6.3 filename

A filename (also written as two words, file name) is a name used to uniquely identify a computer file stored in a file system. Different file systems impose different restrictions on filename lengths and the allowed characters within filenames.

A filename may include one or more of these components:

The components required to identify a file varies across operating systems, as does the syntax and format for a valid filename.

Discussions of filenames are complicated by a lack of standardisation of the term. Sometimes "filename" is used to mean the entire name, such as the Windows name c:\directory\myfile.txt. Sometimes, it will be used to refer to the components, so the filename in this case would be myfile.txt. Sometimes, it is a reference that excludes an extension, so the filename would be just myfile. Such ambiguity is widespread and this article does not attempt to define any one meaning, and indeed may be using any of these meanings. Some systems will adopt their own standardised nomenclature like "path name", but these too are not standardised across systems.

Around 1962, the Compatible Time-Sharing System introduced the concept of a file (i.e. non-paper file).

Around this same time appeared the dot (period or full-stop) as a filename extension separator, and the limit to three letter extensions might have come from RAD50 16-bit limits.

Traditionally, filenames allowed only alphanumeric characters, but as time progressed, the number of characters allowed increased. This led to compatibility problems when moving files from one file system to another.

Around 1995, VFAT, an extension to the FAT filesystem, was introduced in Windows 95 and Windows NT 3.5. It allowed mixed-case Unicode long filenames (LFNs), in addition to classic "8.3" names.

In 1985, RFC 959 officially defined a pathname to be the character string that must be entered into a file system by a user in order to identify a file.

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