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Old 22 December 2013, 19:17   #35
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Join Date: Dec 2013
Location: Lake Havasu City, AZ
Posts: 500
Originally Posted by mr.vince View Post
Funny thing, haven't been able to find it on TOSEC either. Since this is all hardware dependent, and you seem to control it... why not put it up?
I have no idea what TOSEC is.

I am in the process of putting all of my original C64 and Amiga software on my website. So, it will be there at some point. I am packaging the original SYBILs, with original disks for resale too.

I am not sure if trackdisk.device ever actually used the precomp. I have a disassembly of it somewhere. I know that Amax disk's didn't. None of my stuff ever needed precomp, and the age old argument about disks going bad without using precomp is ridiculous. I have hundreds of copies of protected disks (along with their originals) from the late 80's/early 90's and every single disk - even those with protection on track 79-81, still load just fine. Yes, the write precomp (what I call post read normalization) does help eliminate the bit shifting that is more common at higher denisty, but it certainly is not a requirement for longevity. The only thing it is good for really is generational copies.

Yes, there were quite a few Amiga programs that used the GCR mode. The disk-2-disk Mac copier pulsed the Amiga's motor to reduce the drive speed. It wasn't great, but with numerous retries you could get a variable speed Mac disk to read (no writing). I made SYBIL for this, which did support reading and writing of Mac disks. I also made AMIA, which was a single chip PEEL based drive interface that allowed you to attach a real Mac floppy to the Amiga and read/write Mac disks, all using the GCR mode.

I don't recall the games that were copy protected with some Mac tracks put on them, but they existed. Supercard Ami could copy Mac disks, besides Atari ST, Amiga, 5.25" PC, C64, Atari 800, etc. disks. It was not uncommon for game manufacturers to try to use the same protection between their Mac, Amiga, Atari ST counter parts. For example, Dungeon Master for the Amiga has the exact Atari ST track on it for protection. Companies that had both Mac and Amiga versions often times used the Mac protection because the Amiga could read GCR.
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