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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).
...with more lasers.
~shiny
WILL HACK FOR $$$
- 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.
Muchas Gracias, Señor Edward Snowden !
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!
"Your superior intellect is no match for our puny weapons!"
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.
I realize there are technical hurdles with this idea, but I think they are possible to overcome: use varying luminosity bits.
Right now what they use is On-Reflective Off-Non Reflective. If the laser was able to detect that some of the bits were at 50% reflectivity, then you'd have 2 bits of data for every bit of reflectivity on the surface.
If one were to get fancier, they could use multi-colored bits. Using 2 lasers instead of one, then one laser would read a different value than the other depending on how the surface reacted to the light. They may already be doing that today with DVD's, I'm not really sure. It's been a while since I read up on it.
I guess the real point to what I'm saying is that increasing the density of the data and the spin of the disk aren't the only two options.
"Derp de derp."
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.
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"
I don't know ... you don't happen to teach shop class and have only 7 fingers do you?
Karma? Karma? I don't need no stinkin' karma.
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.
You said:
"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."
My experience with my CDROM and CDRW drive (Samsung 52X CDROM drive and Sony 16X/10X/40X CDRW drive) is that whenever I put a disk into it, during the SEARCH, the drives will SPIN VERY FAST - I can even hear the whrrrrrlllll sound ! - then it'll slow down, if the drive finds out that the disk is an Audio CD.
What matters is that my OLD audio CDs may NOT even survive the FAST spin during the SEARCH routine.
Muchas Gracias, Señor Edward Snowden !
What they need to do is put miniature black holes in the center of the spindle to cancel out some of the centrifugal force. Also, you could let the black hole out of the CD-ROM drive when you weren't using it and it would clean your room for you!
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.
In fact it's basically possible to get instant loads - it only depends on how creative you get.
Just like the bandwidth vs latency issue in network connections, all we need to do is add more data paths.
Can't spin the disc at 100x? Well, spin it at 50X and use 2 lasers (I know the first 50x drives did something like this, they were just REALLY buggy at the time). Can't spin at 200X? Use 4 lasers. Can't fit any more lasers in? Take a picture!
I'm really amazed that we don't have these already actually - we'll need em sooner or later, unless we change to all solid state electronics...
without having to alter existing cd fabrication technologies you could reach much higher speeds if you rotate the cd near its maximum and then rotate the laser in an opposing direction at or near its maximum. Now you can add the two maximums together and you have a MUCH faster cdrom drive.
Much louder too, of course. But getting cdreaders quiet is easy... its just that manufacturers prefer to make cheap drives instead of quiet ones.
Ever need an online dictionary?
I bet you're the guy with a queue forming behind him at the computer store, arguing the fact that your 17" monitor is only 16" when measured diagonally, too :)
"If you create user accounts, by default, they will have an account type of Administrator with no password." KB Q293834
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.
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."
A use for all those AOL CD's that I have.
Cause after a while you have enough coasters.
-THIS SPACE FOR RENT!
The Kenwood 72x drive is quite fast.
What it does is to spin the drive slower, but read 7 tracks in parallel. Now if they could get two read heads like this, it would be a 142x drive without having to spin the cd any faster.
Here's the info.
This is actually what happens with Linux; it's called the buffer cache and page cache. One's (disk-)block oriented and the other's (memory-)page oriented. They work (well) with other media, too. I'll stay scarce on the details since a) I don't know them and b) it's probably changing in 2.5
Lots of SCSI disks, controllers, and (yes) cdroms have their own ram cache. Just not 640MB worth.
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.
Some points:-Yarn - Rio Karma: Excellent
Seems to me that this would be an excellent way to ensure that your data is permenantly deleted...
*Condense fact from the vapor of nuance*
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??
Broadband is nice.
Broadband is nice but expensive. What would you rather pay, $60 for a CD-ROM drive plus an install set, or $200,000 for a house in an area served by broadband?
I rarely use my CD-ROM to install software, since 'apt-get' directly off HTTP is almost as fast
"Rarely" meaning "only for games," right? Most PC games are non-free because artists, musicians, and level designers have a tougher time accepting the free software or open source philosophy than coders do. Because they sell their product at retail, they have 700 MB (capacity of a CD) to work in rather than 20 MB (the maximum attention span of a user behind 56K). (The fact that PC games are available primarily for Windows is beside my point, partly because Wine can run the vast majority of 2D Windows games.)
Will I retire or break 10K?
...although there is fragmentation of CD-ROMs as they are spun faster and faster...
A friend of mine worked at CompUSA for a couple of months. He said that people would frequently return certain brands of CDRWs because the discs would shatter in their drives. I forgot which brand exactly, but I think it was some of those cool looking black CDs.
-- dan.sherman