Apple II GCR

The Apple II provides very fine-grained control of the drive from software, so various kinds of schemes were devised.

A discussion of how the Disk II works: http://www.metafilter.com/114962/jmp-TRIGSPIKES#4301468

There are two "standard" Apple II GCR formats, 13-sector and 16-sector. Both are explained in detail in Beneath Apple DOS.

http://www.classiccmp.org/cini/pdf/Apple/Beneath%20Apple%20DOS.pdf

Prince of Persia and other software used a format called RWTS18, designed by Roland Gustafsson to pack the maximum possible data onto a disk. Some details can be seen here:

http://pastie.org/private/mivibuirv3nomrqndjblcw

Not everything in that old cracking guide is accurate. For example, normal-speed drives were used to write RWTS18 disks.

RWTS18 disks interleave the GCR 6+2 data to make it possible to stream the bytes, without having to use a buffer to decode. Apparently Tangled Tales used the same format (probably stolen RWTS18 routines, though possibly licensed). See the Tangled Tales guide at http://www.textfiles.com/apple/CRACKING/tangled.txt for details.

More will be added soon.