What are the effects of magnets on modern computers?

[warbean]

I have had some conversations with friends altely about magnetic fields and their effects on computers and CRT monitors. Apparently, some of them argue that the prime rule of keeping them away from disk storing devices is a relic of the past, and that the latest storage media can resist all but the strongest of fields. I went to FRYs yesterday and bought a small screwdriver to work on my computer. Would you believe that it was one of those double ended ones, with a magnet (ostensibly to pick up loose screws) on the end apart from the driver?

If computer equipment is as sensitive to magnes as some people suggest, I doubt such a device would have ever made it to market. Anyone have any opinions on this? (If only just to keep me from freaking out that I damaged my computer by working on it with that stupid screwdriver!)

 

[Mark R]

It depends how significant the magnetic field is.

The first device that would be affected would be a CRT monitor - even a relatively weak magnet will be able to deflect the electron beam causing distortion of the shape and colour of the image. This is a temporary effect - remove the magnetic field and the distortion will go. If it doesn't go, then activating the monitor's degauss function will fix it. The magnetic field from desk fans can cause very annoying rippling and shimmering of the image.

The magnetic surface on hard drives has extremely high magnetic strenght (coercivity), at least as strong as the strongest magnets available to buy. This means that even placing one of those neodymium 'supermagnets' on a hard drive would be unlikely to destroy the data on the disk. However, the seek mechanism is very precise, and electromagnetically operated, so disturbing the field with one of these 'supermagnets' could cause seek failures, or slow seeking.

At very high field strength (e.g. in an MRI scanner room), the hard drive would be damaged - either by magnetic forces causing mechanical damage (warping or breaking) or by erasing the data on the platters, additionally, fans would start to run slow or stop operating.

At even higher field stregnths (e.g. positioned within an MRI scanner), assuming that you had stripped the PC of any iron or steel parts, the electronics in the PC would stop operating (specifically, the voltage regulators would stop working, or more likely would fail with a spectacular release of smoke and sparks - this includes the PSU).

 

[randay]

A recent article I read from somewhere said that the case of a harddrive shields it from magnetic fields. It was an article about erasing data quickly and easily, they made a device that would erase a harddrive by just using super powerful static magnets that could overcome the shielding. Also have you ever taken apart a harddrive? They have super powerful magnets inside them anyway, so im guessing harddrives arent all that sensitive to magnetic fields.

For all practical occurances of a magnetic field near a computer, I wouldnt be worried. Of course I wouldnt want to find out the hard way either.

A magnetic-tipped screwdriver is a must when working with computers, you could do a lot more damage by losing a screw and having it short some circuit on your computer then by having the screwdriver go near a harddrive for a few seconds.

 

[byosys]

Originally posted by: randay
Also have you ever taken apart a harddrive? They have super powerful magnets inside them anyway, so im guessing harddrives arent all that sensitive to magnetic fields.

(Somewhat) wrong. The drive platters (where the data is actually stored) and the read/write heads (when in operation) are very sensitive to general magnetic feilds. The reason drive makers can put strong magnets inside of a drive is because they are placed very carefully so the magnetic feilds don't erase the platters. If you took an open hard drive and casually swiped a magnet over a platter, you would erase all of the data on that platter.

That said, I've used magnetic tipped screwdrivers to build 3 or so computers with no ill effects. I didn't go running the screw driver over different parts, so YMMV.

 

[randay]

Originally posted by: byosys(Somewhat) wrong. The drive platters (where the data is actually stored) and the read/write heads (when in operation) are very sensitive to general magnetic feilds. The reason drive makers can put strong magnets inside of a drive is because they are placed very carefully so the magnetic feilds don't erase the platters. If you took an open hard drive and casually swiped a magnet over a platter, you would erase all of the data on that platter.

That said, I've used magnetic tipped screwdrivers to build 3 or so computers with no ill effects. I didn't go running the screw driver over different parts, so YMMV.

What I meant was that overall a (complete)harddrive is not sensitive to your everyday household magnetic fields. Of course the platters have to be sensitive to magnetic fields in order to be writable. Still there are the two very strong magnets that drive the arm with the heads on it, and I dont believe that the platter is completely shielded from the magnetic field of those magnets. So there is probably something going on there that I cannot explain.

 

[maluckey]

I tested this theory of HDD erasure and computer hardware sensitivity (not very svientifically, but effectively nonetheless) with an 80GB Maxtor 7200 RPM HDD that was in good working condition. I ran an 8 pound speaker magnet (from a large Cerwin Vega speaker) everywhich way that I could, around the HDD, then installed and tested the drive. I was surprised that it did exactly nothing at all.

The same could not be said for the monitor. It had to be degaussed immediately!!

 

[BrownTown]

clearly the hard drive can be written/erased by a not too considerably madnetic field since that is what is doen when you write soemthing to the drive. I'd image a good electromagnet would be able to erase it pretty easily, but a small permenant magnet probably not.

 

[patentman]

Originally posted by: Mark R
The magnetic surface on hard drives has extremely high magnetic strenght (coercivity), at least as strong as the strongest magnets available to buy. This means that even placing one of those neodymium 'supermagnets' on a hard drive would be unlikely to destroy the data on the disk. However, the seek mechanism is very precise, and electromagnetically operated, so disturbing the field with one of these 'supermagnets' could cause seek failures, or slow seeking.

I have to disagree with you here. The average hard drive utilizes one or more magnetic recording layers that have magnetic domains oriented in the plane of the platter (so called longitudinal media). The magnetic layers in these drives are typically manufactured from a Cobalt Chromium based alloy that has a coercivity of a few hundred oerstead (Coercivity, for those who don't know, is a relative indication of how strongly magentic domains are oriented in a particular direction, higher coercivity indicates that the domains are more strongly fixed in a particular direction). In general, coercivity decreases with decreases in grain size and increases in temperature.

Coercivity enhancing elements, e.g. Ruthenium and Platinum have been added to Cobalt based magentic layer in an effort to maintin the integrity of data on the disk as recording density has increased. While this approach has met with some success, it does have its limits. Specifically, as magentic grains get closer together, each grain is subjected to the magnetic fields of the surrounding grains, a phenomenon known as intergranular exchange coupling. As the grains get closer together, the effect becomes so great as to destabilize the domain to such an extent that data cannot be reliably recorded. Thus, even though the magnetic field exerted by each grain is very weak in the grand scheme of things, it can still destabilize the magnetic domains of the recording layer.

Seagates "new" perpendiucar (it was in development 20 years ago) hard drives also use a CoCr based magnetic layer, but the layer is deposited using oblique chemical vapor deposition, a process that allows the grains to grow "vertically" (actually at about an 80 degree angle) from the surface of the layer. Even in this media, intergranular exchange coupling is an issue.

Ultimately it comes to the strength of the magneti and the distance from the platter, as well as shielding involved. As you should know, magnetic field strength decreases as the distance from its origin increases....thus, a strong magent will exert more force on a hard drive platter then a weak magnet at any given distance..... However, as mentioned above, even a weak magnet can alter the orientation of domains in a magnetic layer if it is in close enough proximity.

Oh...I used to examine patent applications drawn towards magentic recording media and magnetic laminates at the USPTO, thats why I know this stuff.

 

[patentman]

Originally posted by: randay
A recent article I read from somewhere said that the case of a harddrive shields it from magnetic fields. It was an article about erasing data quickly and easily, they made a device that would erase a harddrive by just using super powerful static magnets that could overcome the shielding. Also have you ever taken apart a harddrive? They have super powerful magnets inside them anyway, so im guessing harddrives arent all that sensitive to magnetic fields.

Actually, the only truly "strong" magnet in a hard disk is the read/write head, which is technically a "soft" magnetic material. Most of the other magnetic materials in a hard disk are weakly ferromagnetic, e.g. CoCr, Cr, Ni, FeCr etc....