Re: please help--tracks, sectors, VTOC, and disk geometry

["josephoswaldgg@hotmail.com" <josephoswald@gmail.com>]

Tracks on the Disk II are numbered from the outside circumference
(track 0) counting up toward the inner hub (track 34 dec). The sectors
had two sets of numbers: one encoded in the low-level bit markers of
the disk, and one used in software. The software sector numbers used by
DOS were not in consecutive order, but were "skewed" in an effort to
optimize speed: the time to process a disk sector meant it was
impossible to read the very next physical sector, until it came all the
way around again. I never looked at a disk mechanism to know which way
the disk rotated relative to the read-write head.

Using a VTOC that indicated an unusual sector ordering was useful to
reserve space for disk sectors "outside the control" of DOS. One neat
trick would be to create a disk that could boot ProDOS, but would
catalog under DOS. Each OS would have half a disk or so for files. Or,
a game program could use the "hidden" space for game data, protected
against accidental deletion.

Have you tried booting the disk image in an emulator?

The usual VTOC and catalog location was meant to be in the middle track
of the disk. I don't recall the default allocation of file sectors, but
I believe it started adjacent to the directory track. Beneath Apple DOS
probably has a description, but I lost my copy years ago. It might be
perfectly normal to find it in the state you describe.