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Definition

A circular optical disc made up of thin platted glass and plastic polycarbonate material.

Description

• Standarad size of disc is 12 cm, center hole is of 1.5 cm and 1.2 mm in thickness.
• Storing of data is done on 1 side in a spiral way of valleys (pits) and plains (lands).
• One CD can store upto 600 MB to 700 MB of data, i.e. equivalent to 80 minutes of uncompressed audio files.
• Speed of the disc determines how fast data can be transfered from the CD.
• CD with 24X speed can transfer 3.6 MB/s, 32X speed can transfer 4.8 MB/s and so on.
• Used to store, publish and distribute information.

Types

CD-ROM (CD - Read Only Memory)

• Contents of CD cannot be erased by the user.
• Access only to the data imprinted by the publisher.
• Commercially used in music and software companies to publish large amount of music CD's and application packages.

CD-R (CD - Recordable)

• Contents can be written only once.
• After that they can be read several times, but cannot be written or erased.

CD-RW(CD - Rewritable)

• Contents on the CD can be written on, read and erased several times.
• Made up of alloys of silver, indium, antimony and tellurium.