Name: File Extension
Description: A file extension is a suffix to the name of a computer file applied to indicate the type of file format. It gives a human readable identifier for the file; such that users can quickly understand the type of file it is without having to open it. The filename extension associates the file with certain software packages, helping an application program recognise whether it is of a type that it can work with. In some operating systems, such as DOS, a file extension is required, but in others, such as Unix, it is optional. Some operating systems limit the length of the extension and some are case sensitive. On Windows computers, extensions consist of a dot '.' at the end of a file name, typically followed by three letters to identify the type of file. On a Unix based system, the file name is a single string, with the '.' being just another character, and with the file name being of variable-length. A file extension is not a reliable identifier of the format of the file. An extension may be linked to more than one program; they are not assigned by a controlling authority, and can be easily changed.