RQDX3 disk image for Gesswein's MFM emulator

Jerome H. Fine jhfinedp3k at compsys.to
Wed Aug 24 21:46:24 CDT 2016

 >Charles Dickman wrote:

>I am looking for an RQDX3 compatible disk image for Dave Gesswein's
>MFM disk emulator. I don't have a functional disk to image and the
>ZRQCH0 won't cooperate.
I suspect that I don't really understand your question, but maybe the
following information might help.

For both of the PDP-11 emulators that I have used, Ersatz-11 and SimH,
the disk image for an MFM hard drive is just a file in the hard drive under
the operating system under which either Ersatz-11 pr SimH is being run.
In my case, that is usually Windows 98SE although on a few occasions
I have also used the 32-bit Windows XP.

In addition, the original MFM DEC hard drive on which any of those
disk images were based were totally independent of which DEC
controller, RQDX1, RQDX2 or RQDX3, was actually used.  And
while the emulator might provide information which suggests that
an RQDX3 is being used, the actual disk image on the hard drive
would still be the same.  On the other hand, I I have never tried to
run ZRQCH0 under either emulator, so there might just be some
aspects that I am not aware of.  But to support my experience, if
I have an RK05 disk image on the same hard drive (of 4800 blocks),
I can also use that identical file as a disk image for the MFM emulator
for both Ersatz-11 or SimH as if it was connected to an RQDX3 in
the DEC hardware world EXCEPT that, of course, that disk image
would then appear as a very small MSCP device of just 4800 blocks
as a DU device under the Ersatz-11 or SimH emulator.

I am not sure if I explained myself correctly or sufficiently.  I am just
trying to say that, in my experience, a disk image of an MFM drive
in the DEC PDP-11 world (specified since you mention ZRQCH0
which run on a PDP-11) on the hard drive for use under an emulator,
such as Ersatz-11 or SimH, is identical to most other disk images for
any other DEC, in particular for those disk images which don't have
extra data to handle the disk drive blocks.  That means that there are
some extra blocks for RL01 / RL02 disk images, but not for many
others and, in my experience, that has included DEC MFM hard

I hope that the above information is helpful.  On the other hand,
Dave Gesswein's disk emulator may handle disk images quite
differently and require extra blocks such as what an RQDX3
requires and which are probably different from what an RQDX2
uses.  In that case, I don't know how you might create the disk
image that Dave Gesswein's emulator requires.

Jerome Fine

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