Reading from/writing to a compact disk-rewritable (CD-RW).
CD-RW can be written to as wished. A CD-RW has four layers. A transparent polycarbonate plastic layer covered with a chemical 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 melt spots of the chemical layer along the disk track. The drive’s head reads by projecting a low-intensity laser beam. A solid spot of the chemical layer 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 liquid spot of the chemical layer absorbs the beam and causes no reflection and this is interpreted as a 0. Before rewriting on a CD-RW, first it has to be erased. The drive’s head erases by projecting a medium-intensity laser beam onto the disk so as to solidify the melted spots of the chemical layer.
