"intelligent" disk drives

[Chuck Guzis]

On 18 Nov 2007 at 16:41, Roy J. Tellason wrote:

> > 'course, if they HAD gotten 500MB/side (v 400-500KB), then it would have
> > been well worth it.
> 
> Speaking of which,  I recall seeing announcements every so often of floppy 
> drives that would have seriously more capacity than the usual stuff.  
> Something about "vertical format" sticks in my mind,  though not much more 
> than that.  Is this what that LS120 was all about?  I think I ever only 
> encountered _one_ of those drives...

Maybe you mean perpendicular recording (PMR) that was used in the 
2.88MB 3.5" floppies.  Very unreliable.   DSHD 3.5" diskettes are 
rated somewhere around 17-18 kbpi density; an LS-120 exhibits about 
45 kbpi--the real capacity gain is achieved by packing more tracks on 
the disk.  The LS-120 does this with an overlay that guides as IR 
laser servo setup to get 1376 tracks per side.  The disk is spun 
faster to improve S/N.

The Zip drives use an "embedded" servo for positioning; that is, the 
servo information is part of the normal track.  In addition, Zip 
disks have extra tracks called "Z tracks" which, among other things, 
track and hide bad sectors so that every disk looks more-or-less 100% 
"good".  You cannot low-level format a Zip disk--if you degauss one, 
it's trash, since the servo information is written at the factory and 
nowhere else.

The Iomega drives were not the first floppies to use embedded servo--
Drivetek was--and obtained about 2.8MB and later 6.4MB on a 5.25" 
diskette.  If you happen to run across one of the 2.88MB ones, try 
reading it in a 1.2MB drive--you'll find that you can see every other 
track; thus, the Drivetek recorded 160 tracks per side.  It used a 
dual-positioner technology; a "coarse" positioner and a "fine" 
positioner.  But like all embedded-servo drives, the media was 
factory-formatted.  (BTW, Wikipedia is utterly silent on Drivetek).

Hope this helps.

Cheers,
Chuck