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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)."
Will the next computer snake oilish product be 'cd glue' to prevent you cds from falling apart, citing this paper? :)
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you could spin *both* the disc and the reading head (in opposite directions).
- 6 replies here and the site already is slashdotted.
Anyway, I think you can make cd drives that spin 4000x if you want, because it might be possible to put the cd in braces to hold it together, and/or to rotate the laser instead. Or how about using multiple lasers?
It's just like silicon transistors: There's always somebody saying there is a final physical limit we'll reach within the five years...
Often, we(they)'ll find a way around the limitation.
--- Hindsight is 20/20, but walking backwards is not the answer.
Contrary to popular belief, plastic doesn't last forever.
And since CD is made up of two layers of clear plastic, sandwitching a thin wafer of metal media inside, the more the CD is aged, the weaker the plastics of the CD become.
And so, the maximum spinning speed for a CD depends on how old the CD is.
I do have some pretty old CDs from the early 80's, and I will NOT put them in my 52X CDROM drive. Unless of course, I want to scrap bits and pieces out of my machine.
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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).
That is old technology, trying to mimic an LP and it needs to be changed!
Instead of spinning the disk, just have one laser suspended above the CD with a splitter that alters the direction of the beam, like maybe similar in concept to a cathode ray beam. Have the "read" sensor at the focal point of a parabolic mirror covering the top of the cdrom case and fire the laser at whatever angle it takes to hit position X. The beam will bounce off the pit and either scatter or reflect back up into the mirror striking the focal point, with seek times limited only by the speed of light! Forget 100X, if you did it this way you'd be looking at 100,000,000x speeds from CDs that don't even move an inch!
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Who would want a 100x drive? I think I've sustained permenant hearing loss from the whine of my 32x drive.
The biggest problem with these sort of drives is seek time. A modern drive can read the whole CD in under 2 minutes, but it will take a good fraction of a second to jump from one part of a drive to another. This doesn't improve alot no matter how fast you spin the CD.
A far better solution would be to build a CD with a 640 MB Cache, and have it just read the whole thing into RAM.
Given the price of RAM over the next few years, this sort of technology should available soon.
Alternatively, it could be written into the OS itself. The only problem with this could be with some copy protection systems perhaps.
Michael
There is no cryptographic solution to the problem where the intended receiver and the attacker are the same entity.
My next GPLed project will involve CD-ROMs spining at 99x, and sharks with frickin' laser beams attached to their heads.
--
Kenwood made a drive that does this. It spins at around 10x and reads at 72x. Unfortunately, they have discontinued it.
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This one has no broken images.
The spin rate seems like it is turning into a consumer numbers game, like CPU speed is/was doing for a while. People who don't know any better compare the raw CPU frequency rates.
It seems at the higher CD speed it takes too long spin the thing up to reading speed anyhow. If it did not need to spin so fast, then it may be able to get smaller chunks of information sooner.
Most don't seem to be able to read until full speed is reached. Why can't they read during the spin-up time also? Too hard to calculate?
Is there a way to set the speed of CD readers slower if one wants this? I have not seen any setting options, but each vendor may be different.
Table-ized A.I.
The slow seek time doesn't bother me nearly as much as the eternity it takes from the time you insert the CD in the drive until the time it is ready to send data. In fact, I'd probably be happy with an 8X drive if it had a < 1 second delay between hitting the close button and viewing the README file.
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).
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I don't know ... you don't happen to teach shop class and have only 7 fingers do you?
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Basically, you hold the CD still in a little bracket, and spin a tiny little curved mirror around at the center. Since the laser will bounce erratically off the surface of the CD, you would read from the disk by placing a thin glass or plastic cover over the CD with a few photosensors sensors around its edge. The returning laser (carrying the data) could strike the cover at any pount, and the internal reflection of the cover would get enough of it to the photosensors to read the data. The laser will zip all over the place, so you'd use timing to ignore the data from non-contiguous parts of the disk. The mirror could be as small as the diameter of the laser, so you could spin it much, much faster than the CD iself could withstand.
The only problem I counld think of for such a device is that I don't think normal optical media will work as expected if you read it at a low angle.
Clearly, since no one seems to have done it, it's not that great of an idea. There's probably something wrong with it that I didn't think about at the time. Oh well - I was 12, and I just wanted to listen to Paul Simon without having to worry about bumping the desk while I was doing my cursed multiplication tables.
In spite of the suggestions and all the tests that I have made, I have not cavato a spider from the hole.
This is a good way to get a fast CDROM drive:
This is based on these rough figures:
Assuming that the scanner is faster than the firewire (400Mbps) and 10% overhead for the data transfer, each cd image will be approx. 7.3 billion bits, taking just over 20 seconds to transfer. This device is a 2,466x speed CDROM "drive". Put that in your Pentium and smoke it! Scanner and algorithm design left as an excercise for the reader.
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.
centripetal force is a force acting toward the centre. in the stone on a string example, it is the force (tension in the string) pulling the stone toward the holder of the string, making it move in a circle. nothing is "travelling about the radius", and nothing is pushing outward from the axis. strings don't push!
centrifugal force is something you get in rotating frames of reference. one doesn't normally use such frames in physics because they are unecessarily complicated. but that is just a matter of calculational convenience; centrifugal forces are real enough in a rotating frame (it is called a fictitious force because it depends on the choice of frame, rather than being intrinsic. see this page). take a fast curve in a car and that fictitious force feels real enough, even if it isn't the simplest way to describe the situation mathematically.
Everything should be made as simple as possible, but not simpler. -- A.E.
Webster's also says that centrifugal (from centr- + Latin fugere to flee) means "proceeding or acting in a direction away from a center or axis"
This is what I remember from Physics 101. However, I may be wrong, seeing as you are the one claiming to be the "physics geek". In any case, however, your definition is contrary to standard, correct English usage.
"Anything is better than IE, and you can quote me on that." -- Wil Wheaton.
There is no "centripetal force." There is, however, a centripetal acceleration, which points *inward*. (Look up the word) You're committing the classic mistake of confusing a force with an acceleration. For example, in your example, the ball's centripetal acceleration is inward. By Newton's 2nd law, a force must be acting on it. The force in this case happens to be the tension of the rope.
There IS centrifugal force. It's a fictional force, which is a sort of misnomer. A fictional force is nothing but a force felt by an object in an accelerating frame of reference, like a ball on a string (since velocity is changing direction), or a car getting on a freeway (since velocity is increasing). The fictional force in your example would be the one felt by the ball, radially outward, with magnitude equal to the tension on the rope.
I think it is you who should have paid attention in physics 101.
There was a noise from the next office like toast popping, and Steve the senior consultant yelled in terror. "Has your toast popped?" I shouted? "Someone just tried to shoot me!" he replied. I walked into his office to see the occupants crowded around an open CD-ROM drive with the shattered remains of about half a CD in it. As we watched, the drive attempted to shut itself, made it about half way, and then opened again. It repeated this process about twice a minute, shutting a little more completely each time. Eventually it fully closed itself, though it is still opening and shutting regularly. We didn't find the other half of the CD (at least some of it is presumably still in the drive and is what was preventing it from closing) but we did find the front flap of the CD-ROM drive under Steve's desk, where it had fallen having been blown clear across the room, past his head, and colliding with his notice-board.
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What cd-roms really need is an eject button which doesnt write home to it's manufacturer (at book rates) for permission to eject a damned disc!
How frustrating it is to push an eject button and watch a device deliberate for several seconds over SOMETHING before ejecting it's cargo!
Basically, that button means "Your work here is done", so give me the disc, OK??