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How do reqritable cd's work?

  1. Nov 16, 2004 #1
    how do rewritable cd's work?

    Well, there was a thread on how general cd's work, but then i wondered how would the rewrittable cd's work? Could someone clear it up for me?
     
    Last edited by a moderator: Nov 16, 2004
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  3. Nov 16, 2004 #2

    Cliff_J

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    There is a dye in the plastic of the recordable CD. The dye is normally transparent and the laser can go right through it and reflect. When the disc is 'burned' the dye is heated and becomes opaque so the laser is no longer reflected in those areas. The dye is only changed opaque in those areas to represent the pits needed to represent the data.

    Cliff
     
  4. Nov 16, 2004 #3

    HallsofIvy

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    But the question was about REWRITEABLE CD's.

    Is the dye made transparent again? How?
     
  5. Nov 16, 2004 #4

    Cliff_J

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  6. Nov 21, 2004 #5
    thx.. for the reply
     
  7. Nov 22, 2004 #6

    HallsofIvy

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    I must confess that when I saw "reqritable", my first thought was "regrettable".

    Yes, I have heard a number of regrettable C.D.s!
     
  8. Nov 22, 2004 #7
    The explanation I saw was that a plastic was either heated by the laser and allowed to cool quick, which made shiny crystals, or heated and allowed to cool slowly, which made an amorphous, less shiny area.

    This sounds vaguely believable, till you add in the fact that there are tens of thousands of such write events per second, and the regions are tinier than the point of a needle, and it all happens on a disc spinning at several hundred or thousand of revs per minute.

    So I prefer to believe that it is a form of magic. That seems much more believable.
     
  9. Dec 30, 2004 #8
    I read that the chemicals in a rewritable can only be changed 100 times.
     
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