Bit nibbler

Background

Software piracy began to be a concern when floppy disks became the common storage media. Jerry Pournelle wrote in BYTE in 1983 that 'CP/M doesn't lend itself to copy protection' so its users 'haven't been too worried' about it, while 'Apple users, though, have always had the problem. So have those who used TRS-DOS, and I understand that MS-DOS has copy protection features'. 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.

Pournelle disliked copy protection and, except for games, refused to review software that used it. He did not believe that it was useful, writing 'For every copy protection scheme there's a hacker ready to defeat it. Most involve so-called nybble copiers, which try to analyze the original disk and then make a copy'.

By 1980, the first 'nibble' copier, Locksmith, was introduced for the Apple II. These copiers reproduced copy protected floppy disks an entire track at a time, ignoring how the sectors were marked. This was harder to do than it sounds for two reasons: firstly, Apple disks did not use the index hole to mark the start of a track; their drives could not even detect the index hole. Tracks could thus start anywhere, but the copied track had to have this 'write splice', which always caused some bits to be lost or duplicated due to speed variations, roughly in the same (unused for payload data) place as the original, or it would not work.

Secondly, Apple used special 'self-sync' bytes to achieve agreement between drive controller and computer about where any byte ended and the next one started on the disk. These bytes were written as normal data bytes followed by a slightly longer than normal pause, which was notoriously unreliable to detect on read-back; still, you had to get the self-sync bytes roughly right as without them being present in the right places, the copy would not work, and with them present in too many places, the track would not fit on the destination disk.

Commodore 64

Part of the Fast Hack'em disk copy software was a nibbler used to produce copies of copy protected Commodore 64 commercial software. When using the nibbler, disk copying was done on a very low level, bit-by-bit rather than using standard Commodore DOS commands.

This effectively nullified the efficacy of deliberate disk errors, non-standard track layouts, and related forms of copy prevention. Super Kit/1541 was sold by Prism Software around 1986 written by Joe Peter who also did Warp Speed and some of the VMax copy protection. It included many different copiers like a Normal Copier, Nibbler, File Copier, Super Nibbler, Disk Surgeon, and disk Editors.