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Establishing the Maximum Speed of a CD-ROM Drive

Posted by michael on from the science-at-its-finest dept.

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)."

15 of 489 comments (clear)

  1. Google cache by awptic · · Score: 5, Informative

    The google cache for this page is here

    1. Re:Google cache by dimator · · Score: 5, Funny

      The karma whore for this story is here

      --
      python -c "x='python -c %sx=%s; print x%%(chr(34),repr(x),chr(34))%s'; print x%(chr(34),repr(x),chr(34))"
  2. If you want to go even faster by Anonymous Coward · · Score: 5, Funny

    you could spin *both* the disc and the reading head (in opposite directions).

  3. What about external support? by jelle · · Score: 5, Insightful

    - 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.
  4. Depends on the age of the CD by Taco+Cowboy · · Score: 5, Interesting



    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 !
  5. Why even spin the disk at all? by gnovos · · Score: 5, Interesting

    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!"
    1. Re:Why even spin the disk at all? by wo1verin3 · · Score: 5, Funny

      something more exact then a laser reading pits and grooves burned into plastic that are invisible to the human eye? Pft...why would CONSUMERS have access to such technology.

    2. Re:Why even spin the disk at all? by anshil · · Score: 5, Insightful

      The beam will bounce off the pit and either scatter or reflect back up into the mirror striking the focal point

      Thats how you learn how CD`s work in school, but it isn't true. In past it was the classical approach of not telling the whole truth to keep others from copying it.

      First the beam is not scattered or reflected, it is _always_ reflected. The CD consits of two layers, the back one is solid and 100% reflective. The distance between the two layers has to be exactly lambda / 4 of the lasers wave length. Now the first layer is semitransparent. Meaning 50% of the light gets through 50% gets reflected. In the first layer you have the pits representing the data. If this layer has a pit 100% of the light gets reflected, but if it hasn't only 50% get through, get reflected at the back layer and then has a destructive interference with the light reflect first. (That's why the distance has to be wavelength/4)

      I fear that the interference will not work if the light is not angeled with 90 degree on the disk.

      How about using 700 Million lasers, not spinning at all? You could read a CD at once :o)

      --

      --
      Karma 50, and all I got was this lousy T-Shirt.
  6. Re:Who would want one? by mgv · · Score: 5, Interesting

    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.
  7. Another Mirror by hendridm · · Score: 5, Informative


    This one has no broken images.

  8. Re:Who would want one? by Waffle+Iron · · Score: 5, Insightful
    The biggest problem with these sort of drives is seek time.

    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.

  9. Bla bla bla by SevenTowers · · Score: 5, Informative

    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
  10. A faster way (2,466x) by labradore · · Score: 5, Interesting

    This is a good way to get a fast CDROM drive:

    1. Buy a 10,000x10,000 dpi scanner with firewire interfeace
    2. Write cdrom image analysis algorithm.
    3. Scan cdrom image into temp hard drive space and analyse, extracting data

    This is based on these rough figures:

    • A cdrom is approximately ( PI*5^2 - PI*0.75^2 )= 76.75 sq. inches of data surface
    • If a cdrom has about 5.6 billion bits on that surface then the density is roughly 76 million bits per square inch.
    • That works out to about 8,800 bits per linear inch. Assume you will need a little better resolution than that because there is some empty space between the dots on a cd surface. 10,000dpi aught to be good enough.

    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.

  11. Re:There's no such thing as centrifugal force. by sweet+reason · · Score: 5, Insightful

    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.
  12. Re:There's no such thing as centrifugal force. by floW+enoL · · Score: 5, Insightful

    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.