floppy disk

floppy disk

After discussions in a Facebook group I thought I’d write something more on copy protections on disk.

The general starting point is the disk is a sheet of magnetic media put into a mechanism to read it. The mechanism has a stepper motor that aligns the read head to different circles of the disk (tracks). The track is then split into different sector. Each sector has a header and a tail before and after the data. The formatting of a sector is on the c64 bult into the Disk OS. What should also be said is that on the c64, the sectors are placed in sequence but where on the track they are placed is random. They are placed where the formatting routine chose to start. This is unlike for example PC disks, where the small home near the center kept track of where on the disk the sectors where placed.

The layout of the disk is established during the low level formatting, and the disk is then ready to hold files and sector data that is copied to it.

Software companies were keen that you shouldn’t copy their disks. The common method was then to create deliberate format errors and look for these in the running program.  If the errors weren’t there, then this indicated that the program was a copy and the software would refuse to run (the more devious programs adapted the gameplay to make it unplayable, but these examples are really few).

Deliberate errors cannot be copied using standard copy programs (including the one on the demo disk of the 1541 disk drive). Either the read fails or at least the error is not reproduced in the copy. Now what?

Well, there are a few different lines of development:

  • More cunning copy programs that were able to detect errors and reproduce them. We call these programs nibblers. The copy is the same as the original – including all errors, and also isn’t copyable using a standard DOS copier
  • Cracking, where a cracker removes the copy protection code (and generally tags the copy with his or his groups name)
  • More cunning copy programs that creates an error free (and copyable) version, by making modifications to the original, disabling the eror checking in the original. These copy program used “parameters”, ie the little instruction on what to modify on the game to make it work. The parameter is basically also cracking the game, but without the tagging.

The complexity of the errors and checking of the errors developed, and after a few years you had games that could be read on the 1541 but they couldn’t be copied with any nibbler as the 1541 wasn’t able to reproduce the structure. Writing with an industrial copier and adding tracks that the 1541 could reproduce was possible and then the c64 community relied on cracking and parameters to copy their games. (Today you can use SuperCopyPro or KryoFlux thyat can read all disk on the lowest level. Converting this to G64 format, it’s readable with some of the emulators).

So if you have an old original that you want to play, but you want to play the copy not to wear the original, then either get a nibbler that can copy it, or find a copy program that has a relevant parameter or pick up a cracked version.

Further reading:

http://www.c64copyprotection.com/

https://c64preservation.com/dp.php?pg=protection

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