Compression is a technique for replacing redundant patterns with a single instance of the pattern. The resulting file or data is lesser in terms of its size when compared with the original one. The ratio between the original and compressed size is known as its compression ratio. Compressing file sizes is very important for transfer of data over a low bandwidth medium. Compressed files take lesser time than those of the original files. Email service providers normally maintain a hard upper limit for attachment limit size. Therefore it is very important to compress file sizes for these attachments to fit the upload limit constraint.
To compress file sizes the user must use special file compression or archiving software. These soft wares implement sophisticated compression algorithms and other optimizations to reduce file sizes. Some of the Lossy Algorithms (Loss of data during compression) are JPEG, JBIG2 etc. Popular Lossless algorithms (No Loss of data during compression) are LZW, ZIP, RLE etc. Lossless algorithms are used to compress textual information in files. Most of them maintain a dictionary of carefully picked patterns and replace them in the main text. JPEG2000 is a type of lossless compression used for compressing images. Reductions in image size, color depth can reduce the size of the image till some extent.
After prolonged usage of a single operating system, the files begin to stack up and keep increasing in numbers. Documents and other files keep stacking up as well. The need to compress file sizes in this case is of utmost importance. Windows provides a built in backup tool, to backup files and folders. This tool also compresses the backed up data. Otherwise, right clicking a partition in the hard drive will give an option to compress files. NTFS (New Technology File System) also provides an option to compress the file system itself and hence compress file sizes. Different operating systems like Windows and Linux use different programs for compression of files. There are different programs in Linux to compress file sizes. As a rule of thumb, the complexity of the document is the deciding factor for the final compression ratio.