Some Information

7 March 2002

If some part of the disk is not MFM encoded, what is it? Well, there are a few things that can be on the disk:

• Sync values (not really MFM, just almost)
• Some sorts of protection

• Anything that is not decoded by the disk format

• Anything that can be reproduced properly using MFM encoding

We will probably not actually store Copylock density information in the release format disk image for various reasons. One particular reason is that we know how is it generated and we can recreate it perfectly every time. It would be easier to make this “data generator” for UAE (or other emulator), and the mastering software as they don’t have to know the cell sizes originally read for each bit, just how to recreate the proper cell size for each bit. Copylock density is always only one of two types, but some disks that have degraded over time no longer have a “perfect” Copylock graph. This means that these protections may fail their timing check but otherwise contain perfectly valid data. After processing these games will become fully authentic.

Note: We are not talking about the Copylock data here, as that is different on practically each game. We are talking about the varying density with which the data was written. For a visual example, see these density graphs.

This also helps the emulator. We can perfectly recreate the timings required for Copylock, so any timing glitches in emulation won’t affect the execution. So basically the emulator does not have to be cycle exact in order to pass the protection check - otherwise it would very probably need to be.