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Clear Hard Drive Mods
Baloo Ursidae writes "In the spirit of the case window kit and the clear PC case, there are people who have made hard drive windows, and apparently they're not alone."
That ladies and gentlemen, takes balls.
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You're creating a Farraday Cage, where any energy that goes out hits a piece of metal, gets absorbed, then goes to ground and out. The metal tabs along the edges prevent any waves that are in the same phase as the opening from leaving. So by putting metal tabs along a non-conductive material will help, but not much. The waves will still pass right through the material and out.
I used to do FCC and UL testing of PCs, so ran into this often.
As a former hard drive engineer for IBM, I can aboslutely tell you that if you do this mod your hard drive will not last long.
The case is nearly sealed-- the only opening is for pressure equalization and is protected by a pretty advanced catacomb filter. Drives are assembled in clean rooms to minimze the internal particle count after manufacture. Remember that the distance between the (moving) head and the (spinning) media is measured in nanometers!
Why does a hard drive stop working when it takes a shock, sometimes not when the shock happens but a few hours/days/weeks later? It's becuase the heads slapped into the media, chipping off some of the magnetic material. That doesn't immediately kill it-- the disk automatically notices that it can't write those bits anymore, and reassigns them to one of the spare areas. It's the little bits of magnetic material floating around the drive that kill it. Eventually, they find their way to one of the heads and block it from reading/writing. Or, more spectacularly (and more rare) if the debris is big enough, it will wedge in between the head and the media and score the substrate (aluminum or glass), which sounds a little bit like a turbine exploding.
Hard drives are incredibly complex and sensitive devices. Unless you also think it would be cool to crack open your processor case and put a little window on it-- don't do your hard drive. Now, if you have a hard drive you don't need, you can add the window to make it look cool, but don't expect it to work. Also, it's unlikely the arms will move much, so just expect to see the platters spinning.
Yes, modding your hard drive will introduce impurities into it. Yes, you will void the warranty, yes, you will offend the Gods and generate additional RF.
But, it's a mod that you do because you want to, damn the consequences. It's done....for fun, for the hell of it, because you can, because it's there.
Chill out, lay off the "Yeah buts" and applaud the chutzpah that it takes to actually do this....but do not try it with ANYTHING mission critical!
.01" ? ROFL
I am a firmware engineer for Maxtor...
The heads on our drives, and everyone else's in IDE land are currently flying at some fraction of a micron, if they aren't burnished already (sliding through the layer of lubrication on the surface of the platter).
Put to scale, the head of a disk drive is like a 747 jumbo jet flying at mach 4 at an altitude of 1/4" over the rocky mountains.
A single particle of dust inside the drive is HUGE, and can easily cause catastrophic data failure. If the head touches the media at all, you can basically forget the adjacent 10-20 tracks on each side, which on a modern drive is roughly 15 megabytes at least. If the strike happened while the drive was seeking, you get a radial scratch which can be destructive to a much larger area of the drive.
Bottom line: don't do it, no matter how cool you think you might be. They're fragile enough as it is.
More data, damnit!
Well given what you said I don't think you did EMC testing for the FCC and UL. Your description of how a _Faraday_ cage works is stunningly wrong.
A good conductor reflects incident waves very very efficiently. Very little power is absorbed by the metal itself. If you surround a region with metal, all incident radiation from outside the box is scattered and does not enter the box.
If you want add a transparent window to the box, all you have to do is integrate a metal wire mesh fine enough so that the gaps are much smaller than the wavelengths of the frequencies you want to filter out. So, to filter out all frequencies below 2.4 GHz (lambda = 12.5 cm), you want a mesh much finer spacing on the order of 1.25mm - 1.25cm. (How do you think your microwave oven window works?)
Only if you are talking very low frequencies, would even talking about "goes to ground and out" have any meaningful content (like 60Hz which is essentially the same as DC from any electromagnetics theory standpoing unless your devices are the size of the continential U.S.)
Kevin
P.S. By the way, my Ph.D. background is electromagnetics and I had an office inside a Faraday cage at a former employer.
OK, quick quiz.
What gets written to your swap? Pages from your memory!
Pages get corrupt, swapped back in... instant swiss cheese computer.
I'd say it's a lot more safe to use one of these drives for unimportant storage, than something critical like swap. You are basically adding bad RAM to you system in essence.
I've had enough abrasive sigs. Kittens are cute and fuzzy.
It is 747 in size, not in mass.
A GMR head is visible to the naked eye (tiny tiny black speck on the end of the actuator) The actual read element is not visible to the eye.
It is basically shaped like a huge surfboard, where there is a tiny element on the back end of the surfboard that does the actual reading / writing.
There are 20-60 data tracks at present in modern drives within the thickness of a piece of paper. That is the required lateral accuracy.
Vertical accuracy is assisted by the use of an "air bearing". This is common to all drives to my knowledge. Basically, our head flies along similar to the way a low altitude helicopter flies upon a cushion of its own prop wash. The heads are designed like wings, and they channel a tiny bit of air underneath the head. If the head drops lower due to a bump in the media, the air pressure increases, forcing the head to resist the change to a lower altitude. Similarly, no cushion of air is created at high altitude, so this causes the head to settle down on the platter.
When you compare the size of the head to its distance from the ground, a 747 at 1/4" was accurate as of 18 months ago. Now it is even lower.
As to the rocky mountains, ok, sure, the bumps might not be quite that big, but they're at least the Appalachians. On the fractional micron scale that everything works at, there's no practical way to flatten the media that perfectly. Besides, if the media were perfectly smooth it would create too much surface tension and the head would stick to it (called "stiction"), so actually parts of the media are intentionally textured to reduce the amount of surface that might actually touch the head at any given time.
As to your F16 comment, just how maneuverable do you think the head of a drive is? We can't steer our heads onto a track, we can only recognize that we missed the track and need to adjust.
Perhaps I should have said we were an oil tanker flying mach 4 at 1/2" of altitude down an olympic slalom course.
Hell I am amazed the things even work, knowing what I know about them.
More data, damnit!
I am a test engineer for Maxtor in advanced recording technology. It's actually quite amazing how robust these things are given the dimensions we're working at, it can actually be quite difficult to get a head to crash. Now I am in no way condoning this mod but this issue of "dust" needs a little clarification. It is virtually impossible for dust to get between the head and the disk. Imagine the 747 flying 1/4" above the ground analogy. On that scale a dust particle is about the size of house. The head will simply knock any dust particles out of its way. Even smoke particles are huge compared to the sub-micro inch spacing between the head and disk. Having said that however there is a contamination issue but from materials much smaller than dust. Molecular out-gassing is a big problem in drives and every material inside the drive is tested and appropriate filters are built into the drive to trap these gasses. Putting a big slab of plexiglass in the drive enviroment simply was not accounted for when designing those scrubbers. There is also the issue of humidity and the resulting corrosion. What REALLY scares me about this procedure is that Saran Wrap casually draped over the drive while the cover is being hacked up. What kills heads these days is static charge. That Saran Wrap is one of the most easily charged materials in the known universe, and it only takes a few volts to kill a head. And then, the window itself is plexiglas, another material that charges up just by looking at it. So, while I might take exception to the issue of dust, I'm in total agreement that this mod is simply a BAD IDEA. If you do it, do it for show only, do not put any data on it that you can't afford to lose at any moment and without warning. Failure may not be immediate but will almost certainly be instantaneous and catastrophic when it does occur. Steve
Yes, two identical IMB Travelstars. Same size, same model number. One ticked and burped on startup, the other had a password lock on the platter (which the controller knew about, and so wouldn't play ball). They were bought as seen on eBay for next to nothing, so I didn't expect them to work, and really had very little to lose.
Isn't the 75GXP the model that a lot of people had problems with? And the problem was with the physical platters breaking down? I'm not sure what you'd gain by moving the platters to a new drive, unless you know that it's the head, arm or motor that's screwed. In the first instance, you could try the controller from an identical drive. Swapping platters really is the last resort of the desparate, I think. ;-)
If you were blocking sigs, you wouldn't have to read this.