OPTICAL Discs use tiny etched on the surface of a circular disc to store information. This information is read by illuminating the surface with laser light and observing reflections. Optical storage is non volatile and access to the information is sequential. The following forms are currently common in use:

• CD, CD-ROM, DVD, and BLU-ray discs, HD DVD: These are read only optical storage used for mass distribution of digital information such as computer programs, music, video and pictures.
• CD-RW, DVD-RW, DVD+RW, DVD-RAM: These are re-writeable slow-write, fast read storage used for tertiary and off-line storage.
• CD-R, DVD-R, DVD+R, WORM: These write once storage devices are used for tertiary and off-line storage.