Subject: Re: Suggested change to add volume numbering to .dsk disk image files
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From: russotto@wanda.vf.pond.com (Matthew T. Russotto)
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Date: Tue, 29 Aug 2000 02:12:53 GMT
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In article <39aa4da7$0$780$7f31c96c@news01.syd.optusnet.com.au>,
Thug <mhurwood@dingoblue.nospam.net.au> wrote:
}"Joseph Oswald" <jaoswald@is06.fas.harvard.edu> wrote:
}>
}> > Plus, with DOS 3.3 and compatible formats, could the emulator not pick
}up
}> > the volume number from the VTOC? (Track $11, Sector $0, Byte $6. I don't
}> > know if there's a similar record in ProDOS.) Protected disks or disks
}with
}> > their own custom DOS are still a problem, of course...
}>
}> I think that the volume number in the VTOC actually is *unrelated* to
}> the volume number encoded in the sector address fields. I seem to recall,
}> perhaps in the _DOSTalk Scrapbook_, some discussion which indicated
}> that DOS 3.3 itself made no effort to properly initialize this value
}> before formatting a disk.
}
}Never heard of that before! It's certainly not mentioned in "Beneath Apple
}DOS", which is where I get almost all my knowledge of DOS internals.
}
}Just goes to show, even 20 years later I'm still learning stuff about the
}Apple ][.

Don't "learn" this fact; it's not true.  The code which initializes
the VTOC volume number is at AE96 in a 48K machine booted with a DOS
3.3 master. 

AE96- LDA $B5F9
AE99- EOR #$FF
AE9B- STA $B3C1

B5F9 is the location of the 1s-complement of the volume number in the
file manager work area.  B3C1 is the location of the volume number in
the VTOC buffer.  This is done before the VTOC is written for the
first time.



-- 
Matthew T. Russotto                                russotto@pond.com
"Extremism in defense of liberty is no vice, and moderation in pursuit
of justice is no virtue."