#10 single-sided vs. double-sided detection

[David A. Gatwood]

A fix was made to allow DSDD disks that were formatted as 400k
to be reformatted as 800k. This fix, unfortunately, will also allow
SSDD disks to be formatted as 800k. It may fail, of course, but
this is a bug. The code should check to see if there's an index
mark on the back side of the disk. If there is no index mark, it's a
SSDD, and the driver should report the capacity as 400k. If there
is an index mark, it's DSDD, and the driver should report the
capacity as 800k.

The flip-side of this bug is that DSDD disks formatted 800k cannot
be reformatted as 400k. The driver correctly enforces this.
However, an unformatted DSDD disk with no address marks on the
back side can be safely formatted as 400k. It is sufficient to
check for address marks on track 0. If address marks are found
on the back side on track 0 (even if the front side is completely
hosed), then the only valid capacities are 720k and 800k. If no
address marks are found, the valid capacities then become 360k,
400k, 720k, and 800k, although the driver currently only supports
the last three.

[David A. Gatwood]

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Really low priority. 400k, 720k, and 800k formatting have to WORK first.
:-)