Re: "Fat tracks" are not really fat tracks

From: Pete Rittwage <peter_at_rittwage.com>
Date: Wed, 3 Apr 2013 13:57:32 -0400 (EDT)
Message-ID: <59426.10.2.0.31.1365011852.squirrel@rittwage.com>
On Wed, April 3, 2013 9:08 am, Antitrack@networld.at wrote:
>
> Zitat von Wolfgang Moser <womo@news.trikaliotis.net>:
>
>> Hello Pete,
>>
>> Pete Rittwage schrieb:
>> > Hi guys,
>> >
>> > With the help of "TeaRex" on my forum, I added a simple way to
>> > read/write disk images using the index hole sensor built into the
>> 1571.
>> >  Through this addition, a revelation occurred.
>> >
>> > We had always assumed (since the 80's) that the Electronic Arts' "fat
>> > tracks" protection had 2 tracks (34 and 35) perfectly aligned.  I
>> added
>> > the index hole code and wrote out the disk perfectly aligned to track
>> 0
>> > and thought it was beaten.  :)
>> >
>> > Well, it turns out this assumption is *not* true.  When reading
>> against
>> > the index hole, track 35 is actually skewed back 1/4 track or so on
>> all
>> > the original disks.  If I write it back out skewed in this way, it
>> > boots.  These were never "FAT" tracks at all, just a specific track
>> skew
>> > between two identical copies of a track.
>
> That makes perfectly sense, since the time to move the stepper from
> Track34 to
> Track35 is about the same time as you need to read 1/4 of a track.
>

I ended up being wrong about this.  I had an error with my tools that
fooled me.  :)

-
Pete Rittwage




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Received on 2013-04-03 19:00:06

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