I'm still more impressed by the schemes that prevent you from just copying tape-to-tape or disk to disk. I remember on the C64 some games deliberately put read

I'm still more impressed by the schemes that prevent you from just copying tape-to-tape or disk to disk. I remember on the C64 some games deliberately put read errors on the tracks, which most copy programs would ignore. If you did a disk-to-disk copy, the duplicate wouldn't boot because it was looking for the read error. I figured out I could use a sector editor to read the error from the original disk, swap them out and then write it to the duplicate - which then worked correctly.