The Apple II disk drives featured head movement that was operated by programmed I/O. For increments of a stepper motor were required to go from one track to another. This made it possible to write data in quarter track increments, giving rise to one copy protection scheme.
A conventional track-by-track disk copy program would not correctly copy data written in a spiral pattern using quarter track increments.
There were also schemes whereby tracks were written at a different speed. The logic-state-sequencer state machine for shifting bits from the head would still read the data correctly, but the program could tell a copy made at a conventional speed from the genuine article, due to the different size and content of the gap.
Programs that did this sort of thing would tend to have to be cracked by removing all the checks, and replacing their disk loading routines with conventional ones that read ordinary tracks that are copyable with any disk copying utility.