🚀 go-pugleaf

In article <4vvdb4$6...@lex.zippo.com>, h...@slc.unisys.com (Helge Moulding) wrote:

> Consider some of the other stories.
> 
> * the refrigerator magnet - most fridge magnets aren't strong enough for
>   two pieces of paper, never mind a floppy disk. And fridge magnets aren't
>   likely to damage the floppy, either, as weak as they are.

Yeah, that one bugs me, too. In fact, I heard it one too many times, and
finally prepared a demo for my user group. I brought in a loudspeaker with
a rather hefty magnet in it, and used it to "accidentally" pick up a 3.5"
floppy by the shutter. This speaker magnet was strong enough to hold both
the speaker (a fairly heavy one) AND a 3.5" floppy to the refrigerator.

After publicly bemoaning that I had "probably ruined" my demo by getting
all that "yucky magnetic stuff" all over my floppy, I suggested to the
crowd that maybe I could "wipe the magnetism off the floppy". I then
proceeded to rub the floppy vigorously all over the magnet - both sides,
and all four edges. I even opened the shutter, and tapped the floppy
against the magnet "to shake loose any magnetism that had gotten inside."

Then I left the speaker hanging from a convenient metal surface while I
put the floppy in the drive, ran a few programs from it, copied the whole
thing to the hard drive (I had about 1.3MB of data on a 1.4MB floppy),
including a program that could do a checksum on the disk. When I ran the
program, it produced the same checksum as it had when I made the floppy a
week before. 

During most of that week, I had left the floppy sitting under my
telephone, one of those classic jobs that actually uses electromagnets to
ring the bell. That didn't hurt it either.

The risk to floppies from magnets and ringing telephones is, as they say,
greatly exaggerated. I advise the doubters to try the experiment for
themselves.

A couple of caveats (since I'm sure someone else will mention them if I don't):

 - A 3.5" floppy has a plastic case the provides a little physical
   separation between the recording surface and an external magnet.
   This does make a difference. When I tried the same experiment with
   a 5.25" disk, the magnet did indeed produce bad sectors.

 - If I put the 5.25" floppy inside one of those cardboard mailers, one
   with cardboard a little thinner than is normally found in shoeboxes,
   the magnet would still damage it. But if I put the floppy on one side
   of the mailer, and the magnet on the other (so that I had two thickness
   of the cardboard between them), then the magnet did not harm the floppy.

 - Curiously, this applied even if I stuck the floppy to the refrigerator.
   That is, a four-layer sandwich consiisting of

      "magnet":"mailer (both layers)":"5.25 floppy":"refrigerator"

   caused no harm to the floppy, even though the the magnet was strong
   enough to hold the whole ensemble in place. Keep in mind that the magnet
   still has a speaker attached to it, and is holding that up as well.

   I say curiously, because the lines of magnetic flux should be nearly 
   parallel in this configuration, so the strength of the field should
   be nearly constant with distance. I'm just reporting the results of
   the experiment. I'll let someone else explain it.

 - I also have a bulk eraser, a legacy of my youth in the days before it
   was feasible for an ordinary person to own a computer, and I was into
   audio technology instead. This bulk eraser was designed to erase an 
   entire reel of magnetic tape at once. It can erase a floppy, even the 
   3.5" variety, just dandy, even from about 1/4" away. (It can also 
   distort the image on my monitor from about 4 feet away. No one is
   going to leave such a strong magnet anywhere near their monitor.)

-Ron Hunsinger