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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."
Ideally, the disks would be spinning so quickly that the outward force would keep them almost perfectly flat. Assuming the disks were very smooth and the internal atmosphere of the drive is gas-only (no dust - a safe assumption) there would hopefully be very little turbulence within the drive to cause fluctuations in the flatness of each platter.
In my lab we coat floppy materials (like plastic) in a spin coater at several thousand RPM. At that speed the disk may aswell be rigid.
At the UIUC Reflections|Projects ACM conference. It was actually a fairly interesting talk (http://www.acm.uiuc.edu/conference/2006/webcast.p hp) about the same topic, maybe a little more in-depth than the article. At least more pretty pictures than the article.
Slashdot Patriotism: We Support our Dupes!
According to TFA, they'd use extremely strong materials like Stainless Steel or Titanium to ensure the rigidity of the disks. They claim that this would be just as shock resistant as a Flash drive, but with faster seek time. (i.e. the lighter weight would mean less inertia to fight against)
Javascript + Nintendo DSi = DSiCade
Cringley must be old enough to remember Bernoulli disks. (They used a plastic film but same concept applies.)
Uhm... That's NOT quite true... Cut the power off, the disc eventually stops spinning because of friction, etc.
You need to supply a constant input of angular momentum to keep the discs spinning. Spinning a
smaller mass will ALWAYS mean a lower power input, from start to finish and everything in betweeen.
I am not merely a "consumer" or a "taxpayer". I am a Citizen of the State of Texas
Actually, they have a thin metal version of this technology in a removable cartridge form
that's the size and thickness of a credit card with a smartcard contact point on it for
the crypto control on the disc. 100Mbytes to over 5Gbytes in a device allegedly more durable
than Flash (it's got the same vibration, etc. characteristics supposedly, but it's write
endurance vastly exceeds Flash right at the moment...)- in a credit card's space. What Bob
did was suggest that they apply the tech to fixed disc devices- and the article talks to the
potential results thereof.
I am not merely a "consumer" or a "taxpayer". I am a Citizen of the State of Texas
All hard drives do that. In fact, if you suddenly cut off a normal hard drives power, the momentum of the disk will keep it spinning long enough to maintain said cushion of air while the head returns to the parking position.
Slow Down, Cowboy! It's been 60 minutes since you last successfully posted a comment.
I don't follow your point. I said that my first concern would be that the technology would be prone to breakage. My next point, however, was that TFA is claiming that the disks would be more reliable than current disks. I said that it is a bold claim, and that I hope it works out for them.
How you got from there to "you should have read the whole article" is beyond me. I'm not going to quote every point they make just to say that they're claiming greater reliability.
Javascript + Nintendo DSi = DSiCade
The platters have (per platter) a much smaller edge, so they're going to get less friction from the air. Less friction means less heat AND less power required to keep the disk spinning at the same velocity. The area isn't that big compared to the surface of the disk, but I'd guess (assuming the heads were at the outer tracks of the disk) that the air near the spindle spins with the disks and probably causes very little if any friction, so the majority source of air friction is going to be the edge (where it moves air around the "interesting" interior shape of the enclosure).
In his talk I referenced above, he specifically stated that they were using smaller/lower power motors because they didn't need as much power as a conventional disk. Also remember that conventional disk motors may have to be "overspecced" to be able to spin the disks up to speed in a reasonable amount of time, and that may make them less efficient when they're just trying to maintain speed rather than spin up. You'd have to ask an EE on that one though, 'cuz I'm not. Just another stab that occurs to me for why it may cost a lot less power.
He also referenced making higher-RPM drives than current methods. I want to say 30k sticks in my head, but I'm not sure on that you'd have to watch the talk to verify my tylenol cold muddled memory.
Slashdot Patriotism: We Support our Dupes!
The article is admittedly short on specifics, but I imagine they'll be forthcoming, since he also mentioned that we'd actually be seeing the drives from numerous manufacturers next year.
If they managed to prove the tech to drive manufacturers, I'd imagine the dimensional stability of glass didn't trump the tech they're introducing.
"Murphy was an optimist" - O'Toole's commentary on Murphy's Law
Not sure who the multiple HDD vendors are that will be introducing it next year, but I'm sure they asked a lot of questions about that, too.
"Murphy was an optimist" - O'Toole's commentary on Murphy's Law
Not exactly true. Remember that the coefficient of friction is just a imensionless scalar value, it is not the actual force of friction. You need to multiply the coefficient of friction by the normal force between the two objects that are moving past each other. In this case we are talking about the mass of the flywheel acting upon its pivot point. I believe the relationship of friction to the mass of the flywheel is linear so a flywheel that is twice as massive as a ligher flywheel will take twice as much energy to maintain the same angular momentum.
And yes, it is actually a bit more complicated than this depending on how the flywheel is supported on its axis but the fact remains that the mass of the flywheel does have some bearing on the energy needed to maintain its angular momentum.
Sapere aude!
>The platters have (per platter) a much smaller edge, so they're going to get less friction from the air.
i f
Not failed physics... this is a flawed analysis.
There are a few different types of drag (I am an aerospace engineer). The relevant one in this case is caused by the surface of the platter, not the edge. Remember, the edge is really acting as if it were stationary - it's not moving the disc laterally thru the air, so the edge is irrelevant. Instead, the disk surface moving past the air drags some of the air with it - this is sometimes referred to as surface drag, or skin friction. No matter how smooth the surface is, moving it thru a "fluid" (such as air) causes shear in the fluid - the fluid closest to the surface is motionless, and the speed builds up as you move out away from the skin. This is called a "boundary layer". This layer can be smooth-flowing ("laminar flow") or rough (turbulent). Smoother skin means laminar flow. But there's STILL drag, no matter how smooth the surface.
Here's a good illustration: http://wright.nasa.gov/airplane/Images/boundlay.g
So making thinner disks and using more of them means MORE drag, not less.
Actually in this case, however, the motor can be sized DOWN, despite higher operating drag, because the largest power usage comes from spinning up the disc package - and a set of lighter disks will require less power to spin up. Very little power is actually used to keep it spinning, despite the drag.
--Brandon / Split Infinity Music
If I'm reading the article correctly, the claim seems to be that the lighter platters will save energy?
How?
With my primitive understanding of physics, the power required to keep something at constant velocity is basically the sum of the parasitic losses (in this case, aerodynamic and frictional losses). Changing the weight of the platter does not have much impact on energy consumption *except* for periods of acceleration (e.g. - the first couple of seconds during power-on).
Has my logic failed me here? How do the lighter platters save energy in a constant velocity system?
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