Apple II disk format

[MattCarp]

Does anyone have a good primer on the Disk II data encoding scheme, Group Code Recording (GCR)?

I'm looking to archive my various Apple II floppies. I know PC disk controllers can't read them, but I have a Catweasel "universal" floppy controller. I hope to modify some of the software that comes with the card to read the Apple diskettes and need to understand the technical details around the actual physical disk format.

-Matt

 

[david__schmidt]

You want to find a real or online copy of Beneath Apple DOS and/or Beneath Apple ProDOS. Here is a citation of some relevant bits for you:
http://www.umich.edu/~archive/apple2/misc/hardware/disk.encoding.txt