Reading from/writing to a compact disk-recordable (CD-R).
CD-R can be written to only once. A CD-R has four layers. A transparent polycarbonate plastic layer covered with a dye layer which in turn is covered with a reflective aluminum layer. Finally, a thin plastic layer is added for protection. The drive’s read/write head writes by projecting a high-intensity laser beam onto the disk so as to burn (darken) spots of the dye layer along the disk track. The drive’s head reads by projecting a low-intensity laser beam. An unburned dye layer spot passes the projected beam to the aluminum layer which in turn reflects it into a sensor and this is interpreted as a 1. On the other hand, a burned spots absorbs the beam and causes no reflection and this is interpreted as a 0.
