Commodore 1541: Encyclopedia II - Commodore 1541 - Copy protection by read error

Commodore 1541 - Copy protection by read error

Early copy prevention schemes deliberately introduced read errors on the disk, the software refusing to load unless the correct error message was returned. The general idea was that the inbuilt disk copy command was incapable of copying the errors. When one of these errors was encountered, the disk drive (as do all disk drives) would attempt one or more re-read attempts after first resetting the head to track zero. Few of these schemes had much deterrent effect, as various software companies soon released 'nibbler' utilities that enabled protected disks to be copied.

The later 1571 drive (which was 1541 compatible) incorporated track zero detection and was thus immune from the problem. A third party fix for the 1541 appeared where the solid head stop was replaced by a sprung stop which gave the head a much easier life. Also a software solution which resided in the drive controller's RAM, prevented the re-reads from occurring, though this could cause problems when genuine errors did occur.

Adapted from the Wikipedia article "Copy protection by read error", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki