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I've always been told never to let magnets near computers. This seems mostly because of the hard drive and because of the screen, if it's a CRT. However, hard drives contain extremely strong magnets (for moving the heads), only a couple of centimeters from the spinning disk, and some laptops (Macs, at least) use supermagnets for various structural things (lid, power cable). I'm starting to think that this caution may be more myth than fact, but I don't want to sacrifice anything valuable finding out. So, two questions arise:

1. How vulnerable are hard drives to magnets? How about flash SSDs?

2. Are other pieces of the computer especially affected by magnets? Could a strong moving magnet induce a harmful current in a computer from outside, say, the case of a laptop?

Strangely after I put a tv aerial on top of a notebook (it has a magnetic base) above where the hard drive goes, it would not load part of windows properly on reboot, though it was running and shut down fine.

Typically the voltages induced by magnets moved by hand are rather low. In order to induce a voltage that is sufficiently high, one either needs to move the magnet very fast (think of a drilling machine for example), or use some coil with a high number of turns. I would thus not expect any damage from induced voltages.

The same applies to any kind of flash memory - SSD, USB sticks, flash cards... These store information in the form of some charge that is trapped between insulators, and this charge will not get lost unless it is overwritten. But writing a flash drive again needs a sufficiently high voltage, higher that what one would expect from a simple magnet.

In contrast, magnetic storage media such as floppies or hard drives are rather sensitive to magnetic fields. The bits on such media are quite stable in a weak magnetic field such as the natural field of the earth, but as soon as a critical field strength is reached, they swap and follow the direction of this external field. This is well below the field strength of a typical household magnet, so you can easily erase a floppy with such a magnet. (Although it is not a safe way - there remains a small magnetization of the floppy, which is way to weak to read it in a floppy drive, but can be used to restore the data using data forensics.)

In general I would be careful with strong magnets and computers - not because of induced voltages, but rather because magnetic parts could be attracted, or iron parts could be magnetized and then affect things like floppies or hard disks. A CRT could also be magnetized and then show a distorted picture. Weak magnetic fields caused by things like a Mac power plug should be no problem, as long as you keep them away from floppies.

Actually, the idea of restoring the previous state is mostly mythical, too. It goes back to long-obsolete hard-disk technology (RLL) and has to do with imperfect alignment and the tolerances involved. Bulk erasers (a very powerful magnetic field, essentially) are quite successful at wiping floppy diskettes and likely with hard-disks, too, though I'm not inclined to bother with an empirical test, myself.

To have a play for yourself, there are several readily, freely, available 'software forensics' suites and it's actually quite an interesting even lucrative, field.

Isn't BIOS ROM stored in a type of flash memory? Could you erase it?

Of course, in most cases. There is a thread somewhere around here discussing 'BIOS viruses' precisely because of that. Furthermore, has it never occurred to you that BIOS updates are simply rewriting the EPROM (which is what was normally used)? ;¬)

Some very old machines and possibly some current 'high security' machines used a ROM, as in, no ability to erase or modify at all. In these cases, no, you could not. ICs are unaffected by magnets, by and large, though, so wiping BIOS is not worry when messing with your magnets.

And in any case, take a look at the big fat magnet on the backend of your pc speaker sometime. What everyone is saying is correct -- the "no magnets" thing is basically a myth, except for placing strong magnets directly on your magnetic media.

So would a laptop with an SSD be effectively invulnerable to small (super)magnets at low velocities then?

Low power magnets (..fridge magnets/etc) == safe.
Rare-earth magnets == dangerous, keep away.
Powerful Electromagnet fields == KEEP AWAY FROM MY PORN COLLECTION YOU MAGNET WIELDING WIZARD!

NickJohnson wrote:So would a laptop with an SSD be effectively invulnerable to small (super)magnets at low velocities then?

Neither NAND or NOR flash would be effected, as they do not use magnetic miens of storage. http://en.wikipedia.org/wiki/Flash_memo ... _operation

If you wish to test, take a cheap pen drive, put some music on it, open it up, and try it. Nothing will happen.


However, some people think Because they do not use magnetic storage SSD's will last forever, Unfortainetly the are wrong! Horribly wrong! [/chowder]

A few years from now I expect all computers to not be effected by Magnets

Coddy wrote:However, some people think Because they do not use magnetic storage SSD's will last forever, Unfortainetly the are wrong! Horribly wrong! [/chowder]

Er? You link to a Wikpedia page describing that the memory has a finite amount of erase cycles. That has nothing to do with "lasting forever". Also, low-density magnetic storage can last for quite a while. My mid-80s 360KB floppies are still readable.


JAL

@jal: Sorry, I was basically meaning that, I have seen many people think that because It is solid state, they can just format it, and put/erase files on/off of it heavily, and it will never damage the memory in the long run. I was just pointing out that they have there flaws aswell.

jal wrote:Also, low-density magnetic storage can last for quite a while. My mid-80s 360KB floppies are still readable.

I'm aware of this, as long as there kept in a good location anything will last a good long time, infact my dads Atari 800xls floppies still have easys on them.

Wtf are "easys"?

EDIT: Oh...

TylerAnon wrote:Wtf are "easys"?

A misspelling of "essays", from context.

What's funnier is that I read it as essays, never even saw the typing error until now. Reminds me of that oft-quoted study about word shape. :¬)