not only am I the wrong side of the Pond, but the HDA is one part I am
keeping from
the RA80, no matter what I do with the rest of it. I don't know if
it's good, of course, but
if it is it will be kept as a spare for the R80.

The HDA is the only major unit I can't repair (yet!).


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