OnlyMortal|10mon ago

I used to crack C64 disk games. They were mostly trivial because I wrote a disk sector editor that would disassemble blocks on demand.

One that comes to mind were Ocean’s copy protection that was hacked by a load of 1 into the accumulator and a return. They had a “bool IsValidDisk()” type of routine.

After cracking one of their games I could crack others in less than 2 minutes directly on a copied floppy.

skissane|10mon ago

Random (yet on-topic) question: does anyone know of any IBM PC(-compatible) games/apps which used deleted floppy sectors as part of their copy protection scheme? I can find examples for 8-bit platforms such as Atari, BBC Micro, Amstrad CPC - but not IBM PC, even though the original IBM PC floppy controller supported them.

For those who don’t know, deleted sectors are an obscure legacy feature which was part of IBM’s standard for floppies, and floppy disk controllers which aimed at IBM compatibility often supported it. Essentially, the floppy can contain two types of sectors, normal and “deleted”, with a flag byte in the sector header distinguishing the two, special commands to read/write the deleted sectors, and a setting on the controller to determine whether the normal read sector command skips deleted sectors or not. Very little software used it; copy protection was the main exception. The original use case was to support very primitive databases in which each database record was stored in a separate sector, and hence you could delete a record in-place by marking the sector as deleted.

Platforms which used off-the-shelf IBM-compatible floppy controllers generally supported them, e.g. IBM PC and compatibles, Ataris, Acorns, Amstrad CPC. Whereas platforms which rolled their own floppy controllers, such as Apple II, Macs, C64, generally didn’t.