Fatal Attraction: Lovely collection, really, but it does not belong anywhere near magnetic storage media Friday brings the promise of a weekend free from the work laptop but likely shackled to the personal laptop instead. Kick off your two days of downtime with another tale from those brave enough to be On Call. Today's story comes from a reader Regomised as "Elliot" who was spending the mid-noughties gainfully employed as third- …
Yes!!!
I often tell people about the time I worked supporting sub POs and one particular office had a Unix box that failed three times. Each time i had sent an engineer out to swap the box out (Unix boxes don't fail via the OS - it is usually hardware - so faffing about onsite wastes valuable engineer and PO time).
After the third swapout I managed to secure authority from management to have the engineer stay on site as the boxes always failed after a only a few hours.
The sub Post Master's wife made a cuppa for the engineer and while he and the PM chatted, she set about festooning the Unix box with fridge magnets which she had removed from the old box prior to the scheduled engineer's visit...
Good to see I'm not the only victim of that!
Upvoted - I've seen it time and again in bookies, usually when there isn't much "sport" happening. They have magnets to hold newspapers to metal boards running around the shop so people don't even have to bother unfolding the paper to find whatever it is they look for, and when it's quiet and the paper is a bit thin, they usually have magnets that aren't being used.
Rather than leave them out where people can steal them, a few enterprising shop staff stick them on top of their M72/M73 small form factor PCs, and then wonder why the HDD crashes and dies.
That one came up on Scott Adams' mailing list many years ago (i.e. well before "chip 'n pin", contactless, etc).
To cut a long story short, an IT bloke at a hospital bet a particularly annoying sales droid that he couldn't chuck his wallet clean through the hole in the "doughnut" from the doorway.
Turned out that he could and it was well worth $10 imagining how much fun he was going to have checking out of his hotel the following morning.
Ohh, the MRI people I had to see had a *lot* of signage up, and not only that, but you were required to strip to your skivvies and put one of their lab-provided getups (I dunno how to describe the kit) on. No metal, no cards, no nothing. Pencil and paper was ok. Once you went through the door that led to the MRI chamber, all bets were off about the safety of anything remotely magnetic in your hands.
And it was glorious to stand next to what was the most powerful magnet in the UK at the time. :-)
I got to tour a research place some years back, where they used MRI and other devices. We didn't have to change clothes, but there was a very detailed going-over for anything metallic, to be left back in the meeting room. "Oh, and please let us know about any medical implants you may have before we go on..."
with good reason.
I had an MRI a few years go, I did explain I had had an accident where a piece of swarf managed to get around my safety glasses and might still be in my eye 20 years earlier when grinding off rusted exhaust brackets on an old range rover. I was sent for an x-ray which showed nothing.
this generated lot's of mockery from my wife. 2 years later I developed a cataract. in the space of 6 weeks I went from good vision to blind in one eye. I had sought medical treatment as son as things started to change but before I could have the lens replaced it was completely opaque.
The consultant looking into the eye could see the hole in the lens caused by the piece of swarf. It had sat there happily for 20 years until the MRI moved it and it then gradually drilled its way through the lens. If you do need an MRI insist on an eye exam with a microscope if you have any indication you've suffered a similar injury. If you do suffer such an injury in the future make sure that you visit a specialist eye department where they can use a microscope to view the eye. Whilst the operation to replace the lens completed successfully I've since had to have laser surgery to correct cloudiness issues with the new lens
We had the opposite problem in the early nineties at our university library. We were used to handing our floppies to the guards at the entrance before walking through the presumably magnetic scanner so that they wouldn't be wiped.
However the guards weren't familiar with how CD-ROMs were encoded and insisted that he take these as well. In the end, the constant explanations got nowhere and it was just easier to give him the CD-ROMs.
I also had an encounter with a magnet issue. One of the wife's friends had a son who called me one day about his Mac laptop. It would seem that it wasn't starting any more. I alerted him to the fact that I didn't know all that much about the Mac software environment, but agreed to go take a look.
When I got to his room, I started checking out the laptop and asked him when the issue had started. His answer was to point to a large lump of metal, about the size of my fist, in the form of a cylinder and said that it had fallen on the keyboard. I took one look at the thing, with its nails, paper clips and other assorted "decorations" clinging to it and told him that his disk was wiped and probably dead. He looked at me as if I was telling him the sky was green and asked me why.
That's when I had to explain to him about magnetic storage and how it doesn't do well with ginormous magnets in the immediate vicinity.
So yeah, not knowing about cassette tapes is likely a cause of ignorance of the issue.
Speaking from personal experience: a smartphone or equivalent would do the same.
I first noticed this when I put a smartphone on the left side of a 2012 MacBook Pro's palm rest and had it suddenly go to sleep, only to wake up again when I removed the smartphone.
Makes me wonder what level of magnetic field in an office would be sufficient to put all MacBooks to sleep.
I saw that with a BlackBerry and a lady with a magnetic bracelet. She complained that her Bold was cutting out often and it needed replacing. After she had another one provided and the same thing happened, various theories were suggested. Then as she handed back the replacement her bangle picked up some paperclips and the connection was made.
The bangle we were told was made of "rare earth elements" and protected her from things. Can't remember what it was it protected her from but suspect it might have been from ever being short of paperclips.
A student at a school where I worked would take all her projects home with her on floppy over holidays. She would inevitably come to me after class resumed with a corrupt disk asking me for help in retrieving files. I initially thought she was buying some cheap disks but finally asked her about what she did when she got home and what happened to her disk over the break. Turns out she was afraid of losing the thing and stuck it on her fidge with a magnet as soon as she walked through the door so she would know where it was when she got ready to go back to school. She never lost the disk, just the contents.
Only I knew what I was doing - I was upgrading FoxPro versions via M$ and they wanted a photocopy of master disk 1 as proof of previous purchase. in order to give me the discount. So off I trotted to the local library to perform said copy.
The kindly librarian pointed out I was doing The Wrong Thing. Which I wasn't really.
You would be surprised at the actual strength of an external field that is needed to upset a hard drive - even back in the days of the noughties and GMR media I cannot see a thousand fridge magnets upsetting things. The field strength on the write heads is enormous, and thought the read heads have a weaker response, there is a drive case shielding it, and a main PC case, and then the distance they are away..... plus the fields from internal PSU's which are not inconsiderable and don't bother the average PC one jot...
Well not to doubt you, but we have at least a few tales here in the comments of exactly this happening, so it does seem like its real.
Notice that none of them speak about damage to the harddrive itself, just the occasional bit here and there being flipped, and causing disk corruption, which certainly seems plausible. Whilst the read and write heads are pretty well protected, the platter itself isnt overly EMC protected...
I've tried to deliberately corrupt several types of magnetic medium using rare-earth magnets, degaussing coils and the like, and never managed to succeed, even with floppy disks.
For hard disk drives, you not only have the steel case of the computer itself (it needs to be steel or another ferrous metal for the magnets to stick, yes?) but the metal chassis and cover of the drive itself. Even non-ferrous metals tend to disrupt magnetic fields due to induced eddy currents.
The other thing I would like to point out is that if it were single bits being corrupted, the error-correction in the disk controller would easily fix them. If it were multiple bits, more than the ECC could correct, then the read would be retried, and if that failed, the sector would be marked bad, and the error would be fed up the chain to the OS and the requesting program. The chance of a silent read failure is exceptionally low, measured in the one in billions (this is a guess, it is documented for most drive models) of read operations.
Hard disk drives suffer from bit-rot all the time, so the ECC is pretty robust.
It seems incredibly unlikely that the fridge magnets were the cause of the problem, although I'm not going to try to suggest an alternative.
"It seems incredibly unlikely that the fridge magnets were the cause of the problem, although I'm not going to try to suggest an alternative."
I've suggested an alternative elsewhere - it's not unheard of for disks to fail. Other alternative is the first 2 technicians changed the drive as standard, the 3rd technician changed the drive and IDE cable as standard (and then took some fridge magnets off the case).
Either way, this is how vaccine scare-mongering starts. "I had a cold after I received my vaccine"
This may vary but I tried waving a few fridge magnets past each other, fridge face to fridge face (back to back, I suppose). These seem to have typically a flat disc of magnet stuff maybe 1.5cm diameter, and it appears that the centre of the disc is one pole, and the edge of the disc is the other pole. So, face to face, they repel, but oriented like a simple "Venn diagram", they attract.
https://science.howstuffworks.com/math-concepts/venn-diagram.htm
Magnets have a "field shape". the massively powerful magnet inside the drive is shaped in such a way that its field lines don't intersect the head or the platter. thus doesn't damage the drive.
A fridge magnet can however magnetize the outside of the HDD case, which in turn passes its field lines THROUGH the platter (and through the coil as the head passes nearby).
Not sufficient to destroy the platter, but can flip a few critical bits.
I doubt it's a steel lid.
I just went and tested one of my old IDE disks that I have lying around. A Maxtor DiamondMax Plus 9, 80GB ATA (hey, just big enough for Windows 11 !).
I scooped it up and went to our fridge, where I proceeded to try and stick a fridge magnet to it.
No luck, they all fell off as if it was made of wood.
I don't know what to conclude from that, though.
There is a gap in the centre of the magnet pair because you know the field coil has to be there. The permittivity of free air being what it isn't the field that does escape there goes a long way...
Also I think you would have a hard time magnetising the aluminium alloy that most drives cases are made of.
This whole story comes from a misunderstanding of magentism and "well it seems reasonable" I'm fairly certain that you could place a fridge magnet directly on the disk platter itself and there would be bugger all effect. A fridge magnet might be as much as 5mT - you will be talking about write strengths several orders of magniude larger than that. And thats assuming you can put the magnet on the platter.
For reasons that are obvious I won't say where, but I played a lot with wanting to make HDD instantly - or as near instantly as possible as unreadable as possible. We had a brief, and some big coils and big high current batteries that were from a long steel tube thing that used to travel undersea... and even then it wouldnt even touch a bag of modern hard drives that were ejected and placed inside the coil. We eventually recommended that the client buy only glass platter drives and if needed, stack them in a column and use a 7.62mm fired down the stack to be sure...
A large commercial neodymium magnet on the drive casing - and I mean a large one - the sort of thing that will stick to a thick steel plate and need a good 5kg to pull it off - that will stop it working because the magnetic flux lifts the heads off the disk by attracting them together. Works when removed though.
Attached to the case it'll do bugger all. I've only ever stopped a machine once like this with a magent so chunky it would amputate a finger if you get between it and some iron - and even that stopped the PC only by tugging so hard on the baseplate it shorted the motherboard out.
The HDD was just fine.
I'm not saying that there wasnt something going on in the article - but it wasnt some poxy fridge magnet.
> ...wanting to make HDD instantly ....as unreadable as possible. ...some big coils and big high current batteries ....wouldnt even touch a bag of modern hard drives..... use a 7.62mm....
Clear tap water has low electrical conductivity, and HDD circuit impedances are just a few Ohms. I bet some online guys (this was before ElReg was founded) that a HDD would work a while under water. Clean plastic tub, long power and data wires to a live PC. Well, I lost, with pleasure. It bubbled furiously and the data erred in seconds. A week on a warm air vent and it still would not read. Very quick and cheaper than a bullet.
{Yes yes, KGB or CIA would whip out the platter-stack and read all.}
For obvious reasons Im not going to finger the client, but people pulling the platter - or indeed just using a commercial disc recovery service was the major worry. For mass "quick" disposal they did go with the 7.62 which will probably tell you enough about they type of organisation, the real emergency treatment involved a fire axe or hammer if they had to do it right then and now.
Modern SSD's I suspect are a little more tricky to get gone properly especially if soldered on a motherboard. I suspect incineration would be the quick solution...
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I had built up a batch of 20-odd disks removed from a Proliant ML750 which was being scrapped but we wanted to ensure the disks got special treatment, I took them down to the maintenance engineers and asked them to drill holes through with the drill stand in the area where the platters were and through the pcb. He called me back and said come and get the rest, I’ve managed 2 of them, any more and I’ll have to start charging you for broken drill bits.
Fast forward 20 years and now I get them destroyed by a company that brings in machine no bigger than a photocopier but it has a scissoring blades at one end of a slow conveyor. You put the disk on one end of the belt, a camera takes a picture of the disk’s barcodes etc, the the blades come down and slowly slice the disk into bits the size of Twix bars. It’s awesome to watch and the crunching is totally satisfying.
The bits then drop into plastic boxes, where - because the disks were no longer whole maybe - I expected them to miraculously lose weight. No. I nearly pulled my kipper lifting the first one with the equivalent of 15 hard disks in it.
"Modern SSD's I suspect are a little more tricky to get gone properly especially if soldered on a motherboard. I suspect incineration would be the quick solution..."
At least one of our clients has a shredder. It makes quick work of 3.5" HDDs. Anything smaller is gone in an instant. And yes, it will eat laptops and tablets too. Although generally they only put the motherboards through if it's soldered on storage, otherwise it's just the drives. The rest is sometimes saved for spares, eg laptop keyboards and LCD panels. Out of warranty user damage such as damaged keyboards and cracked LCD panels can be expensive and some parts currently have long lead time.
> Exactly. This is where this story always falls down - the weak fridge magnet outside can totally trash a drive but the rare earth neodymium one inside has no effect at all....
mu-metal is the difference, those rare earth neodymium magnets have a mu-metal backing to isolate the magnetic field away from the spinning platters. And it works very well.
This problem was specific to a time when the error correction in drives was much less than it is today (today every single disk read even SSD's has multiple error bits that are corrected). It was during a brief window when steel plates above the platters were removed as a cost saving exercise. It would have been before the change to perpendicular magnetic recording technology, so back when "conventional longitudinal recording technology" was king of the roost.
One of the problems in the IT world is that fundamental knowledge of electromagnetic theory and bipolar junction transistor theory are no longer required, giving rise to massive amounts of misunderstanding and subsequent superstition when it comes to things like having a fridge magnet on a steel PC case.
When I was at uni, I used to run my own NMR samples. The NMR machine in question was a bit weedy by today's standards, running at 440 MHz, so the field strength was only about 10 T.
The Unix machine that ran the thing, which was in the same room about 3-4 metres away didn't seem too bothered by it, nor by the electromagnetic pulses the machine emits.
Fridge magnets, on the other hand, have field strengths measured in mT.
The CRTs would be much more prone to the effects of an NMR machine. The interaction of radio pulses and electron beams springs to mind. The heavy shielding on the monitor will have been to save the poor operator's eyesight because otherwise the image would be wobbling all round the place.
CRTs are much more sensitive to such interference, which can easily be demonstrated by moving a weak magnet over the surface and observing the pretty patterns made by the field lines.
IIRC, the machine controlling the NMR (and this was in the mid '90s, so my memory isn't quite as crisp as it might be) was a pretty standard SGI box. I think they probably angled the monitor so it was in line with the field lines, not perpendicular, to reduce sideways wobble. i.e. facing away from the big silver thing in the middle of the room.
That's a cracking point I hadn't considered - where did CRTs (aka honkingly large electro magnets) previously sit in the days before tower PCs? Right on top of the desktop PC. Again, hard disks coped just fine with that - but not with a weak fridge magnet that can barely hold its own weight.
A mate back in the uni days had exactly this. His halls room was quite nearby to the university NMR centre (this was UniNotts in the 90s, where they pioneered the things under Prof Sir Peter Mansfield).
His room was basically a couple of hundred meters from the 6T magnet NMR machine in the building, and he could always tell when they were running at full tilt as both his TV and computer CRT monitor went temporarily screwy and occasionally even needed degausing to remove all the pretty colours that were left behind after some runs.
Never once did he have any issues with floppy disk corruption though, at least that he mentioned to me.
I think the magnetic field and high voltage is (meant to be) at the "back" of a cathode ray tube display, but PC disk drives are installed at the front - away from the PSU as well.
...which way around were problems with "home computers" like Apple II and certain TVs or monitors with and without built-in shielding? No picture, or no disks? Or both?
These stories won't be made up 100 percent of the time, surely?
"These stories won't be made up 100 percent of the time, surely?"
No, but, they'll certainly be falsely attributable. I've had many a hard drive fail over the year, I've never thought to attribute a fridge magnet to it though. There are millions of hard drive failures a year. There are millions of people with some sort of fridge magnet on their PC (I've already mentioned, my case has removeable fan filters that are magnetic). The collision of these events is not significant.
To specify, I think the claim isn't that the non-standard magnet pulls all of the bits on the disc around, but that it interferes with the drive writing process.
The type of disc write that depends on heating up the disc locally, if that isn't all of them, also could be affected.
I should mention also that some of these magnets are of much greater magnitude than others, even leaving out ones taken from inside disc drives or earphones that may be industrial-strength.
"Fridge magnets, on the other hand, have field strengths measured in mT."
Per Wikipedia's Tesla (unit) page, typically around 5 mT.
For anyone else reading this, a 10 Tesla field is outrageously powerful. For reference, the field at the surface of a neodymium magnet is around 1.25 T. World record for continuous field magnets is 45 T. Wikipedia tells me "The strongest fields encountered from permanent magnets on Earth are from Halbach spheres and can be over 4.5 T." and then goes on to note the creation of a 1200 T field in 2018, lasting only 100 uS.
Anybody who works on NMRs or MRIs have any good stories, or links to good "what not to do" videos?
Yeah I'm suspecting a case of cogito ergo sum. I salvage the impressively strong magnets from inside the HDD whenever I dispose of one (they're terrific for finding screws and therefore studs in a wall for example).
While there are more examples in here of it happening, consider how many unreported examples there are of fridge magnets where it doesn't cause issues, because it's not worth reporting or noticing. Here's mine - for several years, I had a mini network switch with magnet feet clinging to the side of my case without data corruption. Here's my other one - all the fan dust filters on my current machine are held in place by virtue of being giant fridge magnets.
I also doubt that this user is unique. Fridge magnets have been put users' PCs in an office environment since I can remember.
I've also been told to never use a magnetised screwdriver near a computer, let alone near a harddrive. When I was building PCs as a day job however, we all had magnetised screwdrivers, and never once a problem.
Mind you, that job taught me that PC components are usually a lot more robust than people give them credit for. For example;
Should you drop a harddrive from head height onto a wooden floor? No.
But will it survive? Turns out, yes. Most of the time at least, unless you're unlucky and it lands on the connectors.
Definitely the latter, at least for them corrupting the hard disk. Potentially corrupting files en-route to the disk - maybe even a keyboard cable - but if it were the disk itself it'd be more than just a few Word docs. Looking at the age of the story, Word in those days was more than capable of corrupting its own output...
Correlation is not causation.
You say that, but I remember the time I had a faulty disk in an old SGI system. I placed the call to support, and was told, by the engineer on the phone, and I quote (to the best of my memory)....
Take out the disk.
Bang it on the table, edge on.
No, I said BANG IT. I want to hear the disk hitting the table.
I hit the thing so hard on the table I put a dent in the table top.
Bloody thing span up and the system booted!
Quantum 105MB disks in early SPARCstations were notorious for that. They'd run for years non-stop, but once they'd stopped spinning they wouldn't restart because the lubricant had thickened and become sticky. Lifting the front of the pizza box up 3-4 inches & letting it drop back to the desk was the usual effective solution. Best followed by an fsck, just in case.
There was a story about a power company where that happened. Being a power company, they didn't pay electricity bills, so their computers were permanently turned on. Then they moved offices. If I remember right, hundreds of hard drives turned off for the first time in years. And the lubricating oil turns solid when that happens.
And yes, the solution for a few hundred machines was dropping them on the table which made the lubrication oil fluid again for a fraction of a second, then turning the computer on at the exactly right moment. Once the drives where spinning they were absolutely fine.
For one customer, we ended up supporting IBM 3274 controllers. They were usually tucked away in filthy places where right thinking people wouldn't venture.
Following a power outage, we visited one which wouldn't restart.
From the amount of muck inside it, we reckoned that its 8 inch floppy drive had last turned a spindle at least 8 years previously.
Luckily the config on the floppy read OK following drive replacement and careful cleaning.
"Lifting the front of the pizza box up 3-4 inches & letting it drop back to the desk was the usual effective solution."
And then pop the lid and press down on any socketed chips to make sure they were properly back in their sockets. Temperature change made the chip legs and the metal sockets expand and contract a tiny amount and they'd creep out of their sockets over time. "Doing the drop" was quite likely to further loosen any that have started to move and result in anything from not completing the POST to weird random errors.
IBM Spitfire drives (1-2.5G half height back in the early '90s) suffered from stiction. And this was the advice from the IBM hardware engineers as well.
Just had to unstick the head from the parking area of the disk to allow the disk to start spinning, and as long as the head was not damaged, the disk would be fine, at least for long enough to re-write the data to another disk.
The problem with these disks was the wrong lubricant being used for a number of batches, one that would vaporise and then condense on the platter when the disk was powered down, acting as a glue.
Same here. I had an old (new(ish) at the time) 40MB 1/2 height 5.25" HDD (Bigfoot?) that was out of the case standing vertically when the desk got jostled and it fell flat. If would have survived while not powered on is a moot point (it probably would not have), but it was actually spinning and in operation at the time. I nearly cried! That was a BIG drive for the time. (There were bigger, but that was high end server stuff and well out of my price range!) Worse, there was a lot of stuff on it and I was already living dangerously by running it on an RLL contraller instead of the proper MFM one so as to get 65MB out of it. Luckily it was mainly pirated games I could easily get again and not the boot drive :-)
Yes, particularly by the time period the story alleges to be set, the idea that some fridge magnets were corrupting the hard drive of a machine is silly. This is a layman's understanding of magnets and magnetic media.
Here's a website from a company who manufacture very strong magnets, outlining how they stuck two very large neodymium magnets to the case of the hard drive itself (not the case of the PC), and it did... absolutely nothing: https://www.kjmagnetics.com/blog.asp?p=hard-drive-destruction
Not a single file was impacted. And this is using rare-earth magnets so powerful that they literally come with a safety warning and cannot be separated by hand, placed within half an inch of the surface of the disk itself. A few 'Greetings from Torbay' fridge magnets stuck to the outside of the case are nothing in comparison.
I had a Wi-Fi card for a desktop in a room that I couldn't be bothered to cable up with ethernet.
The antenna was fixed to the case with a big magnet in its base. More powerful than a fridge magnet, couldnt just pull it off, had to slide it off the edge.
Never had any disc problems.
I once had one of those magnetic desk toys with the pile of little iron men that sit in a spiky head atop a plastic platform with a magnet inside. I was moving things around and it ended up sitting on my Mac book pro for all of 10 seconds before I realized that was a bad idea. it immediately died, the drive was toast.
luckily it was my Mac and not the machine I used for any real work
Not at all as bad as losing a drive. At work I use MacOS and Windows daily and on separate hardware. A few laptop generations back, I had run out of space at my desk, so, when I was done working on the Dell laptop, closed the lid, plopped the MacBook on top to continue work there. Flip open the lid, blank screen. What? Close lid, reopen. No change. It was working seconds ago! Must be the display brightness...
Jab middle finger on to power button to force reboot. Boots up, Mac happy sounds pling from the speakers. Blank screen. Fine. Grab the MacBook and trundle up to the IT walk-up support station to whinge about crappy logic boards build quality etc. Flip open screen... ta-da! All hunky dory.
Back at the desk, MacBook back on top of the Dell, flip screen... blank!
Yeah... turns out I am PEBCAK idiot. Both laptops were of similar design (same Foxconn factory) and both utilised a magnet for their keep screens closed feature. Magnets that are good enough to trigger the sensor on the top laptop that despite screen is physically in open position, the sensor indicator still indicates closed, prohibiting the screen from displaying anything. Lesson learned.
I have a classic 160GB iPod with a spinning drive. It's old but I was using it in the car back when I did regular commutes. I had a dashboard magnet, designed for holding a phone, and it would have been perfect for holding the iPod. I knew it probably wasn't going to like it, but I couldn't resist the temptation to try. Sure enough, it made a horrible noise, and the screen glitched out. For a few moments, I thought it was totally buggered, but it eventually sprang back to life with seemingly no permanent damage.
Suspect that it was the read heads being physically moved by the magnet. Also suspect it was a much stronger magnet than one designed to only hold the weight of the magnet.
I've managed to corrupt a classic iPod (to accelerate a warranty claim that was intermittent), but relied on it being a really strong neodymium placed directly on the iPod case (itself only 1-2mm away from the platters and read heads) and left to play for 12+ hours before it failed.
There's a lot to be said for making PC casings out of plastic or aluminium.
Just a thought - are fridge magnets all or predominantly magnetised with the same orientation? If they're random or better still each ha two poles with opposite orientation (like a horseshoe magnet) then the net field on the other side of the cover should be low to nil.
They're ... odd. Some "individual" magnets actually has a bunch of north and south poles alternating with each other. Side effect is probably to diminish the total field emitted. Others use a Halback array, which is a "spatially rotating pattern of magnetisation" producing a far stronger field on one side than the other.
https://en.wikipedia.org/wiki/Refrigerator_magnet
https://en.wikipedia.org/wiki/Halbach_array
Many moons ago, I witnessed a field engineer open the back of a piece of equipment, pull the diagnostic floppy (8", just to date myself) off the inside of the door where it was affixed with a magnet ... and the fucking thing still worked! Observing my surprise, he just shrugged and said "I know. I don't get it either. They did it this way for years before I got here. I don't ask questions, I just go by their playbook and collect my pay." He claimed to have seen several tens of these things, and the disk was only dead once ... and that was caused by a couple of rather obvious staple holes.
Magnetic media is a lot tougher than most people think. I would be absolutely astonished if something as weak as a fridge magnet could affect a hard drive. Even several tens of fridge magnets. I'd be even more shocked if a fridge magnet or magnets attached to a desktop PC's case could affect data in transit between CPU and drive media ... especially if the magnets were immobile.
With that said, I have heard this story many times over the years. But it has always been a FOAF telling it, not the person it supposedly happened to. And for the record, we tried on numerous occasions to cause the so-called corruption, with weak little fridge magnets all the way up to rare earth magnets. We observed no data corruption at all.
If anyone can tell me how to replicate these results I'll be more than happy to believe it is possible, but until then this is in Urban Legend territory.
> And for the record, we tried on numerous occasions to cause the so-called corruption
I sometimes dismantle old, dead, HDDs for the magnets. I have several of them stuck on the side of my PC as I write this. They have never caused any pr0q2w38iv dzzzzz that I have seen.
The only explanation I can come up with is that, in pointing out that the computer is supposedly fragile enough to be damaged by fridge magnets, the engineer has put the fear of $deity into the user, and they have stopped doing whatever it was that was causing the corruption as well. In the olden days, a lot of beige boxes went under desks, so it could be that they were tapping their feet against it, or something similar.
I remember a call from a secretary many years ago (1980s?) to say her 'foot rest' was falling apart. It turned out to be an ancient GPO badged (so many years pre-BT) 300bps dial-up modem the size of a PC and the casing had collapsed
It was still working!
She got something a bit more up to date, but only because they couldn't source a replacement case... all the other bits were still available! (good old fashioned descrete components... none of these new fangled 'integrated circuit' malarkey)
I have personally messed up an audio cassette tape with a magnet. But the magnet was more powerful than a fridge magnet, tapes are probably more susceptible than HD platters, and the magnet would have been MUCH closer than anything could get to a spinning platter.
The effect, weirdly, was to dampen (but not eliminate) the sound recorded on the tape.
Back in the last century a lot of people kept their stereo cassettes in the car door pockets, frequently next to the door speakers. The effect would be that after a while the tapes would sound more and more muffled.
Similar thing with video tapes stacked on top of stereo speakers as a lot of people kept all of their entertainment kit along one wall.
Many, many moons ago I left a genuine copy of Repton 2 (I think) for the BBC Micro on a desk at school. Dumb-arse that I was, I ran off to the next lesson without it. When I went back to retrieve it later in the day, some arse-wipe had used a biro to colour in the exposed disk surface.
Still managed to use a disk editor to rip a replacement working copy of the damaged disk.
Those disks really did take a lot to screw up (unless you're a knob like me who worked out how to change the writable size of the disk so low it wouldn't write anything and then give it to your mate to use to save his work).
<wipes nostalgic tear>
"The only way that I could find to reliably cause an error on demand was to make a hole through them with a hole punch."
I once came across that as a copy protection method. There was a carefully positioned extra hole in the disk where a bad sector would be caused. The software checked for the bad sector so making a copy didn't work because on the copy, the sector wasn't bad. (Easily bypassed, of course! I wasn't going to use the original on a daily basis!!)
The story went around in the 80's that trravelling on the tube i London would corrupt any magnetic media you were carrying - apparently the fields from the motors were rather strong. It was actually not tue, but we could use this excuse to travel by taxi, rather than tube, when working in the capital and get paid our expenses fr it.
The magnetic fields in a railway traction motor are intense, but they are also confined to specific closed paths within the motor. Otherwise the motor would be less efficient than it should be. However, underneath each motor coach of an electric multiple unit is control gear for the motors. Resistances and contactors in older units, operated by electromagnets, and making/breaking quite large currents (a thousand of amps or so at 600v - 750v). Arcy/sparky. This could have an interesting effect on electronic equipment a metre or so above, especially if the train car has/had a wooden floor, as many did. In 1963 aged 11 I went to Headquarter and General Supplies in Croydon and bought a battery-operated tape recorder for £4.19.6 and on the way home by train, tried it out. When I played back the recordings I made, I could hear track sounds, the motors starting after each station stop, etc, but also kind of hissy clicks, (like distant lightning on an AM radio) which I decided must be the EM interference from the control gear switching out the starting resistances for the DC motors. For any rail buffs, I was in a 1946-1951 built BR Southern Region 4-SUB multiple unit, but all electric trains up to around the 1980s used this technology.
"In 1963 aged 11 I went to Headquarter and General Supplies in Croydon and bought a battery-operated tape recorder for £4.19.6 and on the way home by train, tried it out. When I played back the recordings I made, I could hear track sounds, the motors starting after each station stop, etc, but also kind of hissy clicks, (like distant lightning on an AM radio) which I decided must be the EM interference from the control gear switching out the starting resistances for the DC motors. "
Believe it or not, here's a YouTube video of the very model. Very crude; erase was by a little magnet that pressed against the tape when the switch was at the 'record' position. The tape was driven by a little PM motor that turned the take up spool, and I guess the speed varied as the spool filled up, but you wouldn't notice that unless you played the tape on a proper machine.
https://www.youtube.com/watch?v=7uk2jZVYA1U
That's OK ... The 225 had a 1kW linear motor for a head actuator. It needed that kind of power to overcome the inertia of the 20 R/W heads to meet the sub-10ms seek times ... Or, rather, to overcome the inertia of the entire head tower, which weighed around two and a quarter pounds. One wonders what kind of magnetic fields were generated inside the drive when in operation ... I seriously doubt the Tube could match that inside a passenger car, at least not under normal operations.
I must admit it sounds more like an urban legend to me, too, but being an open-minded commentard I've got to ,,, well ... make a comment...
The disks in the story did not fail, did they? Rather, just some files were mangled (Word files - probably just because that's all the user was doing). Maybe it takes a lot less to flip an occasional bit, and possibly only when things change (so that doc contents get corrupted while Word and system libraries and such keep working). The SLAC comment was interesting and sounded relevant indeed, but then maybe even a strong uniform background component (let's not forget the Earth's field, either) would not have the same effect.
In short, a proper experiment is in order. No, I am not volunteering.
[*] Yes, I know, I suspect I might have mixed a TV show and a movie.
It probably happened, multiple failed disks isn't unheard of. Or perhaps the third engineer also replaces the IDE/SATA cable as standard where the first two engineers doesn't.
Some word files mangled, but (say) pagefile.sys carried on regardless? If every million bits was getting flipped, I'd expect to see random BSODs before I saw a bunch of .doc files corrupting.
Yes, those bulk tape erasers ran on AC to create a pulsing magnetic field. They worked quite well. I did once manage to partially damage a floppy disk by rotating a magnet multiple times around the path of the data tracks. It wasn't an especially strong magnet, but way stronger than a fridge magnet.
A colleague took a "spare' large magnet home as a toy for his son, intending to give him some drive-by physics tuition. He set him off to find out which things in the house were magnetic. Imagine the look on his face when told that the screen on the colour television wasn't magnetic and by the way there seems to be a fuzzy blob in the middle of it now ...
The degaussing coil that most TVs have had since the late 1960's should have fixed that issue after being turned on and off several times.
Before that, in order to fix it, you would have a TV technician come and wave a degausser, which was nothing more than a coil of wire with suitable current limiting device (like a PTC resistor) plugged into the mains, over the screen.
While working for Marconi I came across a 18" reel of very thin wire, which I simply put a mains plug on and used it to degauss all manner of displays over the years! I never even thought about putting a current limiter in there, such is the exuberance of youth. It's still in the shed somewhere ...
I must admit, I was rather taken aback when I recently started getting computer peripherals with built-in magnets to attach them to your computer case or laptop (with an extra plate to stick to the laptop, which presumably doesn't have a metal case, after all). A Wi-Fi/Bluetooth antenna that came with the motherboard, and a couple of SD card readers, are what I have so far with these magnets in them. After some hesitation, I figured they probably knew well enough (especially the motherboard/antenna one, a well-known name, not some fly-by-night knockoff from China that might throw anything at your computer case and see what sticks), and went ahead with it. I was somewhat comforted by having switched all my important drives to SSDs by then, and figuring that they couldn't really do much to those.
My son managed to trash his harddrive on his old macbook with a magnet attached to the case - don't know how long it took, but by the time he asked for my help, the disk wouldn't format cleanly. Fortunately not only are harddisks inexpensive, but apple makes recovering rather easy.
Many years ago, one of our customers needed a software upgrade, that was on QIC (too big for floppies) But their security insisted on running the QIC through the airport style xray tunnel thing - cue corrupted data. On the third trip out to them with yet another freshly minted QIC image, I'd got the bosses involved and I was allowed through with the QIC unscanned and unharmed.
Again, I would suggest looking for another reason to explain the disk not working. If it were magnetic damage, a low-level format would restore the disk to full use again, unless it had a servo surface which was damaged.
Please note that often what is called "format" on many OS's simply lays down the required filesystem constructs on the disk. A full low-level format will re-write the entire disk, possibly with the synchronisation and block and track numbering information. It is possible to find utilities to do this on a normal PC, but they are often difficult to find.
For disks with a servo surface (that contains the track and sector positioning information on one dedicated surface of one of the disk platters, away from the data tracks), it is normally not possible to completely format the disk, and if the servo information is damaged, the disk is toast unless sent somewhere with the the required equipment.
You've just caused my brain to remember that back in the DOS days, and probably with MFM / RLL drives, you could run up the debug command and execute a low level formatting command from the drive's own ROM. I have the address C800 in my head, but $deity knows if that's relevant!
I'll be damned if I can remember my own phone number these days ...
Works with 8-bit WD controllers (and clones), and most (not all!) WD or Seagate ST-506 type drives (and clones). What it does is run a low-level format utility that is built into the drive controller. 16-bit controllers brought us disk based low level format tools. Note that the Seagate ST-01 and -02 drive controllers were actually made by Western Digital.
Other addresses that might work are G=CA00:5, G=CC00:5 or G=CE00:5 ... check the jumpers on your particular card. If no pins are selected, they usually default to C800:5
This info is long out of date, and only useful to folks who are restoring old kit. You should not attempt it unless you know exactly what you are doing. I have seen this brick a couple of Maxtor 80 Meg IDE drive (no idea why), so don't just run it blindly. The results of running the command blindly on random hardware are undefined, and apt to do anything.
This post should give you more than enough info to DDG for more. Please educate yourself before ignorantly jumping in and breaking old kit needlessly. Ta.
All disclaimers aside, I suspect modern drives will just ignore it.
When I was at university there were a number of cases where tapes used by the mainframe (Unicac 1100) had become corrupted. Everything they could think of had been checked, but all came out negative; The problem persisted. After a number of weeks a pattern started emerging: it seemed that corruption occured over week-ends.
Interrogating staff and students did not yield any result either. Somebody (the professor who regaled the tale did not mention who) then decided to surreptituosly monitor the computer room, as well as the route along which tapes were transported from the computer room to the storage area, to see if he could catch the culprit red-handed. It took a number of weeks, but he finally got his man - or rather woman.
It turned out that the tapes used by students were kept in a large storage room accessible to everyone, since it was not valuable (in the sense tha the financial tapes were). These tapes were stored in wooden racks bolted to one wall, with the first shelf being about ten to fifteen centimetres above the floor, with three shelves above it. Regularly used tapes were stored on the middle two shelves (for easy access), whilst seldom-used tapes were on the bottom shelve and tapes that were deemed to be never used, plus new tapes, were on the top shelf.
On the particular day the culprit was caught, the Observer noticed the cleaning lady coming along, polishing the floors with a massive polisher (something like this ).
The shelf was just high enough off the floor to allow the polisher to get real up close and personal to the front of the tapes (being stored like a horizontal stack of coins). Those were noisy buggers; my mom had a Columbus like that.
Secondly (I think I have told the tale here before, but here is a summary): one of my colleagues told us a story about a server in a remote site (about 300 km away) that had suddenly started failing, almost to the minute, at the same time of day. Calls to the branch did not reveal any reason why it should shut down (no power failures or surges, nor anyone unplugging the server to plug in a vacuum cleaner or whatever). Eventually one of the techies were sent off on a nice Friday drive to observe the phenomenon first-hand.
The first thing he noticed, was that the server was not in the cubicle that served as a server room any more, but resided on a desk in front of a window. I cannot remember why it was moved, but it was probably because they were upgrading the cubicle to (or maybe creating) a proper server room, and that was the only available space for it to reside in the mean time.
The second thing that he noticed as the magic hour slowly approached, was that the sun had started to shine on the side of the server, the window being west-facing. And right on cue, after about an hour of being baked, the server dutifully shut down because it suffered thermal stress (the sun in Limpopo province in high summer can be brutal).
(Icon for the heat of the sun, obviously)
@Kobus Botes
Concerning your second anecdote here's a C&P of a similar post I wrote about 5 years ago.
Heard of a similar story concerning a mainframe (this was back in the 60-70's) that would crash fairly regularly during summer in the afternoon.
At first it was thought the cause was a defective aircon installation but checks and sensors said everything was okay.
Turned out that when the sun made its daily stroll across the sky, the computer room had this one particular window which would, in the afternoon, let the sun shine directly on the glass lid of the disk unit housing the system pack.
I cured a glitchy CRT (the picture wobbled at about 50Hz) by nipping into the lab next door (after hours) and moving a lab waterbath (which have a big stirrer inside driven by -obviously- an electric motor) from the adjoining wall to other wall.
(Note: after hours because the inhabitants of the lab had refused to move the bloody thing when asked...)
Next day -
Did you move that waterbath?
What waterbath?
I was in a department store (remember those?) to troubleshoot the network connection to a POS terminal. Connected my laptop to the drop to run ping tests, etc, Space on the cashwrap was limited. Set the lappy on top of things. Went off to check at the other end of the cable in the IDF. Came back to find the laptop blue-screened. Turns out that one of the things I'd set it on was the magnetic device for removing antitheft tags from clothing.
The drive was an ex-drive; it could not be reformatted.
If the device was one of those that burns out the RFID tags, then I would believe that.
Most RFID tags are not self powered, and pick up their power from the reader via magnetic induction. This requires a localised, magnetic field, which is picked up by an antenna in the tag, and powers the chip.
When someone waves the tag over the tag immobiliser, it actually overloads the tag by having a much stronger magnetic field than that required to read the tag, which blows a fuse in it, rendering it inactive.
And yes, it if damaged the embedded servo locator information, it wouldn't format.
Reminds me of the time when I was at a Macworld trade show and strolled past the Prodigy booth--at the time, the only consumer service worse than AOL. I was amused to see them handing out Prodigy floppies (standard fare in those bygone days)... along with Prodigy fridge magnets! As I watched the swag drop into people's goodie bags, I wondered whether any of them would be able to sign on when they got home.
This isn't about fridge magnets or corrupted drives, but it is about magnetic fields. Had a user with a CRT that kept getting 60Hz interference. He had to use the computer during the day so I had to wait until after hours to play with it. Took three late nights to fix.
Looked for nearby fans or space heaters. Nothing. Swapped out the CRT. No change. On the third night I was sitting at his desk contemplating the possibilities when I remembered an important detail: one end of his desk was pressed against the wall dividing his (shared) office from the hallway, the CRT was at that end of the desk, and on the other side of the wall was an access panel. That panel accessed the circuit breaker panel that fed power to the entire factory floor. There were about 100 gazillion amps of 60Hz AC running through ginormous wires mere inches away from the CRT. It wasn't obvious because from his side it was just a blank wall.
No wonder the poor thing was upset.
I gently moved some of his tchatchkes out of the way, moved the CRT to the other end of the desk, and voila! the interference disappeared.
Left the CRT there and a note. He was happy with the solution and simply re-arranged his desk to accommodate.
(Two things will be obvious by now: 1) this was in the USA and 2) this was in the 1990s.)
In the late 80s, we had a customer with a machine which regularly got its drive corrupted.
We were regular visitors (they spent quite a bit with us), so we would be presented with the machine, on which we would run the low-level (factory) format. Remember MFM? Reinstall their standard stuff and hand it back, All would be well for another few weeks,
Then came the visit when the problem had only just happened. This time we collected the box from its normal hiding place rather than it being ready for attention.
Sitting on top of it was an old-fashioned telephone. The sort with a loud bell, operated with a hefty magnetic coil.
We nipped to the shop while the format was going on, and spent a tenner on a new handset with an electronic squawker.
Happy customer!
After reading so many "cannot be" comments here I have to dig out my smart-ass-physics why they can erase data more efficiently compared to Neodyms...
Most fridge magnets don't have one magnetic field. They have an alternating magnet field, alternating every few millimeters. If you've ever seen how they are made: You take strong round rare earth magnets, put them alternating in a row in SN-NS-SN-NS-etc orientation. The fridge magnet material base is then, while being hot, contacted with that magnet collection. Thus creating an alternating magnetization which changes its direction every few millimeters.
This alternating field expands to the outside, and any fast rotating object will be facing that field between 30 and 167 times each second, passing through that field which alternates 10+ times withing a VERY short time, i.e. frequency above 1000 Hz, in some cases above 10000 Hz. Take some more or larger of them and you easily have 100+ of such alternating fields, with every rotation.
Taken that into consideration it is more than realistic for those to demagnetize a disk easily, even when enclosed in metal.
See https://en.wikipedia.org/wiki/Refrigerator_magnet and https://en.wikipedia.org/wiki/Halbach_array ...
If you take the normal usual Neodym magnet, which has only one North and one South you have way less strong than you imagine compared to an "weak" magnetic field which alternates every few millimeters. You would have to spin that singe magnet with > 1000 rotations rectangular to their magnetic orientation ax to have an actual comparison. But be aware: Electricity induced by magnets works.
Even more: The strong magnets in those HDDs themselves are oriented and enclosed to create a closed magnetic fields which expands near NIL outside of its package.
Actually I first learned that from the German "Die Sendung mit der Maus" before the year 2000. A Children show presenting science among cartoons. Actual science, correctly told down into the detail.
Have a nice weekend!
The problem here is sheet steel (or any other material with high magnetic permeability) are good magnetic shields because the field lines will preferential choose the steel case over the air around it.
Lots of flux reversals might be good for sticking them to steel but if the field doesn't penetrate strongly it doesn't much matter how many flux reversals there are, for anything the other side of the shield.
You mean a Halbach array to give it the correct name.
IT can ideally double the field strength on one side if done correctly - which isn't going to be a huge increase in absolute terms for a frdige magnet...
The thing about there being many reversals means nothing if the flux change is less than the coercivity of the magnetic media. A typical platter has a coercivity - even for the older drives of at least 2000Ga - whats the flux density needed to write that then with the very small sized domains on a drive platter? My numbers tell me about 0.3T - still think a 5mT magnet will manage it?
https://cobolhacker3.wordpress.com/2006/10/28/is-it-possible-to-erase-a-hard-drive-with-magnets/
Quite a long time ago... The customer had an analogue voice recording machine. This used large reels of tape that lasted about 24 hours and they kept them for about a month before reusing the tape. The Voice recorder had no erase function so the erasure was done on a degaussing machine. This creates an magnetic field around the tape and randomised the magnetism of the tape particles. The problem arose when they moved this and put it next to the disk drive units...
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