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

["Bill Garber" <willy46pa@comcast.net>]

"josephoswaldgg@hotmail.com" <josephoswald@gmail.com> wrote in message
1109296218.398727.136370@o13g2000cwo.googlegroups.com">news:1109296218.398727.136370@o13g2000cwo.googlegroups.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.

If I could dig out my copy, I could scan in the relevant
pages concerning the actual disk construct, but, it would
take me hours to find it in the shape of my present mess
of Apple II, Atari, Commodore collectibles.

Apple II Forever, Apple II Together
Bill @ GarberStreet Enterprizez
Web Site - http://garberstreet.netfirms.com
HOME OF THE RAM-4-GS
Email - willy46pa@comcast.net