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Cringely's Shameless Self-Promotion
wild_berry writes "The latest edition of Bob Cringely's column at pbs.org, entitled Shameless Self-Promotion: Bob's Disk Drive is up. He's talking about replacing the glass or metal platters in present hard disk drives with foil platters in order to save energy." From the article: "The materials cost more but we use so much less of it (the disk is so incredibly thin) that the total material cost is substantially less. This 'floppy' material has the same kind of magnetic coatings used on standard disk drives and our drives live on the same technology growth curve as those others. The way we obtain greater storage density is simply by putting more platters in a drive (say 12-15 instead of 4-5 in an enterprise 3.5-inch drive) because they are much thinner and can be stacked closer together. The only parts of the drive that are significantly different are the platters and the heads and the heads vary only in having an extra slot."
The only time you'd see a difference in energy consumption would be during spin-up. Not worth optimizing such a rare case (except possibly in a laptop drive where it does happen a lot and would contribute to battery life.)
What about gyroscopic forces? turn the drive 90 degrees and teh spinning disks will want to turn a different way. Light weight helps reduce this, but it sstill must be strong enough not to shear itself off the spindle....
You are in a maze of twisted little posts, all alike.
Speed control of the rotating disk is going to be harder if the disk has less mass. You basically loose a nice dampener that you had in the system.
The only real power savings would come during spin-up. Once the disk is spinning, there's no additional power used to rotate a heavy vs. a light flywheel. (Well, a little bit because of increased bearing friction, but it's probably negligible.)
Finally, if you lighten up the parts in a hard drive, most companies are just going to use the energy savings to drive the parts FASTER.
IANADDEBIAAME*
*I Am Not A Disk Drive Engineer But I Am A Mechanical Engineer
W..w..W - Willy Waterloo washes Warren Wiggins who is washing Waldo Woo.
The real savings comes from the fact that the coating/finishing of the platters can be done on a big roll of foil and the platters can then be just stamped out. Standard platters must be finished individually.
I don't read your sig. Why are you reading mine?
Assuming the disks were very smooth and the internal atmosphere of the drive is gas-only (no dust - a safe assumption)
From the article: "the nature of our flying heads is such that dust is sucked away from the head-disk interface, meaning the drives do not have to be assembled in a clean room.". So presumably any dust that does drift onto the platter simply doesn't cause enough of a turbulance problem.
In particular, I'd like to see evidence for the following claims:
I'd sure like to see the assumptions and numbers underlying that equation. Gee, Cringe, which do you think costs more: The raw platters themselves, or the read/write heads? I would say the latter. So you're going to drop the costs of hard drives by doubling the most expensive component? Huh? Sorry, I'm not buying this at all. You don't think a non-cleanroom enclosure is going to result in data loss on the platters themselves? Even if you're not getting particles during the read/write phase itself, you're getting them on the platter. I'm not buying the logic here. Sorry, I'm not buying this at all. Until the advent of true Drexlarian nanotechnology, I doubt you're going to see a mechanical action (you still have to move the eread/write heads) beat an eletronic one (reading from Flash).I'm not saying that the technology Cringely talks about is impossible, I'm saying: A.) There seem to be a lot of unwarrented assumptions underlying his logic, and B.) Implementation always has unforeseen hurldes and obstacles that will make these drives seem like far less of a slam-dunk vs. current technology (or more specifically, where regular drive technology will be 18 months from now) than it appears.
Finally, once it is ready, I'd like to see real-world tests for speed/electrical consumption metrics with existing technology. There might indeed be some savings, but I seriously doubt they are as dramatic as Cringely claims.
Crow T. Trollbot
Turbulence isn't created by dust, it's a feature of the non-linearity of the Navier Stokes equations.
The arm holding the read/write head sits in the middle of what would otherwise be a nicely rotating flow between the platters. The Reynolds number for flow between platters in a disk drive is going to be something like 30 m/s * 0.001 m / 2E-5 m^2/s = 1500 >> 1, so vortices will be shed off the back of the arm. Which basically means turbulence.
Incidentally, this is currently one of the limits to increasing disk drive performance per watt. The arm also creates drag, which you'd like to minimise. To do that, you make the arm as thin as possible. However, the thinner you make it, the less stiff it is. Too thin and it will deform too much because of the vortex shedding and get too close to the platters.
The disk is very floppy. The metal center is the only rigid part. The floppy plastic of which the disk is composed does not flop because it is too small, measuring only 1 3/16 of an inch from the metal hub.
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I think the frictional losses in disk drives are significant. Look at how much power is used by drives -- that's not the electronics, and I don't think the seek arm uses that much because it is so light. But I have never seen an actual breakdown of seek arm vs spin motor. I do know that the spin motors suck up a lot of power. There have been advances in bearings, but aero drag can't be reduced.
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