🚀 go-pugleaf

This is a confusing subject.  I take it that trying to format the 3.5"
disk produces "Bad or Invalid Media" (sic) and trying the 5.25" gives
"Track 0 Bad, Disk Unusable" Put a piece of opaque tape over the notch
opposite the write-protect notch and a HD 3.5" diskette is DD is
wearing the clothes of DD and will format, read, and write DD.  The
only cure for the 5.25" disk is a kludge: put a 360K disk in the
drive, issue FORMAT, after DOS reads the boot record it says "...Press
RETURN to start" (or something) pull out the 360K and put in the 1.2
Mb disk.

The problem is this.  The 5.25" floppies double their capacity by
doubling the number of tracks.  Hence the wide read head of the lower
density drive can't read a single track, and it can't read the disk's
boot record.

The 3.5" floppies double their capacity by doubling the number of
sectors in a track.  Hence the track density is the same for DD and
HD, and the lower density drive will read the boot record without
problem.  Oh, no!  People can format HD disks in DD drives!  We'll put
a hole through the diskette case, so the machine will know there is a
floppy with a thin coating in the drive and will refuse to cooperate
with such unorthodox behavior.

This concern with improper use was explained nicely by the last
respondant (but which I'll expand on anyway). HD diskettes are coated,
like DD, but then polished more to reduce surface bumps that would
produce magnetic irregularities.  This thins the coating.  The lower
density drive is designed to penetrate a thick coating with magnetism;
when it does this to the thin coating, the magntic domains grow
sideways rather than downward and may interfere with other tracks.

Mother Industry protects us from such folly (though it may work).

Bruce (Gypsy Scholar)
-- 
Department of Geological and Geophysical Sciences
Princeton University, Princeton, NJ 08544
bathurst@phoenix.princeton.edu bathurst@pucc.bitnet !princeton!phoenix!bathurst