Matthew Russotto wrote:
In article <Ap-dnZrH5JYZ76DYnZ2dnUVZ_u-dnZ2d@comcast.com>, Michael J. Mahon <mjmahon@aol.com> wrote:Matthew Russotto wrote:In article <aJKdnTNJ_tZU6qXYnZ2dnUVZ_o2dnZ2d@comcast.com>, Michael J. Mahon <mjmahon@aol.com> wrote:There is the potential for writing a track with ambiguous nibble sync, in the sense that it could be read with nibbles synced in more than one way. I don't know of any program that uses such a technique, but it ispossible.I ran into one such, the driver disk for a speech recognizer. It didn't seem to have any self-sync nybbles. It was slow as heck running its modified DOS (which I presumed, but didn't prove, tried every possibility until sectors started reading). Since it used a normal DOS filesystem, I was able to copy it file by file to a regular disk, using a cassette tape for an intermediary.A very creative solution! That would be a natural for a "swap controller" that swaps between the protected RWTS for reading and a normal RWTS for writing.Yep, that's what I tried, but it didn't work. I could read sometimes, but not at all reliably. My best guess is that they'd modified the code calling the RWTS to change the timing of re-tries in ways which would semi-reliably change the starting bit to something else on the retry. But that's when I had the cassette-tape idea and I didn't investigate further -- working with that disk was painful due to its speed.
I understand. I had the same problem with a disk that used a highly modified version of DOS, so that RWTS entry points were different, making a swap controller a mess. -michael NadaNet networking for Apple II computers! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it's seriously underused."