Welcome to file-extension.com: the free online file extension library. This site includes a detailed database
of file extensions, what they are used for, programs they are associated with, and also provides information
on how to fix file extension related errors.

History of a file extension

A precise outline of the nature and function of file extensions is surprisingly difficult to define, due to over 40 years of developments in computer hardware and software, and the competing influences of Mac, Windows/Dos, and Unix-like operating systems, each with their own file systems and metadata formats.

The earliest implementation of file extensions was by Digital Equipment Corporation, during the early 1960s, which then broke a file name into the base name and the file extension. Eventually this convention was adopted by Microsoft DOS operating systems and then by Windows. As a matter of interest, expressing the base name and file extension as a single name, separated by a full stop, was only a convention for showing both pieces of information together.

More file extension information


In DOS the file extension was stored separately from the base name: a fact that could be seen in the DOS file manager, where the file extension and the name were listed in separate columns. Microsoft originally restricted the base name to eight characters and the file extension to a subsequent three characters: for example BASENAME.FEX. This combination of an 8 letter name with a 3 letter file extension was somewhat restrictive and Windows 95, onwards, allowed longer filenames.

In very simple terms neither UNIX nor Mac operating systems used file extensions. Instead each has had its own file systems, with different conventions for storing metadata, which has changed over time. UNIX systems would store all the information as a single string whilst, up until Mac OS X, Apples would store the data using special code contained within the file.

However, acknowledging that the prevalence of Windows has made the file extension the standard method of expressing a file function (and also reflecting architectural changes to the code made when Mac OS absorbed NeXT Software UNIX based OPENSTEP operating system) Mac OS X now uses file extensions as well.