>Tony Duell wrote:
> > >This is a RQDX3 ESDI hard disk controller.
> > RQDXn is not ESDI at all.. it is MSCP.
> > Megan
> Gentry
> Come again?
> ESDI is a drive interface, MSCP is a host-side command set (it's not even
> an interface -- you can have MSCP controllers for Unibus, Qbus, etc).
> I can't see how the fact that a controller accepts MSCP commands from the
> host means that it can't control ESDI drives (although, IIRC, the RQDX
> controllers did not -- they worked with ST506/ST412 interfaced drives)
Jerome Fine replies:
If I can add a comment, might I suggest that part of Megan's confusion
is that while many 3rd party manufactures did produce ESDI disk controllers
(if pressed very hard, I can probably think of about a dozen different ESDI
models from Dilog, Emulex and Sigma to name just 3 companies) all of which
also used MSCP as far as the Qbus interface to the PDP-11 was concerned,
DEC never did bother. Thus, maybe Megan became used to thinking of the
RQDX3 an MSCP interface - which it is - rather than the actual MFM
hardware interface.
In addition, not only DEC (although DEC was probably last to do so) but also
all of the above named 3rd party manufactures also produced controllers
(more correctly call host adapters) which were a SCSI hardware interface
along with the MSCP command set.
And of course, many of those 3rd party manufactures produced controllers
which accepted MFM drives which also used MSCP.
Finally, there were also controllers which handled SMD drives that also
used the MSCP command set.
Where Megan might have become confused was that the RQDX1,2,3 from
DEC accepted only a trivial number of MFM hard disk drives for which DEC
charged "interesting prices" - the markup was about 1000% - whereas the
3rd party companies accepted a wide range of different MFM drives, ESDI
drives and SCSI drives although with the SCSI host adapter from DEC (RQZX1)
probably all SCSI hard drives were allowed - Megan can you verify that?
NOTE: As others have pointed out (implicitly) any given controller with
a specific interface (MFM, SMD, ESDI and SCSI) required a hard disk
drive which was built to use that interface.
And last but not least, the RA81 type drives probably also used an MSCP
interface, but I can't remember the controller. Also, the very last and
probably
least was the RC25 drive from DEC (probably the worst hard drive that DEC
ever produced from what I have heard from others - never had the problem
of having one myself) which also used MSCP.
Is the above TOO MUCH? There is probably more I have missed as well
like the Unibus controllers and host adapters. Plus, most, probably all of
the
controllers and host adapters can also be used with a VAX of the appropriate
hardware backplane which also has a VMS device driver that uses MSCP
as well.
Sincerely yours,
Jerome Fine
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Received on Mon May 06 2002 - 22:16:05 BST