Data Compression

 A modern computer system has lakhs of files on them.n one needs to transfer a large number of these files or an entire directory structure to another computer or storage device.
When one wants to transfer files (containing data or programs or both) to another computer or storage device, the amount of data to be transferred or stored becomes a concern.
 Both computer networks and external storage devices are usually not as fast as internal components of a computer.
Thus, transferring larger amount of data can take more time.
 If the Internet is used for such transfers, more time may be taken in the transfer due to slow Internet speed.
 Also, such transfers put load on the usually clogged Internet connection.
 Unless the user or organization has unlimited Internet plan, higher amount of data may result in higher cost as well.
Similarly, if the files and directories are transferred to a storage device, the amount of the data to be transferred again becomes an issue because of the finite capacity of storage devices and the multiple uses that they are put through. 
Considering these issues, there is a need to reduce the amount of storage space occupied by computer files (and entire directory structures), whenever possible.
From a convenience point of view, in many cases it is also desirable to have a single file to handle rather than a large bunch of files or a complex directory structure.
Computer scientists have developed techniques to place a whole directory structure into a single file for convenience. 
Such a file is called an “archive”. 
They have also developed a number of techniques for reducing the storage requirements of computer files and directory structures. 
These techniques are called data compression. 
Data compression generally works by identifying repetition in the data and encoding the data in a way that reduces or eliminates such repetition. 
Such techniques also identify and eliminate less important information to conserve space.

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