Re: How do rewriteable cds work?

The CD-RW is not quite the CD you might expect, however. Instead of the 
recording beam burning pits into a metallic or glass strata, the CD-R 
media is coated with a dye that has the same reflective properties as an 
ordinary CD. When the recording laser begins to burn data into the CD-RW 
media, it heats the gold layer and the dye layer beneath. The result of 
heating these areas causes the dye and gold areas to diffuse light in 
exactly the same way that a pit would on a glass master disc or a mass-
produced CD. The CD reader is fooled into thinking a pit exists; but there 
is no actual pit, just a spot of less-reflective disc caused by the 
chemical reaction of heating the dye and gold. When rewriting, a similar 
process erases the previously stored data and records new data over it.