How does a CD burner rewrite data on a CD-RW disk?

The laser in the CD writer burns "dots" into the inner filling of the disk. This creates binary language that is read by a CD player. Binary is 1s and 0s, which translate into on or off.
The software can translate the binary code into a format recognizable by whatever tool uses the data (music player, MS Word, etc.). A re-writable disk has an inner filling that can be erased (restored to all 0s or 1s) and re-burned into new binary code. These disks can be reused up to 100 times but do cost more. ---------------------- The back side of a single-use CD appears to be a smooth, shiny surface with concentric grooves. But if you observe it under a microscope, you will find that it has a series of pits burned into it, with bumps left between them. The difference in the surface reflectivity is used to represent binary bits (0 or 1). On a rewritable CD, a phase-change alloy is applied to the writing surface. The energy of a laser can "melt" the material into an amorphous state, or re-crystallize it. The difference in reflectivity of the two states creates an analog of the pit-bump of single-use CD's. The reflected patterns are interpreted by the CD reader as binary data. The laser can also restore a location to the opposite state, allowing new data to be encoded.