[2] Apple and Commodore 64 copy protection schemes were extremely varied and creative because most of the floppy disk reading and writing was controlled by software (or firmware), not by hardware.
These copiers reproduced copy protected floppy disks an entire track at a time, ignoring how the sectors were marked.
Locksmith copied Apple II disks by taking advantage of the fact that these sync fields between sectors almost always consisted of a long string of FF (hex - all '1' bits) bytes.
Henry Roberts (CTO of Nalpeiron), a graduate student in computer science at the University of South Carolina, reverse engineered Locksmith, found the sequence and distributed the information to some of the 7 or 8 people producing copy protection at the time.
The next advance came from Henry Roberts' thesis on software copy protection, which devised a way of replacing Apple’s sync field of FFs with random appearing patterns of bytes.
The back and forth struggle between copy protection engineers and nibble copiers continued until the Apple II became obsolete and was replaced by the IBM PC and its clones.
This effectively nullified the efficacy of deliberate disk errors, non-standard track layouts, and related forms of copy prevention.
Super Kit/1541[4] was sold by Prism Software around 1986 written by Joe Peter who also did Wrap Speed and some of the VMax copy protection.
NIBtools is a modern (circa 2006) open source software that performs the same function, intended mainly for archiving data from old floppies that may be copyright-protected or damaged.