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Compact disc: –

A compact disc is a non-magnetic storage device the compact discs use optical technology to store the data therefore, are called optical storage device.

A compact disc is a polished metallic disc with a protective plastic coating. A laser beam is used to make holes called pits on the surface of the discs. To read the data, the cd drive projects thin beams of laser on the CD. The difference in light reflected from the pits and the areas having no pits is sensed by a sensor and is interpreted to read the data on the surface of the disc.

The advantage of using optical technology is that large amount of data is store on optical storage devices as compare to magnetic storage devices a CD can store up to 700 MB of data.

CDs are available in three variations: CD-ROM, CD-R and CD-RW.


CD-ROM refers to compact disc- Read Only Memory. Data or information is recorded at the time of manufacture and it can only be read. A CD ROM cannot be used to record fresh data by the computer.

CD-R: –

CD-R is the short form for compact disc-recordable, Data can be written on it once and can be read whenever required. The data written once cannot be erased.

CD-RW: –

stands for compact Disc-Rewriteable .CD-RW is use to write information over and over again.

i.e., old information can be erased and new information can be written using a CD Writer.

CDs are slow in comparison to Hard disc in getting the information store on them, but they are fast as compare to floppies. They are portable storage devices just like floppies. The data is stored on one side only.

DVD: –

stands for digital versatile disc. It is a device that stores data on both side it read data at a faster rate and can store up to about 25 times more information than a CD. The increase capacity allows DVD to store high quality video and audio

Through DVDs look just like CD, they can hold much more data, for example, a full length movie

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