From: Nicolas Welte (welte_at_chemie.uni-konstanz.de)
Date: 2002-07-10 18:02:37
Bryan Pope wrote: > > And thusly Nicolas Welte spake: > > > > track drives, not the old 40 track ones (because the 1541 also has 80 tracks, > > even if it uses the head from a 40 track drive). > > > > So is it possible to move the 1541's head as if there were 80 tracks? Yes. The tracks between the 40 normal tracks (numbered 1 to 40) are called half-tracks, and are numbered 1.5 to 40.5. The DOS of a 1541 steps onto these half tracks when a read error occurs on the full track position. Half tracks are also said to be used as a copy protection (note that it is impossible to use both a full track and one or two of its adjacent half tracks, the previously written track would get overwritten because of the 40 track r/w head). But you can use e.g. track 23, track 24.5 and track 25.5, and test the copy for correct positions of the tracks. A simple copy program would probably move the half tracks back to the full track position. An advanced protection scheme could just use a single sector or only a few bytes on the half track, at a position that has only gaps on the full track. This would also need track synchronisation, which the 1541 cannot do easily, it lacks an index hole sensor. Nicolas Message was sent through the cbm-hackers mailing list
Archive generated by hypermail 2.1.4.