Q. Illustrate about Compact Disk Rewritable?

CD-RW optical disk can be repeatedly written and overwritten same as with a magnetic disk. Even though a number of techniques have been tried but only pure optical approach which has proved attractive is known as phase change. Phase change disk uses a material which has two considerably different reflectivities in two different phase states. There is an amorphous state in that molecules display a random orientation and that reflects light poorly and a crystalline state that has a smooth surface which reflects light well. A beam of laser light can alter the material from one phase to other.  Primary shortcoming of phase change optical disks is that material ultimately and permanently loses its desirable properties. Current materials are able to be used for between 500000 and 1000000 erase cycles.

CDRW has obvious benefit over CD-ROM and CD-R that it is able to be rewritten and so used as a true secondary storage.  As it competes with magnetic disk. A key benefit of optical disk is that engineering tolerances for optical disks are much less severe than for high-capacity magnetic disks. So they exhibit higher reliability and longer life.