Are Flash Cards Vulnerable To Magnetic Fields?

[Crushdepth]

The reason I ask is that I stupidly left a couple of small but very strong magnets sitting on my desk. I must have put my compact flash card/reader down on top of them, because I found them stuck to the bottom of the flash card when I picked it up (does that sound like a horror story or what).

The data on the card *seems* ok - there's a lot of stuff on it, and so far I haven't found any damaged files, just curious as to why it didn't mangle the whole card...

[Tywais]

Flash cards are solid state devices (similar to the RAM in your computer but non-volatile - that is, maintains the data with no power) and do not use magnetic fields to store the data like hard disks or floppies.

Edited May 27, 2006 by tywais

[paulfr]

Flash devices are indeed solid state semiconductors. Specifically, they are made with something called a floating gate field effect transistor as the storage element. A conducting region is isolated from the gate and when programmed, it has charge injected across the dielectric to the floating island. This charge stays there permenantly and can later be detected (or read).

The reason the magnetic field did not destroy any data is that it works on primarily electrostatic principles rather than magnetic.

However I think there may be some limit to this for exceptionally large magnetic fields (especially if they are changing with time) that one finds in physics labs and particle beam accelerators. I do not know what it is, but it would be much larger than anything you could find at home or work.

Edited May 27, 2006 by paulfr

[tjo o tjim]

Other obvious exception is if your CF card is a microdrive (hard drive-based).

[Tywais]

However I think there may be some limit to this for exceptionally large magnetic fields (especially if they are changing with time) that one finds in physics labs and particle beam accelerators. I do not know what it is, but it would be much larger than anything you could find at home or work.

You know me paul, running a medium energy accelerator. We have a magnet that bends a 2.5MeV electron beam about 380 degrees (alpha shape) plus one that bends a 20MeV beam 60 degrees. Might be interesting to take one of my old retired flash drives and put it into the field (about 1 Tesla) and see what happens.

Since they are charge storage devices it might migrate the charge to somewhere else.

[elkangorito]

I would suggest that all electrical/electronic devices are in some way, affected by magnetic fields. Some devices are affected easily whilst others are not.

There are 2 theories to the existence of magnetism;

1.

The uniform alignment of the crystaline structure of some metals.

2.

Electron spin at atomic level.

You may have found a different result with your flash card had it been very close to a large AC (alternating current) electromagnet, which is a similar device used to de-gauss large sound recording tapes clean in seconds (degauss means to de-magnetise).

Small magnets with an unchanging magnetic field should not be a problem unless you go waving these magnets around your flash card.

Edited May 27, 2006 by elkangorito

[Tywais]

The reason I ask is that I stupidly left a couple of small but very strong magnets sitting on my desk. I must have put my compact flash card/reader down on top of them, because I found them stuck to the bottom of the flash card when I picked it up (does that sound like a horror story or what).

One other thing since you have magnets sitting on your desk, don't put your credit or ATM cards on them or you might get a nasty surprise the next time you try to use it.

[astral]

There are other computer components like screens and disks that can be damaged.

Get those magnets off the desk and tucked away out of reach.

[Firefoxx]

Actually, typical magnets that you can buy don't affect the magnetic strips on credit cards and the like. This was shown to be a myth on the Mythbusters show. You need an *extremely* powerful magnet to affect the information stored on those cards.

[elkangorito]

Actually, typical magnets that you can buy don't affect the magnetic strips on credit cards and the like. This was shown to be a myth on the Mythbusters show. You need an *extremely* powerful magnet to affect the information stored on those cards.

How did 'Mythbusters' use the magnets to bust this purported myth? What is a 'typical' magnet?

Edited May 28, 2006 by elkangorito

[Tywais]

Actually, typical magnets that you can buy don't affect the magnetic strips on credit cards and the like. This was shown to be a myth on the Mythbusters show. You need an *extremely* powerful magnet to affect the information stored on those cards.

couple of small but very strong magnets sitting on my desk

Are you willing to chance it there Firefoxx?

"No matter how much they tried or how long they left the cards in the wallet, they could not erase it. In fact, it took over 1,000 gauss to erase a credit card - a gauss measurement that high could not be found in any household magnets, money clips, or wallets."

Samarium Cobalt or Neodymium magnet field strength ~8000 gauss. I used to play around with some of these and they are deceptively powerfull. Easy enough to buy but probably not what the OP has though he does say very strong magnets.

Also you don't have to erase the entire strip, just a few bytes in the wrong place (enough to screw up the CRC checks) and it will be useless.

Edited May 28, 2006 by tywais

[Firefoxx]

The thing about these very small but extremely powerful magnets you're talking about (rare earth type) is that they *do* have a monstrously large magnetic field. However, the field's size is tiny. Very very tiny. Not only that, you'd actually need to be rubbing the two (CC and magnet) together to get any effect.

I stand by my statement, but of course I'm not saying that you should go out, buy a super-magnet, and put it in your wallet just for fun. For gorito, you can catch the show on UBC reruns (or download it). As I recall, they used an electromagnet.

[Tywais]

Actually, there are two types of magnetic cards.

One is referred to as Hi-co (short for high coersive) meaning they require a high coersive magnetic force to write to them used mainly in credit cards. the other is Lo-co or low coersive cards used mainly in hotel room keycards and cards that are re-written often. the Hi-co cards are nearly impossible to erase with an everyday magnet. A Lo-co card however is easily erasably with any sort of relatively weak magnetic field.

Yes, the issue may be mute but why take a chance not knowing the quality of the cards and just keep the magnets out of the way.