CD stands for “Compact Disk” is a secondary storage device which can store data up to 700mb on a single disk. It has the size is 4.75 in (12 cm) in diameter.

The saved data on cd can be used anytime depending upon the user need.This standard was projected was Sony and Philips companies and it is the most common storage media in computer world.

Initially, CDs were read-only, but newer technology allows users to record as well. CDs will probably continue to be popular for music recording and playback. A newer technology, the digital versatile disc (DVD), stores much more in the same space and is used for playing back movies.

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The hard disk was invented on September 13, 1956 by IBM team led by Rey Johnson (considered as “father” of the disk drive). Earlier hard disk drives were large and cumbersome devices.