Re: High and Double density floppies

[valthoff@magnus.acs.ohio-state.edu (Victoria M Althoff)]

Sorry...by 'substrate' I was referring to the plastic disc itself, which the 
medium (oxide particles) is actually attached to.

Looking at this entire thread (and knowing that INIT assumes that the disk is 
unformatted and completely blank...unlike some ProDOS formatters), and what 
little I know of recording technology, it looks to me like the problem is with 
the type of oxide used on the HD floppy.  The size of oxide grains shouldn't 
matter, since the (comparatively) large Disk ][ read/write head will just move 
more particles.  But if the type of particle requires a higher magnetic flux be
present (provided by a smaller head gap and a higher power level in the head) 
to record the signal, that could prevent proper writing.  At first (as in my 
previous post), I thought this didn't make sense.  Then I remembered that 
little tidbit from working in radio:  you cannot use a common audio-tape 
bulk-eraser to bulk-erase an R-DAT digital audio cassette, because the 
metal-particle tape requires a much stronger magnetic field to rearrange the 
particles.  Apparently, this is the same thing that is happening with the HD 
disks.  Most enlightening.  This probably also means that while a 400k or 800k 
(or, presumably, a 720k) drive can successfully format a 1.44Mb floppy, those 
smaller drives might not be able to write to a 2.88Mb floppy.

EXPERIMENT TO TRY just for the heck of it:
Fill a 1.2Mb diskette with 'meaningful garbage', then attempt to INIT it on a 
Disk ][ or UniDisk.  Then, return to the 1.2Mb format machine, and see how much
of the data remains intact.  If all, or virtually all, remains intact, then the
difficulty is probably just as I mentioned above.  Otherwise, I'm just as 
baffled as everyone else.

--Dave Althoff, Jr.
(Hey!  When I'm wrong...)