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.
The way folks used to duplicate disks protected by custom head-positioning schemes was through a variety of track-by-track copying programs (Locksmith, Nibbles Away, and Penulticopy were the most popular IIR) that could be fed parameter files with custom instructions for head positioning/rotation speed to duplicate the data for a given piece of software.
These parameter files were generally created by the community, who raced to be the first to gain fame publishing the keys for whatever just released or impossible-to-crack software came out. For a brief time, there was a thriving underground of parameter file traders.
I knew of someone who'd actually compiled a book of parameters, got it printed at a local copy shop and would sell it for $16 at swap meets. He eventually got a C&D from the makers of Locksmith claiming that the parameters he was publishing were covered under their copyright (even though they were created by the community). Not sure if they actually had a legal case, but he wasn't about to find out.
The makers of Locksmith took a position which might be called "ironically consistent", as in: "We make a utility for breaking copyright, so, darn it, it behooves us to demonstrate deep ignorance of copyright!". :)
I used Nibbles Away and Locksmith, but never for disks that needed the parameters; just ordinary "garden variety" copying.
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.