Optical Disc

An optical disc is a storage medium from which data is read and to which it is written by lasers. Optical discs can store much more data -- up to 6 gigabytes (6 billion bytes) -- than most portable magnetic media, such as floppies. There are three basic types of optical discs:
CD-ROM : Like audio CDs, CD-ROMs come with data already encoded onto them. The data is permanent and can be read any number of times, but CD-ROMs cannot be modified.
WORM : Stands for write-once, read -many. With a WORM disk drive, you can write data onto a WORM disk, but only once. After that, the WORM disk behaves just like a CD-ROM.
erasable: Optical discs that can be erased and loaded with new data, just like magnetic disks. These are often referred to as EO (erasable optical) disks.
These three technologies are not compatible with one another; each requires a different type of disc drive and disc. Even within one category, there are many competing formats, although CD-ROMs and DVDs are relatively standardized.

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