8 inch disks - help needed identifying format

Eric Smith spacewar at gmail.com
Wed Aug 3 12:26:53 CDT 2016

On Wed, Aug 3, 2016 at 3:19 AM, Rik Bos <hp-fix at xs4all.nl> wrote:
> It is a HP disc, probably for the hp 9845/35 series.
> H tells you the drive type (9895A), 8 the controller select code, 0 the drive address, 1 the unit address (second disc in a unit, first disc will be 0).
> Probably the disc will contain a large fata file of 1188 blocks, may be it’s a database can’t say much more of it. To determine the data itself you need to know the first record of the file,they will tell the kind of data in it.

If it's a 9895A disk, and if it is double density, then the 9895A is
the only drive that can read the disk in the normal way, because HP
used their own unique M2FM format for that.

Of course, a flux-transition reader like Catweasel or DiscFerret can
be used to archive it, though AFAIK there's not yet any software that
understands 9895A format. The 9895A documentation doesn't give enough
detail on the format, so some reverse-engineering of the format
details would be needed to write suitable decoding software.

I'm currently working on a Python program to decode Intel M2FM format
(used for double density 8-inch with SBC-202 controller on MDS 800,
Series II, Series III) from flux transition data. The Intel M2FM
format is reasonably well documented.

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