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

Herb Johnson hjohnson at retrotechnology.com
Thu Feb 27 09:32:05 MST 2020

Well, I am distracted by a friend's serious illness today. And I don't 
wish to be drawn into arguing  with Jon Hales on speculative matters and 
certain matters of opinion. Jon otherwise makes good points about 
possible sources of difficulty. I'll focus on positive and actionable 

It's possible the various drives in use, have some variance, as Jon 
suggests. Those can be resolved in two ways. One, use different drives 
on the same computer and controller, format and write to and read from 
diskettes, and confirm those diskettes are all cross compatible. That's 
my rule-of-thumb standard for testing drives, which I've sold to others, 
without receiving complaints. Two, obtain an alignment diskette, attach 
an oscilloscope, and perform the tests supported by the diskette; those 
are computer-independent.

I now read carefully, Roger Arrick's actual message of 2/26. It's good 
to have experiential facts.

1) Roger suggests his MDS225 with its own drives, can read foreign CP/M 
8" SSSD diskettes "fine". That can be tested by sending him an arbitrary 
number of such diskettes. He says "it DIRs fine". That means tracks zero 
to several are readable.

I suggest running a CP/M file checksum program; that will force 
read/verifies to whatever tracks have files. The CP/M UG and SIG/M have 
a CRC or CRCK program. I"ve had "reads fine" but "checksum errors" occur 
under various circumstances.

Or, one might use "DU" or "DUU" (same distributions) and tell it "read 
the next sector" from start to end. That tests sector and track 
checksums but only reports persistent failures (or you notice the head 
steps slower and sector-reports are slower). My point is: flux physical 
density increases and disk media velocity decreases, on the inner vs 
outer tracks. One should read the whole diskette. Results could be 

2) Roger says, "My imagedisk PC [and its drives] creates 8" SSSD CP/M 
diskettes which can be read by other vintage systems". He cites a ISA 
controller, known for compatibility. Again: his total system can be 
tested by sending his *bulk erased*, then formatted and written 
diskettes, to be read by several other systems; in the ways I suggested.

Bulk erasing eliminates prior format information including consequences 
of misaligned writes. These matter more on 5.25-inch media due to 40/80 
track differences.

3) Roger offers an IMD file imaged from a "successfully read" CPMUG 
diskette. He says when he writes this file onto an 8" SSSD diskette on 
his PC system; said disk a) cannot be read on his MDS225+drives system 
but b) can be read on a local non-MDS+its_drives system.

In principle he can postal mail his MDS+drive written 8" SSSD diskettes 
to other people, see if they can read such diskettes, and if not (they 
might) determine the source of the failure.

As I and Jon I think suggested: Roger may wish to attach his Xerox 8" 
disk drives to his MDS225 system; attempt to read the various 8" SSSD 
CP/M diskettes he's produced and those produced by others; attempt to 
write new diskettes; and then reattach his "MDS225 drives" and read the 
Xerox-drive-MDS225 diskettes. Those results may be informative.

In summary: Roger may choose to obtain or provide diskettes to/from 
other people, to establish compatibility and or find errors. And Roger 
may swap drives on his system, to see if "errors follow the drive". One 
can posit that a particular system (computer+drives) is more or less 
compatible or forgiving of drive format or disk media, than some other 
system (computer+drives). That's also a choice.

I have a Heath/Zenith Z-100 (Z-121) S-100 system which operates a pair 
of 8-inch drives (I forget brand/model). I can run CP/M and MS-DOS (but 
not IMAGEDSK); Zenith provides a MS-DOS based diagnostic including a 
disk drive/controller diagnostic. I'm pretty confident, my 8-inch drives 
can read any number of diskettes from any number of sourced diskettes in 
8" SSSD CP/M format. I have several brands and models of 8-inch drives I 
can attach, and I've serviced drives for years with that system.

So if Roger chooses to contact me privately, we can arrange to 
physically swap various 8" SSSD CP/M diskettes. I'm not offering to run 
oscilloscope tests at this point, but a few swaps and the other testing 
I suggested, may be useful to him. If Roger wishes to buy an 8" 
alignment diskette, I can offer some to him.

Herb Johnson
Herbert R. Johnson, New Jersey in the USA
http://www.retrotechnology.com OR .net
preserve, recover, restore 1970's computing
email: hjohnson AT retrotechnology DOT com
or try later herbjohnson AT retrotechnology DOT info

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