One way is to arrange things such that the read doesn't fail but is non-deterministic. The game reads the same dodgy disk sector multiple times, and checks that

One way is to arrange things such that the read doesn't fail but is non-deterministic. The game reads the same dodgy disk sector multiple times, and checks that the results are not the same on every read. A normal disk copy will read that sector once from the target disk and write the result to the destination disk. Any reads from the destination disk will be deterministic, and trigger the copy protection. See http://dmweb.free.fr/?q=node/210 http://dmweb.free.fr/?q=node/210 for the most famous implementation of this (Dungeon Master).