Re: GCR specification - where?

[russotto@wanda.vf.pond.com (Matthew T. Russotto)]

In article <330430CF.23DE@siemens.at>,
Dr. Wolfgang Otrebski <wolfgang.otrebski@siemens.at> wrote:
}Matthew T. Russotto wrote:
}<snip> 
} 
}> Sure they are.  Just count cycles :-).  Though somewhere in the dusty
}> attic of my head I remember that it takes 32 cycles to write a disk
}> nibble and 40 seconds to write a self-sync nibble.  So first you write
}> a few self-syncs, then every 32 cycles you need to load the data latch
}> with a new value until you're done writing nibbles.  Then I think you
}> write some more self-syncs, but I'm not sure.  In any case, it's all
}> in the book.
}seconds above read cycles ... 40 seconds would be awfully long :-)

Oops.. hey, I got it right two out of three times.  What's a factor of
a million here or there?

I think that 13-sector disks may have had a 9-bit self-sync nybble
because the P6 prom couldn't accept two zeros in a row.  I think that
means more self-sync nybbles had to be written, but I'm not sure.

I've seen one copy protection scheme which apparently used no
self-sync nybbles at all, or at least very few.  Instead, it just kept
retrying until it got in sync.  As you may have guessed, it was
ungodly slow.  Very resistant to copying, but I beat it anyhow -- it
had a normal DOS otherwise, so I just loaded the programs, saved them
onto tape, and re-loaded them onto a normal DOS.  Funny thing is that
this program was for a speech recognizer -- why copy protection when you needed
special hardware anyway?
-- 
Matthew T. Russotto                                russotto@pond.com
"Extremism in defense of liberty is no vice, and moderation in pursuit
of justice is no virtue."