Re: Disk II 70 Tracks

[mjmahon@aol.com (Michael J. Mahon)]

In article <D--dnYLTZbfdKMijXTWQlg@giganews.com>, "Bryan Parkoff"
<BParkoff@satx.rr.com> writes:

>    Previous post states that odd tracks are not used.  Do you know what odd
>tracks contain garbage data?  Someone said that we may be able to modify DOS
>3.3 to handle 280KB instead of 140KB.  Is it true that Disk II Family has an
>ability to read/write both odd-even tracks in full that it may be capable to
>handle 280KB.  Is it possible that even tracks might overwrite odd tracks
>that will not be supported?  Please advise?

You misunderstand.

There are no "odd tracks".  There are odd numbers of steps from the home
(track 0) position, since all actual disk tracks are an even number of steps
from home.  The odd step numbers correspond to "half tracks", and they,
as you might expect, are overlapped by the "normal track" positions.

Put another way, the width of the head is just a little less than one track,
or two head position steps.  So there are no "extra" tracks between the
official tracks.  Half-tracks are well-known because some copy-protection
schemes used non-standard stepper postioning to write data a half-track
off from the normal positions, so as to confuse would-be copiers (who
were, naturally, confused for about two hours before figuring it out ;-).

It is expedient in RWTS to account for head position in "steps" instead
of "tracks", since it is actually doing the stepping.

-michael

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