[Coco] 3.5 in 720K vs 1.4 meg floppy diskettes

[Marty Goodman]

It's true that the 1.4 meg 3.5 in floppies have a different (higher)
magnetic coercivity than the 720K variety.

HOWEVER, the difference between a 3.5 in 720K and a 3.5 in 1.4 meg is not
all that great... about 16% different, or something like that (I vaguely
seem to recall the 720's had a coercivity of 600 oersteds, and the 1.4's had
a coercivity of 700 oersteds.  This really isn't that big a difference, and
it would not surprise me to learn the 1.4 megs will work acceptably in the
720K drives (or in a 1.4 meg drive set to act as a 720K drive).  Acceptably
well, perhaps... but it's not clear the reliablity will be the same, nor
that the amount of time the data will last on them, when used as low density
diskettes, will be the same, either.

With 5.25 in floppy diskettes (remember them?) it's another matter:  The
360K "low density" 5.25 in floppies had a magnetic coercivity of 300
oersteds, if I recall correctly, and the 1.2 meg "high density" 5.25
floppies had a magnetic coercivity of either 600 or 700 oersteds (I think it
was 600).  THAT is an enormous different, and it thus surprise no one that
the 1.2 meg "high density" floppies CANNOT be written on a CoCo style 360K
floppy drive.

 ---marty