This is in response to suggestions I've heard on how to
format 720K diskettes to 1.44 megabytes.  I've seen various
articles on how to modify disk drives to allow this and I have
seen ads for a device that punches holes in the diskette case to
fool the drive sensor.  All these tricks are a bad idea.  You
risk losing your data if you format a 720K diskette to 1.44
megabytes.

     The reason is the nature of the diskette media.  Data is
written with a stronger magnetic field on the 1.44 meg diskettes. 
Using such a strong field on a 720K diskette makes the bits on
the disk too strong for the medium, and they will gradually
migrate out of position as they are attracted to and repelled
from each other by their magnetic fields.

     The 720K diskette is designed to be formatted and written to
with a magnetic field strength of 300 oersteds.  The 1.44 meg
diskettes are high coercivity media; they require a magnetic
field strength of 600 oersteds, twice that of the lower density
diskettes.  The high capacity diskettes are less sensitive to
magnetic recording (that's why they require a stronger magnetic
field).  This allows the bits to be recorded at twice the
density, or twice as close together.  Because the medium is less
sensitive, the bits will not interfere with each other.  On a
more sensitive medium, such as that used for 720K diskettes, the
bits must be farther apart to eliminate interference with each
other.  That's why you cannot get as much information on the
disk.

     The book Upgrading and Repairing PCs, by Scott Mueller
(Carmel, Indiana: Que Corporation, 1988), contains this warning:

     "You should not actually store any important data on
     this incorrectly formatted disk because the data is
     recorded at twice the recommended strength and density. 
     Over time, the adjacent magnetic domains on the disk
     begin to affect each other, causing migration of the
     domains due to the magnetic attraction and repulsion
     effects ....  Over time, the disk seems to erase
     itself.  The process may take a day, a week, a month or
     more, but the result is pretty much inevitable." (page
     316)


     He goes on to say that incorrectly formatting the disk also
ruins the disk because you cannot then reformat it to a lower
density.  When formatting to a lower density the drive writes
with a weaker current, which cannot overwrite the high-volume
information now on the disk.  The only solution is to use a bulk
eraser.

     So ... Don't do it.  The disk will seem to format correctly,
but you'll be sorry later when your data fades into the magnetic
sunset!