Even with ever-increasing connection speeds and ever-larger hard drives, transmitting and storing large files can still be a problem for many users. In order to make long documents or large programs easy to store and send, users can compress these files, reducing the space they take up. However, compressing files has a number of disadvantages.
Files typically contain large amounts of data which is either blank or redundant. This can be thought of as the difference between the data which makes up the file and the information in the document itself. File compression software identifies these bytes, removes them and marks their location, reducing the file size. When a user decompresses the file, the program looks for the bytes it has removed and recreates them, restoring the file to its original form.
One of the main disadvantages of file compression is that the decompression process can drain memory and processing resources. Compressed files open more slowly than uncompressed files, and other processes may slow down while they are being opened. For older computers, or if many files are being uncompressed simultaneously, this can lead to significant loss of performance. Files that have to be opened quickly or frequently should be stored in an uncompressed format.
Compressing and decompressing files requires compression software. While most types of compression program can deal with multiple file types, there are some file types which can cause problems if a user does not have the correct software. Compressed files make sending data over the internet practical, but this advantage vanishes if the recipient can't open the file. Fortunately, many decompression utilities are free; users sending a compressed file may want to include a link to the appropriate program in case the recipient does not have it.
Not all files can be usefully compressed. This is particularly the case for image, video and audio files. Because the raw data files for video, audio and images take up so much space, common file types like .jpg and .mp3 already include significant compression. This means that there isn't much for a compression utility to do with these files -- indeed, compressing a video file can actually make it bigger, as the compression utility adds a small amount of data but fails to remove any.