It’s such an oft repeated warning that it’s firmly embedded in nerd lore: bring a magnet anywhere near your precious computer and suffer the dire consequences. But is true? Is your computer one run in with a novelty magnet away from digital death?

Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-drive grouping of Q&A web sites.

The Question

Although the anti-magnet rule has been repeated so often as to be law, is it actually a hard and fast rule of hardware safety? SuperUser reader Aequitarum Custos wanted to get to the bottom of it all:

When I first started using computers, law of the land in computer class was never bring magnets near anything computer related, lest you lose all your data or screw up your monitor. Now I am pretty sure magnets will still royally mess up a standard hard drive, and I know for a fact they screw up a CRT monitor. Though I am also pretty sure they do not screw up a LCD monitor? Now I have my phone which uses magnets to determine if it’s docked, and it made me wonder. Is it the power of the magnet preventing data loss or the sheer fact that whatever memory type in the phone is immune to it? What about ear buds, as I know those have tiny magnets in them. Are those capable of damaging any electronic device currently in use? I’m wondering if I’m being paranoid, but I really am not sure what magnets will damage and what they won’t! Is there a list, or rule of thumb for determining what will be hurt by magnets and what won’t be?

Anyone who ever turned on a desk fan near or atop their old CRT monitor can certainly attest that something was happening, as indicated by the wild pattern of rainbows that erupt across the screen, but was that something permanent damage?

The Answers

SuperUser contributor Synetech explains:

A list or rule? Sure, anything that uses electro-magnetism to function could, and would be affected by magnets. The question is what the detrimental effects, if any, would be and how strong and close do the magnets need to be. Generally the two most questioned items are the monitor and disk drives. LCD/LED monitors are not generally susceptible to magnetic interference like CRTs are because they function completely differently (remember, CRTs use magnets to deflect the electron beam, so an external magnet would obviously mess with that). Hard-drives are also not affected by magnets because of the way they function. You can research the details on how hard-drives work for a more thorough understanding, but the easy answer is that there is a very powerful magnet inside each hard-drive that controls the read-write head’s movement. That’s why some people like to rip open dead drives to get at the sweet, gooey super-strong magnet inside. If that magnet that is inside the drive, right beside the platters, and it doesn’t wipe them, then any magnet that you are likely to have around isn’t going to. As for flash drives, they are a different technology altogether so they are not going to get erased. There is one component however that is indeed affected by magnets that most people miss: cables. While many cables are shielded, some are not and thus susceptible to a magnetic field. For example, a cable connecting the sound card to the speaker may be shielded, but the little cable connecting the CD/DVD drive to the sound card usually isn’t and ingress of a magnetic field could cause interference. Or, while rounded IDE cables (especially for IDE133) are usually shielded, ribbons usually aren’t and even at speeds of 66/100 could be affected enough to cause some corruption or at least reduce performance due to re-tried reads/writes. I would say that modern systems are not really vulnerable anymore because as time progresses, science and knowledge advances, but unfortunately that’s not sufficient. While that may be true, in the old days things were done right a lot more than today with all the cut corners and cost-reducing measures (eg NVIDIA’s “Bumpgate”). Anyway, the point is that when it comes to modern computers (I’m counting floppy disks as not-modern), you don’t really need to worry about magnets. You can breath a sigh of relief. :)

While that answers the meat of the inquiry, you’d have to be wildly negligent with an extremely powerful magnet to cause any real damage, contributor dmckee offers an example of the effects of working around a very powerful research magnet:

I recall sitting at a computer on a major particle physics experiment when the big (10x5x3 meters, >100 tons) dipole magnet was being tested about 40 meters away. As they ramped it up the display would twist to one side by about 10 degrees. Hit “degauss” on the monitor front panel, ::blur:: then return and all would be well. Later, they’d ramp down, and the monitor would twist the other way…good times. Leave you wallet in your pocket and walk into the hall while they were doing that and you’d loose the data on the magnetic stripes on all your cards…bad times.

If a magnet that powerful sitting next to the monitor and computer tower couldn’t permanently decommission the machine, then surely a magnetic business card absentmindedly slapped on the side of a computer case is little case for alarm.

Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.