The name of the write process used by CD-R recorders is "dye sublimation". It works like this: All CD-ROM drives read data based on the differences in reflection of a laser from the surface of the spinning disk. Variations of the reflected light made by small pits in the track are interpreted as data. A special CD-R recordable disk has a layer of polymer dye, over which a reflective coating of gold is then layered. When the CD-R writes data, the laser irradiates a point on the media and the point now has lower reflectivity. To a CD ROM player the response is identical to the pre-made CD. CD-RW disc are similar in construction, differing only in the recording layer-instead of organic dye the recording layer is made up of quarternary phase change alloy consisting of silver, indium, antimony and tellurium (Ag-In-Sb-Te). These
elements make the phase change recording possible.