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Cds and dvds

  1. Nov 16, 2005 #1
    what is the difference between a Cd and a dvd?
    i mean microscopically
    are the holes smaller? different procces altogether?
     
  2. jcsd
  3. Nov 16, 2005 #2

    Danger

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    As far as I know, the only difference is that DVD's use shorter wavelength lasers, and so the spots are closer together and there are more tracks available in the same diameter.
     
  4. Nov 16, 2005 #3

    dduardo

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    The only difference between a pressed CD and DVD is the size of the bumps/pits, depending on which side you look.

    If you are comparing a CDR to a DVDR then the major difference is the photosenstive dye used. When the high power mode laser is writing to the disk the dye reacts and turns dark. When the low power mode laser is reading the light reflects back where it isn't dark and and doesn't reflect back where it is.

    Finally the difference between a CDRW and DVDRW is the active alloy used. In high power mode the laser basically melts the alloy in a specific region and when the cyrstalline stucture cools off it loses its reflectivity. In a lower power mode the crystalline stucture can be reformed to become reflective again.
     
  5. Nov 16, 2005 #4

    Danger

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    I stand corrected. Thanks, ddude. :biggrin:
     
  6. Nov 17, 2005 #5

    DrGreg

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    Are there significant physical differences between DVD+R and DVD-R?

    Or between DVD+RW, DVD-RW and DVD-RAM?
     
  7. Nov 17, 2005 #6

    dduardo

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    DVD+RW and DVD-RAM use a high frequency wobbled grove technique while the DVD-RW uses a lower frequency wobble. In a nutshell the high frequency wobble allows for better data integrity. The +RW and -RAM also have better error correction built in.
     
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