Sunday, 2 June 2013

21st Century Myths - Magnets and Black Screens


Last Christmas I bought a lot of those little neodymium magnet balls for my partner. Not the now-dead expensive Buckyballs but the generic cheap ones cause he'll be bored of them in a month. He put them on his desk, and I instinctively said "keep them away from your PC!", because everyone knows that magnets wipe hard drives, credit cards, and robot memories. Then it occurred to me that my previously-held belief in the data-destroying powers of magnets may be outdated, and quite possibly based on nothing more than an episode of Breaking Bad. Is there any reason for your data to fear the magnet? 

Dan's balls.

The key is coercivity, the degree to which you can demagnetise a magnetic substance. You can measure coercivity using a magnetometer, which has 'Magneto' in it and is therefore great. If you want to erase data, you need a magnet with a higher magnetic field than the coercivity of the drive. That's straightforward enough in theory, but in practice it's oddly hard to find out what the coercivity of a hard drive is, partly because the number is increasing all the time. At most it's 5000 Oe, but 2500 seems about average. Most credit or debit cards are around the 300 Oe mark, for comparison.

I spoke to magnet expert and engineer Michael Paul of http://www.kjmagnetics.com/ who told me that yes, little spherical magnets can wipe or corrupt the data on the magnetic strip of a credit card, if you wipe them along the surface. "The good news", he said "is that the field strength drops really quickly as you get farther away from the magnet. A magnet an inch away from the card probably won't affect it at all". Phew! But what about bigger magnets and hard drives, as per Breaking Bad?

Michael has actually conducted some tests with some big neodymium magnets and failed to affect the data in a hard drive. He told me, 

"the coercivity of modern hard drives is much higher than old floppy discs or VHS tapes. You need an incredibly strong field to demagnetize it. If you rub a magnet right on the surface of the hard drive platter itself, that should produce enough field strength at the drive. Of course, if you have already disassembled it that far, you could just as easily scratch it up or drill a hole in it if your intention is to destroy data". 

In his opinion, it's not possible to effectively wipe or scramble the data on a hard drive with powerful magnets without disassembling it. So much for conventional wisdom.

Another bit of received wisdom that doesn't seem to go away, a long-believed truth in the energy-saving powers of the black screen. I first heard about this several years ago when a link to 'black Google' was doing the rounds. Based on the theory that white pixels use more energy to display than black ones, the origin seemed to be a Lawrence Berkeley paper which at best is now woefully outdated. 

"But is it Y2K compliant?"
Back in 2001 the researchers looked at mostly CRT monitors and a few LCD monitors, which already tells us something about the uselessness of this data. It's absolutely the case that for the CRT monitors, less energy was used displaying an entirely black screen, but for LCD monitors the effect disappeared. Even the researchers acknowledged that. So anyone using an LCD monitor with black screen settings, you might mean well but the resulting eye strain probably outweighs any potential environmental benefits.


A version of this article first appeared in Custom PC Magazine in January 2013.