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On Thursday, September 28, 2023 at 5:31:07 PM UTC-4, Johnny Billquist wrote:
> I`ve been reading the RM02/RM03 manuals, and I can`t find any
> 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.
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 remember when Emulex came out with a new generation of SMD
controller - UD33, perhaps. I thought the biggest "win" on the new card
was getting rid of the high-speed processor logic in favor of dedicated
gate arrays. I asked my contact at Emulex (I was field testing) what
they thought the most important thing was. They said "controller-
resident diagnostics".
> By the way, it`s kind of strange to talk about different "controllers".
> Of course they are different. The PDP-10 have a very different massbus
> controller compared to a PDP-11 or a VAX. But they all talk massbus, and
> the devices on the massbus itself is sortof agnostic to the machine word
> size.
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.
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