Compression is a process of transforming more files in only one file, smaller than in their original form by using a compression algorithm. The compressed files help us to download copy or share faster and easier the specific files on a computer. Also, once the files are compressed, you can store more data on a removable media.

Extensions:

The most used are: .ZIP, .RAR, .ARJ, .TAR, .GZ and .TGZ. Besides these you can also find:

.ace      .c01      .gz      .sit          .uu

.ain       .c02      .hqx     .sitx        .uue

.alz       .car       .iso      .tar.gz     .z    

.ar        .cbz       .lha     .tbz         .zip    

.arc       .cpt      .lzh      .tbz2       .zoo 

.ari        .dar      .mim     .tgz        .000

.arj        .dd       .mme                 .7z 

.as        .deb      .pak 

.bh        .dgc      .pf 

.bhx       .dist      .rar 

.b64       .ecs      .sea 

.btoa      .efv  

.bz 

To view the compressed files, you need a compatible decompression program that can read these codes and convert the data back to its original form.

For Windows XP, or any other later operating systems, users can compress files simply selecting the file, Right click on it then Send to / Compressed folder, as these operating systems include the compression option. File will be saved with a .zip extension. For the other windows versions, users must download and install this utility.Concerning the Linux or Unix operating systems, these have both a command that can compress and uncompress the files.

We can distinguish two types of compression methods: 

Lossy compression
Loosy compression method is when after a compression and a decompression, the files resulted loses from its quality, but it is still useful. The multimedia data like audio and video are the most exposed to the lossy compression. If the same file is compressed and decompressed repeatedly, the file will progressively loose quality and after a time might be useless.

Lossless data compression
Lossless data compression is the opposite of lossy compression. This method is based on algorithms that reconstruct the original data after compression. Some image file formats like .png and .gif use only lossless data compression.