[Info-vax] Assistance needed!! working RM05 drive and VAX needed for proje

[Rich Alderson]

"terry-... at glaver.org" <terry-groups at glaver.org> writes:

> On Thursday, September 28, 2023 at 5:31:07=E2=80=AFPM UTC-4, Johnny Billquist wrote:

>> I've been reading the RM02/RM03 manuals, and I can't find any=20
>> documentation on any backplane jumper for such a purpose. There are
>> jumpers for drive type and serial number, but that's about it as far as
>> I can find.

> I assume you mean in the Massbus controller in the bottom of the drive.
> The actual drive logic cage has not very many not very big not very bright
> cards. As I recall, maybe 5" x 5". I modified a couple sets of drive cards
> to change the upper cylinder limit. I was subcontracting data recovery
> and they'd send me crashed-but-cleaned packs and tell me "don't go past
> cylinder X" when doing the recovery.

The DCL ("DEC control logic") on an RP06 is about a dozen hex height boards in
a special card cage on the side.  The little 5"x5" cards in the top of the
drive are Memorex (the OEM).

> I don't know why DEC didn't do Massbus disk strings the way they did
> Massbus tape strings - you can't have multiple data transfers going at
> the same time on the Massbus anyway, and the Massbus supported
> per-drive things like "Seek Complete" already. I guess customers that
> cared about over-paying for drives just bought the CDC versions and
> 3rd-party controllers.

I don't understand what you mean here.  We had strings of up to 8 RP07 or RP06
drives on our DEC-20s.

> Massbus is weird. Somebody saw IBM 360 bus/tag cables and went
> "This would be a good idea - how can we make it bizarrely different?"
> Trivial example - the RP07 is logically an RM device, not RP. Surprised
> a bunch of early customers who tried adding one to a string of RP06
> drives.

Not sure I ever saw more than one RP06 on a DEC-20 with RP07s, since only one
was needed for the 11/40 front end.  It wouldn't make sense to daisychain the
big drives through that any way.

-- 
Rich Alderson					  news at alderson.users.panix.com
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									--Galen