A normal degaussing coil won't erase a disk, and the ones inside the set
are particularly weak. People who service color CRT devices sometimes
have much stronger coils that MIGHT be able to erase a floppy disk.
One thing that some people have that could erase a floppy (but not a
hard drive, generally) is a bulk tape eraser made for videotape (e.g.
VHS cassettes, or, if anyone has one, 1" or 2" broadcast open reel video
tape). These are rare, however, and you have to get it right up against
the disk (which is why even those probably won't work on a hard drive).
As someone pointed out, some of the strongest magnets you can easily get
are magnets removed from the voice coil mechanisms (the head positioner)
of .... HARD DRIVES. Those are seriously strong magnets, they are
mounted INSIDE the drive itself only about 1/2" from the platters ....
and they do not erase the platters, obviously.
BillW50 wrote:
> In news:hp9vkb$m6d$1@news.eternal-september.org,
> Barry Watzman typed on Sun, 04 Apr 2010 08:10:47 -0400:
>> More myth than reality. While hard (and floppy) drives are magnetic,
>> it is just about IMPOSSIBLE, with any magnetic source that normal
>> people have access to, to erase a hard drive or floppy from any
>> significant distance. The read/write head is extremely close to the
>> platters (microns, for a hard drive, and touching for a floppy).
>> Strenght decreases by the square of the distance. By the time time
>> you are even just 1/4 to 1/2 inch away, erasing the disk is almost
>> impossible. By the time you are 2 inches away, "almost impossible"
>> becomes "essentially impossible", unless you have access to something
>> like an MRI machine.
>
> Others and I have done a lot of research into this area. And there are
> lots of myths and legends here. First all, it is a myth that a weak
> magnetic field will corrupt magnetic data in time. It just doesn't
> happen. While it is true that magnetic data doesn't store forever, but
> it isn't do to other weaker magnetic fields. Although the problem of
> print through, is still a bit of a mystery to me. Which happens with
> very thin magnetic tapes.
>
> Thus to write or destroy magnetic data, you need a very strong and very
> close magnetic field to do so. And there is a trip point. As a field
> just a tad too weak won't do anything. And one just barely strong enough
> will. The drive heads doesn't produce a strong enough field to say pick
> up nails or anything. But it is highly focused to a very small point.
> Thus why it works.
>
> And it is true magnetic fields you are likely to run into during normal
> day to day life isn't strong enough to do any harm. I also know that
> refrigerator magnets are not strong enough to harm anything. I am not
> sure if a 5 lbs magnetic is strong enough to do anything either.
>
> Now there is one device that some might have around (more so in years
> past) that could wipe out a floppy disk. Not sure about a hard drive.
> And that is a color CRT (TV and/or monitor). As there is a large coil
> around the CRT known as a degaussing coil. And they are usually designed
> to kick in briefly whenever you power up the device. And some of these
> coils in some of those devices are very close to the top. And some rare
> color monitors for example have been known to wipe out any floppy disk
> sitting on top when you power them up. Fortunately most color monitors
> won't no matter how much you try.
>
> There are manual degaussing coils too. I have one made for degaussing
> tape deck heads. And I could never erase a floppy with it. And it barely
> works for degaussing CRTs manually. So the one I have isn't quite strong
> enough to harm any magnetic data either.
>