Date   : Tue, 24 Jul 1990 11:21:31 GMT
From   : uhccux!virtue!comp.vuw.ac.nz!munnari.oz.au!bunyip!iceman!zlraa@ames.arc.nasa.gov (Ross Alford)
Subject: Spell21

The question was:  what sort of disks to use in a DSQD drive for
820k.  The poster tried HD disks, and they didn't work.  Not
surprising:  HD disks have greater coercivity, meaning they are 
more resistant to magnetisation, and need stronger write flux.  This
allows more sectors/track without adjacent regions affecting one another
What you really want are DSQD disks, certified for quad density.  I
haven't seen these advertised for some time, but not to worry--I've thus
far used over 150 DSDD disks at 720k in a TEAC quad drive and have had
no failures, despite using a variety of no-name generic disks.  If you
are a worrier, run a verify program after formatting.  DSQD disks, when
they were available, were simply standard disks that had been tested
at quad density.

Ross Alford
zlraa@iceman.jcu.oz