×

Announcing: Slashdot Deals - Explore geek apps, games, gadgets and more. (what is this?)

Thank you!

We are sorry to see you leave - Beta is different and we value the time you took to try it out. Before you decide to go, please take a look at some value-adds for Beta and learn more about it. Thank you for reading Slashdot, and for making the site better!

Comments

top

The Problems With Game Copy Protection

msbsod Re:I remember using Locksmith and such in the 70's (439 comments)

The Apple II was (and still is) also good to produce copy-proteced disks for computers with a floppy controller of the Western Digital family. Format a track with the WD controller, put the floppy into an Apple, write the same track with the Apple "controller" (it is actually just a shift register) for a brief moment and interrupt the procedure so that only a small fraction of the track gets overwritten. The Apple does not care about the index hole and starts to write at a random location. With a bit of luck you overwrite just a fraction of a sector written by the WD controller. Repeat until you succeed. The Apple writes the data with a different clock frequency than the WD controller. Thus every time you read the prepared disk with a WD controller, the WD controller's pll oscillator fails to synchronize with the bits of the manipulated sector on the floppy. Consequently the controller produces random information, plus a checksum error, every time you try to read the manipulated sector, very much like a hole punched into the floppy disk. From the outside the disks looks perfectly fine. And there is no way to duplicate that without a lot of effort, certainly not with a standard controller. This scheme still works today for PCs. The PCs floppy controller is just a clone of a NEC controller, which itself is a clone of the WD controller.

more than 8 years ago

Submissions

msbsod hasn't submitted any stories.

Journals

msbsod has no journal entries.

Slashdot Login

Need an Account?

Forgot your password?