The Theory of CD-R and CD-RW

Similar to that used in making photographs, the cyanine and phthalocyanine dyes used in CD-R (CD-Recordable) discs are photosensitive organic compounds. When a CD-R is recorded the dye is heated by the writing laser and becomes opaque (or absorbtive) through a chemical reaction to the heat. Because of this chemical reaction it is not likely that any process will be developed to reverse the process and make previously burned CD-Rs reusable.

CD-RW (CD-Rewritable) uses a different kind of data-bearing layer from that in ordinary CD-R. CD-RW uses a phase change process to alter its state from a reflective state to a light absorbing state. This phase change can be reversed to make the area erasable and reusable. The phase change technology used in CD-RW alters the state of the recording layer from crystaline to non-crystaline and vise versa. The cystaline portion allows the metalized layer to reflect the laser better while the non-crystaline portion absorbs the laser beam making it is not being reflected.

As in pressed CDs and CD-Recordables, these alternating binary states represent the data-bearing signal. In order to achieve these effects in the recording layer, the CD-Rewritable recorder use three different laser powers:

  1. The "Write Power" (the highest laser power) creates a non-crystaline (absorbtive) state on the recording layer.
  2. The "Erase Power" (the middle power) melts the recording layer and converts it to a reflective crystaline state.
  3. The "Read Power" (the lowest power) does not alter the state of the recording layer and it is used for reading the data.

CD-RW discs are not usually readable in most CD-ROM or CD players unless they are "multi-read" compliant. The reason for this is that CD-RW technology emerged a lot later than CD-ROM or CD-R and consequently many older or non-"multi-read" systems do not recognise CD-RW media. CD-R media on the other hand, when finalised, is readable in most recent CD-ROM drives and CD player.


  1. How CD-Recordable and CD-Rewritable Dyes Work, 1996, by Kaz Chigita and Katherine Cochrane, the CD Info Company Inc.
  2. Orange Book part III

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