laptops and magnets and damage

August 3, 2006 3:59 AM

Can a laptop hard drive be damaged by small magnets? (more inside)

Disclaimer: I'm no techie, so I have no idea about the possibility of whether this could happen.

A work colleague has an older laptop and has been trying to get our boss to OK buying a new one with all the usual bells and whistles, but the boss has always maintained that what is being used is OK for work. This week he came in and said that the laptop had stopped working after he sat it on a new laptop bag he recently bought (using the bag as a cushion under it). The bag had a flap on it secured by two small magnets to keep it closed and he claims that the magnets damaged his hard drive and it is now unusable. Our IT department says the drive will neither spin up, nor can it be read and so is basically just a paperweight.

So my question is could the magnets in the flap of a bag actually really damage the hard drive to that extent or has he (as we suspect) sabotaged it somehow to scam the boss man and get the new widescreen Dell he covets?

posted by 543DoublePlay to computers & internet (17 comments total)

Well, the instructions tell me to keep my external USB HD away from magnets, so I guess so. Of course, he could still have sabotaged it with magnets.
posted by A189Nut at 4:01 AM on August 3, 2006

It's possible for magnets to wipe a drive (though it's more difficult than most people realize), but I've never heard of them making it so that a drive won't even spin up.
posted by Steven C. Den Beste at 4:02 AM on August 3, 2006

In my experience no. I have at times been tasked with bulk wiping hard drives slated for disposal. A large magnet couldn't do it, so I doubt a magnetic clasp could either. Not enough Gauss
posted by Gungho at 4:02 AM on August 3, 2006

No way. Not a small magnet like that.

The magnets in the drive that used to read and write the disk are very powerful and made from rare earth elements like niobium. They are always within a centimeter of the media and their fields don't damage the disk in any way.
posted by joegester at 4:06 AM on August 3, 2006

Gotcha then. Your boss could always just buy a new hard drive for the old laptop...
posted by A189Nut at 4:25 AM on August 3, 2006

What Joegester says is correct, once you've played with and got a feel for the power of those magnets, you'll never be worried about small magnets near your computer again.
posted by tomble at 6:37 AM on August 3, 2006

And the survey says: Scam! A sneaky but nice idea A189Nut, but I have to think of office politics.
posted by 543DoublePlay at 7:30 AM on August 3, 2006

Cases with magnetic closures are actually fairly common for electronic devices such as iPods and notebook computers. This has always struck me as a little odd, but joegester's point got me thinking.

I'm no expert on hard drives and with luck an expert will pop up and correct any errors I make here, but the drive head itself actually has to be a hell of a lot closer to the platter than a centimeter (I believe it's on the order of nanometers) for reading and writing, but this uses an electromagnetic coil to write and a magnetoresistive material (or in the old days, an inductor) to read. The head doesn't use any kind of permanent magnet. The magnetic phenomena it uses are taking place on the nanometer scale but the individual bits are closer to micrometer size, so adjacent bits should not be affected. If any powerful magnets are present in the hard drives as joegester suggests then they are presumably in the motors that spin the drives and move the heads.

You could certainly render a drive unreadable with a powerful magnet but I would think to break a drive so that it won't spin up you'd have to use the sort of electromagnet they use to move cars around at the junkyard. Perhaps your co-worker treated his drive to an EMPor a trip through an [unloved] microwave would screw it up enough but more likely this sort of problem could be best accomplished with some really rough shaking or something.
posted by Songdog at 8:29 AM on August 3, 2006

Or it might have just stopped working. Laptop hard drives have a rough time from all the lugging about, and old ones do just die spontaneously sometimes.
posted by flabdablet at 8:52 AM on August 3, 2006

The old 'don't put magnets near computers' thing was only because floppy discs are easily scrambled by magnets. Not hard drives.
posted by cellphone at 10:57 AM on August 3, 2006

If you open up a disk drive you will find very powerful rare earth magnets that are part of the voice coil actuator that moves the arm for the head. Associated with the permanent magnets is a magnetic coil with a varying magnetic field that is used to move the arm back an forth. If you take out the rare earth magnets and stick them to your refrigerator, they are so strong that you almost need a screwdriver to pry them off. You also have magnets and magnetic coils in the motor that spins the platters. All of these magnets are positioned within a quarter inch of the disks yet do no harm. It is not likely that a weak magnetic clasp outside of the case would have any effect.

As others pointed out the heads on a drive fly only 0.5 micro inches above the platter. Compare this to 2000 micro inches for the diameter of a human hair. This small distance is required to generate the field strength to read and write the disk.

Your laptop drive could have failed for any number of reasons, but not because of an external magnet.
posted by JackFlash at 11:01 AM on August 3, 2006

The old 'don't put magnets near computers' thing was only because floppy discs are easily scrambled by magnets. Not hard drives.

Don't forget CRTs, which are easily damaged by magnets of all kinds. Though, to be fair, most modern CRTs include a degaussing option in their menus to fix most magnet-induced damage.
posted by odinsdream at 11:11 AM on August 3, 2006

JackFlash, thanks for confirming that the rare earth magnets are in the motor/servo mechanisms (and not in the heads). Those are certainly some powerful magnets, and damned close to the magnetic granules that store the data.
posted by Songdog at 11:19 AM on August 3, 2006

flabdablet writes "Or it might have just stopped working. Laptop hard drives have a rough time from all the lugging about, and old ones do just die spontaneously sometimes."

Amen. I'm not even clear on how he would sabotage the hard drive. Shake the computer? If I wanted a hard drive to fail on me, I would just use it for a few years. It's the most fragile component in the computer.
posted by mr_roboto at 11:40 AM on August 3, 2006

Agreed. 543DoublePlay, you've given no evidence of foul play. Most likely your colleague's computer just stopped working. You've offered no reason to assume he damaged it.
posted by Songdog at 12:01 PM on August 3, 2006

My iPod mini case has supermagnets as a clasp for the flip-up cover. It's still functional. I've also placed the iPod in its case on my iBook, and the iBook's HD is still functional.

And I just realized that iLabelling is a iBloody iStupid way to name a product.
posted by five fresh fish at 6:38 PM on August 3, 2006

iAgree.
posted by poweredbybeard at 11:59 AM on August 4, 2006