[Intel-devsys] IMAGEDISK for MDS 8" SSSD disks

Roger Arrick Roger at Arrick.com
Wed Feb 26 17:48:16 MST 2020

I've collected the evidence that there is something picky about the MDS II
internal SD drive controller (8271) causing an incompatibility with IMD (Imagedisk).

My MDS225 has an internal SD drive (E:) and 2 external DD drives (A:,B:)
using the standard intel DD board pair.
This is a nicely working system (after much work).
I boot the MDS225 into CPM 2.2 using the external DD drive.

Insert a CPM User group disk 8" SSSD disk (unknown origin) into E:.
It DIR's fine.

Now, I have a working imagedisk PC setup that successfully creates 5.25 SD disks 
as well as 8" SD disks which can be read by other vintage systems.
This PC uses the Adaptec AHA-1542CF (820778L) because it will write SD.

I take this CPMUG1 disk and read it using IMD.
Reads fine and saves as CPMUG1.IMD.
This file is available at http://www.rogerarrick.com/misc/CPMUG1.IMD

I then write a new disk using IMD named CPMUG1R.IMD with the CPMUG1.IMD file.
This file is available at http://www.rogerarrick.com/misc/CPMUG1R.IMD

This new disks which was duplicated through IMD will not read on the MDS225.
But it will read on a XEROX 820II CPM system.

Maybe it's something in the format or R/W gap settings.  I've tried a few 
different values with no success.  It would take a lifetime to try all 

This is mostly curiosity for me.  I was hoping to use my MDS225 as a standard 
CPM workhorse because I love it but this is a show-stopper.  I'll be switching 
over to the Xerox 820II - it's a boring, but solid and well-documented CPM sys.

Roger Arrick
Roger at Arrick.com
Tyler, TX

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