If you can use IMD to format both FM and MFM at 500Kbps on your 242--and
"Analyze" reads the format okay, your SCP disks aren't probably standard
IBM 3740 or System/3 type diskettes. They could be in a proprietary
recording format, such as Intel MMFM or Futuredata GCR.

On Wed, 9 Aug 2017, Richard Cini via cctalk wrote:
Thanks Chuck. The Gazelle uses the Tarbell DD controller which uses a 1793 which I believe is 3742 and s/34 compatible.

The [WD] 1793 is normally used for "standard" FM and MFM formats
(What I call "IBM/WD Stle formats", and that I think Chuck called "IMD formats")

BUT, it could be used for some OTHER formats that the NEC-style FDC can't handle, since unlike the NEC-style chips, the WD-style chips have the capability of a "track write"/"track read", with seriously different sector header structures.
Not enough diffeernt to do GCR, but maybe enough to do Amiga?

The NEC can do a multi-sector read/write, but that isn't the same, and it can't do ANYTHING other than "IBM/WD-style" formats.

PC normally uses an NEC-style controller, and that is the only type that the BIOS supports. At one point, there was an after-market WD-style controller with device driver support, but the added capabilities weren't enough to make it a market success. If anybody has one, it has the capability of reading a number of disks that the NEC can't.

My naming convention is flawed. I think that at one point Western Digital made an "NEC compatible" controller, that isn't what I call "wd-style"

Grumpy Ol' Fred                 ci...@xenosoft.com

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