[RyanGuyardo (OP)]

Well some people say if you place a magnet near a memory card or a hdd, it will destroy it. Is this true?

[DoctorBeaver]

Yes, that is true. This is because the data is stored by directionally magnetising the disk in minute regions. One direction represents a 1, the other direction is 0. Bringing a magnet into close proximity with the disk can affect this directional magnetism and, thus, corrupt the data.

[syhprum]

Is it correct that a memory card will be damaged by a Magnet ?
I thought that the data was stored by trapped electrical charges.

http://searchstorage.techtarget.com/sDefinition/0,,sid5_gci212130,00.html?mboxSession=1236028852421-319417

[neilep]

Doctor Beave,

Does this mean that one could use a hard disk to record the signature of a magnet ? Would two identical magnets identically corrupt a disc with identical signatures ?

[DoctorBeaver]

syhprum - I'm not au fait with the workings of memory cards.

Neil  - I suppose in theory that would be true. Although I would imagine that making 2 magnets exactly identical would be nigh on impossible.

[lyner]

Doctor Beave,

Does this mean that one could use a hard disk to record the signature of a magnet ? Would two identical magnets identically corrupt a disc with identical signatures ?

Firstly, the field needed to magnetise a hard drive disc is very high and they are pretty impervious to external magnets. (It was only the early floppies that were really susceptible, I believe). The field from the 'write' heads is very high and very intense / localised - for the data density to be so high.
Secondly, the effect on a hard disc of a high enough field would be to put a great 'splodge' of 'magnetisation' onto it. The distance of the magnet would have as much effect as the strength so, different magnets and different arrangements would produce different 'splodges'. It would be a bit like holding a bit of photographic film up to a spotlight bulb - no detail would be visible. I don't think Inspector Plod would be able to spot which magnet dunnit.

Memory cards do not use magnetic recording. They are solid state and use 'flash memory'.

[techmind]

Ditto what the others said. Memory cards are effectively a silicon chip which stores tiny amounts of charge. Unaffected by magnets.

For hards discs you do need quite a high field so (while as a precaution you'd want to keep magnets well away) in practice you could probably bring a small "toy" magnet against the case with no ill effects. One other consideration is that a nearby magnet might affect/upset the motion of the head-armature inside the hard disk if it was operating at the time, so bringing a magnet too close is probably still a bad idea.

Several years ago I experimented with some floppy disks (not containing anything important) and found that I could wipe a pocket horseshoe magnet over the plastic case of the floppy without corrupting the data []. If I touched the magnet against the plastic disk inside then it was a different matter... []

[DoctorBeaver]

Many moons ago when I was a software development manager we used to send updates out on floppy disk. Some of these were arriving at their destination corrupted and we couldn't work out why. Then a sharp-eyed little secretary noticed that the companies who had received corrupt ones all had postcodes on our customer database and these had been written on the envelope along with the rest of the address. None of those without postcodes had been corrupted.

A phone call to a friend of mine who worked in the tech dept of the Post Office brought to light the fact that envelopes with postcodes went through a different machine that made use of magnets.