They store bits as ―pits‖ and ―lands‖ on the surface of the disk that can be detected (read) by a laser beam. They use laser technology to store massive quantity of data in a highly compact form. There are several types:
o CD-ROM (compact disk read only memory)- only read and cannot be erased for re-writing. Has a capacity of 650 MB.
o CD-R (compact disk recordable/WORM (write once read many))- usually blank at first and can be written only once. Has a capacity of 650 MB.
o CD-RW (compact disk rewritable)- can be written and read more than once.
It‘s capacity is 650 MB.
o DVD-ROM (Digital Video Disk)- they are similar to CDs except that it has high quality sound and high-resolution video. It has a capacity of between 4.7 GB and up to 17 GB.