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From: Ralph Mowery on 4 Apr 2010 07:44

"davy" <davy.48w5sk(a)no.email.invalid> wrote in message
news:davy.48w5sk(a)no.email.invalid...
>
> Keep it away from hard drives...!
>

Have you ever taken a hard drive apart and looked at the magnet in it ?


From: Barry Watzman on 4 Apr 2010 08:10
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.


davy wrote:
> Keep it away from hard drives...!
>
> davy
>
>
From: BillW50 on 4 Apr 2010 09:49
In news:hp9vkb$m6d$1(a)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.

--
Bill
Gateway MX6124 ('06 era) 1 of 3 - Windows XP SP2


From: Barry Watzman on 4 Apr 2010 13:40
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(a)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.
>
From: BillW50 on 4 Apr 2010 15:43
In news:hpaiu5$kc0$1(a)news.eternal-september.org,
Barry Watzman typed on Sun, 04 Apr 2010 13:40:17 -0400:
> 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.

I would normally agree and I won't think that a degaussing coil found in
a color monitor could erase a disk. But one tech showed me otherwise. As
he had a monitor that would have about 1 in 5 chance to erase a floppy
that was placed on top of the monitor. Since these coils are generally
controlled by a simple PTC thermistor, there isn't much to go wrong. So
either by design or malfunction, this one could erase a floppy. So if
there was one in the world, surely there must be at least a handful of
others out there that could do the same.

> 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).

I never played with those and some have reported those bulk erasers
doesn't do a very good job of erasing either. As I hear much of the
information is still there anyway.

> 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.

They could be strong magnets, I don't know. As I never tested one.

--
Bill
Gateway MX6124 ('06 era) 1 of 3 - Windows XP SP2


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