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8" Disks encoding?

Posted: Wed Aug 07, 2019 9:01 pm
by auron
I have dumped some 8" CP/M Disks sucessfully - they were FM encoded, 128 Bytes per Sector and 26 Sectors per track, at 360 rpm.

Yet, the majority of the disks from that stack fail to decode. Data still seems to be there, as there are well defined bands in the graph, but I can't figure out what the encoding might be.
I attached the consistency graph of a sample track, they all look more or less like it.

I tried FM, MFM, and GCR, different sector sizes.. nothing.

Anyone has a hint for me?

Re: 8" Disks encoding?

Posted: Thu Aug 08, 2019 1:16 am
by ZrX
Those 4 bands in the graph mean that encoding is very likely to be the somewhat rarely used MMFM/M2FM which DTC does not currently decode.

I've decoded few such dumps for another user with my own experimental tool successfully.

Re: 8" Disks encoding?

Posted: Thu Aug 08, 2019 8:42 am
by auron
You're sort of forcing the follow up question ;-)

Any chance you are willing to do that work for my dumps, or share the experimental tool?

Re: 8" Disks encoding?

Posted: Sat Aug 10, 2019 12:31 am
by ZrX
Can you upload the raw files of one dump to a sendspace or some similar place and post or PM the link so I can check if the format is the same or if I need to write some different decoding?

Re: 8" Disks encoding?

Posted: Sat Aug 10, 2019 6:44 am
by auron
Thanks a lot! - I sent you a PM.