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. XEMAG 2.0 (the Activision variety of this protection) is skewed about 1/2 track between 35 and 36 (and some amount between 34 and 35 also that doesn't appear to be checked). I noticed years back that this protection boots if the drive motor is slowed down to 298.5 or lower (within reason) no matter what the skew. I guess something about how their timing check is setup allows this to pass. -- - Pete Rittwage C64 Preservation Project http://c64preservation.com Message was sent through the cbm-hackers mailing listReceived on 2009-03-23 02:59:40
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