GCR specification - where?

[ftww@cs.su.oz.au (Fred the Wonder Worm)]

I've recently unearthed my Apple ][+ and was somewhat surprised to find
that everything was in working order (I did clear the spiders out of the
case first, though).  Anyway, I want to find out precisely how the data
is laid out on the disk; much searching through FAQs and various other
places has revealed little more than that GCR (group code recording) is
used.

So now what I want is a description of how data is organized on the disk
under GCR, and how this is translated into bytes to move into memory.
Obviously I could look at RWTS, but it's likely I would misunderstand
something, and in any case the timing considerations would not be spelt
out.  So does anyone have such a specification handy?

Thanks for any help,
Geoff.

PS: While I'm here, I'd also like descriptions of what happens with the
    stepper motors in the drive.  I have a document by Neil Parker which
    mentions the four phases, but doesn't say what happens if more than
    one phase is on at once, or how long programs should wait before
    assuming the head is where they want it to be.

-------------------------------------------------------------------------------
Geoff Bailey (Fred the Wonder Worm)   |   Programmer by trade --
ftww@cs.su.oz.au                      |       Gameplayer by vocation.
-------------------------------------------------------------------------------