Optical Disks

More advanced technology created a new disk storage forms. Optical disk is a disk written and read by laser beam. This optical disk has a great impact on today's storage technology. Optical disk does not spin, does not need to move access arms and read/write heads, because a laser beam can be moved electronically. The capacity of the storage is considerably greater than their magnetic disk counterparts, and optical disk storage may eventually replace all magnetic tape and disk storage.
Then how do they work? To write data, a laser beam burns tiny cavities into the surface of a disk to mark bits for data. To read the data, a laser beam scans these areas. There are three forms of optical disks available:

• CD-ROM
  
• WORM
  
• Erasable Optical Disks.

• CD-ROM: CD-ROM (compact disk read only memory) is an optical disk storage that contains text, graphics and hi-fi stereo sound. CD-ROM is a 4.75-inch optical disk storage that can store around 650 MB of data. CD-ROM disk is almost the same as the music CD, but uses different forms of track for data. A CD- ROM drive can read music CD, but a CD player cannot read CD-ROM. CD-ROM is a read-only disk that cannot be written on or erased by the user. In CD- ROM standard, data (text or pictures) cannot be viewed with audio play simultaneously. CD-ROM XA standard can do.

• WORM: A WORM (write once, read many) disk is an optical disk that written on just once by the user's environment and then cannot be overwritten. A WORM disk is ideal for use as archive because it can be read many times, but the data cannot be erased. The storage capacity of WORM disk ranges from 400 MB to 6.4 GB.

• Erasable Optical Disks: This is an optical disk that can be erased and written on repeatedly. An erasable optical disk has a great deal of data capacity. It can store up to 4.6 GB. An erasable optical disk functions like a magnetic disk and has huge capacity, so it will replace the magnetic disk in the future.

CD-ROM XA: CD-ROM eXtended Architecture is an extension of the CD-ROM standard that allows for audio to be played concurrently while viewing data. CD-ROM XA uses a standard CD-ROM player, but requires a CD-ROM XA controller card in the computer.