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Establishing the Maximum Speed of a CD-ROM Drive
UnknownSoldier writes "Ever wondered how fast CD-ROM drives can spin their CDs before the CD will self destruct due to centrifugal force? This person was too, and has his results. (So much for those 100x drives)."
The google cache for this page is here
32x might be exxagerating a little, but I know my 50x sounds like a jet engine taking off when it spins up.
Future drives will have to take advantage of technologies like TrueX to be tolerable.
Then again, how fast do I really need my CD-ROM to be? I mean, I only use my CD-ROM to 1) reinstall the system and 2) to play music. A 32x CD-ROM is plenty fast to accomplish both of these tasks.
The point of this experiment wasn't to push technology but to do something silly to wow your geek friends. (Then again, I didn't read the link since it was Slashdotted after a measely 6 posts).
What i'm waiting for..
are scratch-resistant CD's. or CD's you can pull the outer layer off of to reveal a new shiny surface. I treat my burnt cd's like shite, so its my own fault.. but still.
what isn't my fault is old cd's who's upper reflective layer begins to flake off.. cheap sons of bitches made in 1997 just arent sufficent. I lost my entire backup of por..err, my 600mb hard disk.
You probably already know this, but just for the record -- unless you have a defective CD drive, it shouldn't ever try to spin an audio disc up to full speed unless you're doing digital audio extraction. If you're merely listening to your CD, it will spin at 1X, just like any standard CD audio player.
Kenwood made a drive that does this. It spins at around 10x and reads at 72x. Unfortunately, they have discontinued it.
Donate background CPU time to fight cancer.
This one has no broken images.
What's the point? CD's are fast enough. I could get by with a 2X CD ROM, all I have to do is wait longer for the data!
Okay, sorry about that. I just wanted to do the obligatory "There's no practical value with this information" post so that I could get a +1 Informative.
"Derp de derp."
I would bet that it's cheaper and more practical to shrink the bits. This seems to have worked well for DVD.
Donate background CPU time to fight cancer.
Most (all?) CD-ROM drives over 32X already use multiple lasers to read multiple tracks at once. They usually say "multi-read" on the boxes if they use this technology. Zen research (http://www.zenresearch.com/) invented this technique, and holds patents relating to it.
Afreey and Infineon already have a 100x (TrueX) CD-Rom drive (25x DVD)", it came out in 2001...
This is the future (but who cares, we'll go solid state before it gets popular).
Imperium et libertas
Autocracy and freedom
Background
The Audio CD Standard was set sometime back in the 70's. Then, it was decided that the record should rotate with different speeds, depending on where on the record the data was read, to get a constant data transfer rate. The method is named CLV (Constant Linear Velocity), or constant transfer rate. The transfer rate of an audio CD is a mere 176 kB/s, and to reach this rate the record only has to spin with 530 rpm when reading the innermost track, and 200 rpm for the outer track.
CAV is for Whimps
To be able to publish ever increasing spin ratios, many manufacturers have resorted to CAV (Constant Angular Velocity), a method whereby the record is not rotated faster when reading inner tracks. Thus they can specify impressive spin ratios for outer tracks and sell more, but in reality the spin ratio for the inner tracks is only 37.7% of this value.
CLV is for the Tough Boys
A 64x drive using CLV would have to rotate the disc with 33,920 rpm when reading an inner track, exposing the hub of the disk to a tangential force of some 45 N/mm2. A point on the periphery of the disc will be moving with 213 metres per second, slightly more than half the speed of sound. Can the disc take that?
The answer is no. A powerful no.
At about 52x, i.e. 27,500 rpm, most manufacturer's CDs blew up in a rain of plastic particles, leaving their marks on the premises. The result was a pile of shimmering plastic chips.
He also tried Kevlar reinforcement
In our efforts of reaching ever increasing speeds, we tried to reinforce a disc with Kevlar wires. [...] It turned out our motor didn't have enough power to spin up the disc enough to explode it in one try, because the Kevlar wires consumed several hundred watts of motor power for aerobreaking. [photo] After an extended period of time (about 20 seconds) at close to 28,000 rpm, the disc blew up with a loud bang anyway, with the wires remaining on the hub, as shown in the picture. It can be clearly seen that the wires remains pointing radially from the hub. The Kevlar wires had been stretched radially and performed as intended. What made the disc explode, was the creepage of the plastic material, i.e. its stretching over time, subjected to the high g forces.
"It is a greater offense to steal men's labor, than their clothes"
well this is not entirely true... although it is true that a cdrom needs time to position the laser lens over a sector that is not very much of the time... your thinking too much like hard drives... in a hard drive you get fragmentation which means the head must spin all over the place gathering all the data into one file... there is no fragmentation of cdroms as they are used more and more... so a hard drive uses a combination of sequentail AND random IO's where as a cdrom uses mostly seqential IO... and manufacturer's usually measure their cdrom by the spinm spead which is not a true test of speed... a cd can spin real fast but it wont read that fast sometimes and in fact the only thing that helps is positioning the lens... so what you really need is a high quality drive... dont skimp on the drive... get a name brand drive... it really does help... personally i like tishiba cause they make a fairly good cd-rw/dvd drive that is cheap but when looking around try to find out some REAL info about the cdrom not just some post X speed...
unzip; strip; touch; finger; mount; fsck; more; yes; unmount; sleep
It's simple. They spin them more slowly than that and then lie about the specs.
-- Remember that we live in a world where all the really big decisions are made by people with short attention spans.
Sorry to be a physics geek here, but there's no such thing as "centrifugal" force, unless you're talking about the force caused by a centrifuge dropped from a height.
There IS "centripetal" force, that refers to the force on an object travelling in a circle, which pushes outward from the axis of said circle on an object while it's travelling about the radius. Say you're spinning a ball on a string around over your head. Your work is translated into acceleration around the axis of the circle as the ball spins around your head, but the force is perpendicular to the path of the ball at any one moment, radiating from the axis. This is proven visually by noting that as you put in more work, spinning the ball faster, the angle from vertical of the string the ball's attached to increases toward 90 degrees. See? Force pushing outward, ball moving in circle. When the string is released though (or the CD breaks up) the ball moves in a straight line matching that along which it was travelling at the moment of release -- momentum then is in action.
To repeat, no centrifugal force. For all our computer learnin', it's surprising that so few paid attention in physics 101.
The only tool you've got against psychosis is experience.
http://www.qedata.se/e_js_n-cdrom.htm
Heh, I figured I'd get either funny or off-topic, wasn't expecting to get 'informative' points.
:) *Watches his Karma roller-coaster*
I honestly meant that as a joke. Seems like every time an article like this shows up on Slashdot, there's always somebody ready to say "whats the point?"
Oh well.
"Derp de derp."
Last time I broke a CD, I formed the opinion that a CD is a single piece of plastic with a single piece of foil. On the other side of the foil is the label. There is no foil "sandwich".
I think the man is making a smart-aleck comment here, AND pointing out a flaw in the article(? writeup? the site was dead before I got there) There is NO SUCH THING as centrifugal force, it is really a combination of angular and centripetal acceleration that causes the sensation of centrifugal force.
I teach Physics 100A. The best way to think about Centripital "force" is: it is whatever force holds the object in circular motion. (Thus it must be directed towards the center of the circular motion). For example, the earth is held in a (nearly) circular orbit around the sun by gravity. Your car can go around a curve, and locally travel in "circular" motion and it is held in the turn by friction (unless the turn is "banked" - you know, like highway turns, then gravity assists you, also).
What is called "centrifugal" force does not exist. What is most commonly cited as a "centrifugal" force is a force which pushes things out from the center of circular motion. In fact, there is no magical force pushing things away from the center of circular motion. What you feel is called inertia: the tendancy for objects to go in a straight line unless acted on by an outside force. This is not a force, it is Newton's first law.
The expression which is *not* a force is mass times speed squared divided by radius. It is a mass times acceleration, which belongs on the "right" hand side of Newton's second law, which says: the sum of all forces equals mass times acceleration. There is an expression for centripital acceleration because by stating the object is traveling in circular motion, you are saying something about what acceleration it is experiencing: namely that the acceleration is directed inward and has magnitude equal to speed squared divided by radius. (What is called "uniform" circular motion adds an additional requirement: that the speed does not change. (The velocity is a vector, so it sure does change in circular motion!) In the case of uniform circular motion, the only acceleration is centripital (center seeking), whereas in general you can also have tangential acceleration as well which changes the speed). There are magnetic, electric, and frictional forces. There are no equations for magnetic, electric, and frictional accelerations. The live on the left hand side of Newton's second law. Each can cause circular motion, and thus can be what is refered to as a "centripital" force. In general, there may be many forces acting to hold an object in circular motion.
By the way, floW is actually right about Newton's laws not holding in accelerating frames of reference. However, we don't invoke centrifugal forces to deal with this "problem". Perhaps the author was refering to the coriolis force, which *is* a fictional force.
We use the coriolis force because the effect is rather small on Earth and it is more intuitive to view Earth as a non-accelerating system, rather than one which is rotating. You may have hear about the coriolis force in physics 101 but you likely did not compute it. To do so you need the vector product (or cross product) which generally is not used in into physics books like Giancoli, Serway or Haladay and Resnik. The coriolis force effects: storm systems, water swirling down a drain, the Foucault pendulum (in fact any pendulum, but the giant pendulums in museums which knock over dominoes or trace out lines in sand are designed with coriolis in mind and called "Foucalut's" - it has to do with velocity that the pendulum achieves), and actually is used in firing Naval guns. See, for example:
some physics stuff
There is quite a bit of confusion as to what the force is that is holding the disc in circular motion. Most forces cited are actually what will cause the disc to either speed up, or slow down. The force holding the disc in circular motion is actually the atomic forces. This is why the disc does not fly apart (each part traveling in a staight line).
By the way, I actually searched for a few minuets trying to find a decent explanation of all this on the web, but most have mistakes. I am sorry to say the only way to really learn this seems to be to get a published book like Giancoli, Serway or Haladay's books (all titled Physics or something like that).
This is actually a rather delicate issue which I don't think most physics 100 students *ever* grasp. In fact, even after careful re-reading, I may have made mistakes. Heck, I get paid to explain this stuff to people, (which is a great joy) so I hope someone gets something out of this, even if it is inexact.
Gregory G. Wood
a war on terrorism? How can we end a war on a method?
Actually, CDs are made up of a metallic aluminum (or gold) layer sandwiched between a tough polycarbonate layer and a very thin lacquer layer. The label is printed on top of this layer of lacquer, which is much more sensitive to damage than the underside.
Reading multiple times at the same go helps to multiply the reading spead nicely, here's a review of their product:
:/ It would have been nice to get a version with adjustable speed from 1x to 52x with their multibeam technology.
kenwood 72x drive
But it seems that Kenwood has discontinued the product
I work in a lab where we are testing CD drives at extreme speeds. I think the original article - although had some good points - is rubbish. It depends on which material CDs are made. It is possible to manufacture CDs using aluminum - with these discs one can have a CDROM drive which operates at 4000x.
I have a Kenwood 72x True-X drive. Kinda wish I hadn't purchased it. It reads all my CD-R's just fine, but you're right, it won't read CD-RW's for shit. On top of that I have to disable DMA in order to play any Safedisc protected games. And I really can't notice any speed increase over my Toshiba DVD drive (not sure what the read speed is on this one).
The coriolis force _does_ affect the water going down the drain. But it does so much much weaker than the inertia kept from flowing in. It's real, it's just so small that it's not the reason for the observed rotation.
It's called an "acoustic optical modulator", my old company uses them all the time in their laser photographic printers.
We modulate a laser beam on the order of 14 million times a second, actually a lot more than that. Check out www.cymbolic.com (LightJet / PlateJet products).
MadCow.
I used to have a sig, but I set it free and it never came back.
Lithium Niobate Modulaters go at 20 Ghz ( I have one sitting in front of me in a box).
http://www.eospace.com/
Hell they even have a 40 Gb/s, but it isn't that good.
Anyway if you want to redirect the light beam you can use a lithium niobate polarization controller and have polarization dependent componets at the output that only let certain states of light through (and attenuate the rest) and thus you are redirecting the beam down a different waveguide in the ps range.
I am sure there are easier ways. But it is saturday morning....