why need data Compression ?

It is compressed, how the amount of data that is displayed when the data was compressed in a depends on the State. In order to have a huge amount of data, it will be compressed to a larger size. You, a small amount of compressed air, large amounts of compressed data in the form of hold to real space.

Set the amount of data will capture the algorithm used to compress data depends on. If the algorithm is being used properly and in particular data, formatted almost can't take the actual location. Generalized algorithm is used, as if a particular algorithm is data used in a narrow field, may not fit as well. How data will be compressed, the algorithm how much space will it take and how much will be available after data compression is the determining factor.