Re: Apple //+ floppy technical info

[dalloff@freenet.columbus.oh.us (Dave Althoff)]

Nathan Mates (nathan@visi.com) wrote:
: In article <5aouuj$3kg@ren.cei.net>,  <kents@fs.cei.net> wrote:
: >Where can I find technical information on the Apple // disk format?  I need
: >info such as read/write gap length, format gap length, format interleave, etc.
: >Any help will be greatly appreciated.

:    The best reference is _Beneath Apple DOS_. Awesome reference,
: though in paperback form only. [Written in 81 when electronic
: publishing was a far-off dream] The Byte Works (email:
: mikew50@aol.com) might have a copy, though.

:    Reading up in there, standard DOS 3.3 tends to have (varies by disk
: speed) about 40 sync bytes between sectors, and a longer gap at the
: end of the track. 6 sync bytes after the sector's header.  As to
: interleaving, Pascal disks have +2 interleaving (0, 8, 1, 9,...),
: while DOS 3.3 appears to have -2 (or +14) interleaving (0, 7, E, 6, D,
: 5...) 4:1 interleaving ought to be fine, though I'm not sure on the
: optimal.

: Nathan Mates

According to either Beneath Apple DOS or the documentation for Bag of
Tricks (I forget which), DOS 3.3 uses -2 sector interleave, which is
optimized for a really quick boot cycle.  The trouble with that is that it
isn't particularly optimal for anything else.  A -9 interleave allows DOS
3.3 to access files significantly faster, but reduces the boot cycle to
glacial slowness.

With the Bag Of Tricks INIT program, there is a neat compromise available
that lets you have the best of both worlds.  The sector interleave is
physically encoded on the disk in the sector headers, so it is possible to
re-INIT tracks 3-35 on the disk with a -9 interleave, while leaving tracks
0-2 at -2.  This way, you get the quick boot, and the improved file access
times.

What I have noticed, though, is that the speed advantage of the -9
interleave seems to vanish if you use Pronto-DOS...so apart from some
tinkering a number of years ago, I haven't done much with this, since I
use Pronto-DOS wherever practical (except on my GS, of course, which is
running GS/OS).

--Dave Althoff, Jr.
-- 
    /-\      Celebrating the International Year of the Roller Coaster
   /XXX\      /X\     /X\_      _     /XX\_      _     _        _____  
  /XXXXX\    /XXX\  _/XXXX\_   /X\   /XXXXX\    /X\   /X\      /XXXXX
_/XXXXXXX\__/XXXXX\/XXXXXXXX\_/XXX\_/XXXXXXX\__/XXX\_/XXX\_/\_/XXXXXX