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:( - Lograh — LiveJournal

Tuesday, 16.Jul.2002

17:31 - :(

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drat. I call the photo place and it turns out that their machine can't read CD-RW discs. Just CD-R or Zip discs.

oh well. Time to go pick up the CD-RW I handed them and transferr those files to a CD-R.

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From:lograh
Date:8:30 17.Jul.2002 (UTC)
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There's actually a different material used in the CD-RW discs that allows the reflectivity to be turned on or off by different intensities of light. In the CD-R it is a layer of dye that, once it's reflectivity has been changed it cannot be changed back. In the CD-RW it is a layer of a crystaline substance made from specific various metals. The reason this substance is used is because it has the handy property of, when heated to one temperature and cooled it becomes crystaline, but when heated to a higher temperature and cooled again it reverts to it's basic state. In crystaline form it is reflective, but in the other state it is not.

Now, as for why some older CD drives can't read CD-RW discs we come to the reflectivity of the disc itself. The CD-RW standard only calls for about a third of the reflectivity called for by the CD standard. Thus, in order to read a CD-RW disc properly, the CD drive needs to use extra amplification of the light beam. This was drawn up in the multi-read standard when CD-RW discs were developed, but unfortunately that is not part of the CD standard and all the old drives (as well as some new ones) don't follow it.

Hence the problem taking CD-RW discs to older CD drives.

A more detailed look at CD technology can be found here.
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