🚀 go-pugleaf

in article <7436@xanth.cs.odu.edu>, scott@flounder.cs.odu.edu (Scott Yelich) says:
> My drive formatted and used 11/82.  Once and a while when doing a lot
> of reads-- the drive would make a clanking noise...  That's when I decided
> that 82 was too much..  I still used 11/81.
	About 30% of the 3.5" drives Atari has sold will work with more
than 80 tracks.  (This is based on info gathered when I was at Data
Pacific.)  If you have a drive that supports more than 80 tracks it
works just fine.  But if you ever need to read that disk on a drive that
only supports 80 tracks you will be SOL.

> I have since found the name of that track offset-- TWISTED.  I think what
> it is supposed to do is scramble the formated sectors on the tracks to
> allow the required access-time to decrease.
	TWISTER (written by Dave Small and myself, published by STart)
skews the sectors on the disk so that sector 1 is not always located by
the index hole.  Sector one is moved by 2 sectors for each track.  (eg.
track 0 has sector 1-10 in sequence, track 1 has sectors 9-10 followed
by sectors 1-8.)  The skew allows time for the head to step (3 milli-
seconds) and for it to stop vibrating (about 30 milli-seconds) before
sector 1 arrives.  This allows the ST to read every track on the disk in
just over 80 revolutions of the disk (single sided), a normally
formatted disk takes 160+ revolutions of the disk to be read.
	TWISTER also formats the disk with 10 sectors per track instead
of the standard 9 sectors per track.  On a drive spinning anywhere near
the correct speed (300 RPM) this is not a problem.
	The newer ROMs from Atari (Mega ROMs and the unreleased 1.4
ROMs) also skew the sectors on the disk, though they only shift one
sector per track.  That works as long as very little time is required
for the head to stop vibrating after the step.

> But, I don't see how this can be considered dangerous!  All you are doing
> is changing the sequential order of the formated sectors!  (The old
> 8bit atari did this just fine)
	The only "danger" with non-standard formats is lack of
portability between different STs.  Most STs can not handle disks
formatted with 11 sectors per track since their drives are spinning at
the correct speed.  Only drives that are spinning slower than normal
have the time to put 11 sectors on a track.  Also most STs can't handle
disks formatted with 81 or 82 sectors per track since the drives have a
physical stop at the 80th track.
	If you are not worried about using disks on other STs then use
11 sectors per track with 81 or 82 tracks.  If you want all other STs to
be able to use your disks stick to 9 or 10 sectors and 80 tracks.



				Dan Moore
				AT&T Bell Labs
				Denver
				dlm@druhi.ATT.COM
				dlm@druwy.ATT.COM