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A filename, or file name, is the name of a file stored within the parameters of a file system.


In many operating systems, including Unix, OpenVMS, Microsoft Windows, and Linux, the filename may be followed by a period and a filename extension of one or more characters to indicate the kind of data stored in the file. Older operating systems, such as MS-DOS, did not support extensions longer than three characters. Examples include "c" for C source code, "ps" for PostScript, and "txt" for plain text.[1]

Mac filenames[]

Classic Mac OS avoided relying on filename extensions, and identified file types and their associated applications through type and creator codes, respectively. The codes each consisted of 4 alphanumeric characters that were normally hidden from end users, and required a utility, such as ResEdit, to modify them.[2]

The first Macintosh File System (MFS), released in 1984, internally supported filenames up to 255 characters, but the Finder only supported 63 characters. On September 17, 1985, it was superseded by the Hierarchical File System (HFS) in System 2.1, which reduced the filename limit to 31 characters. Support for 255 character file names returned in HFS Plus, which was introduced with Mac OS 8.1 on January 19, 1998. However, the Finder's 31-character limit was not revised until Mac OS X, which was commercially released on March 24, 2001.[3]


  1. Filename extension at the Free On-Line Dictionary Of Computing. 2002-04-19.
  2. Type/Creator Database by Ilan Szekely, 2003-10-23.
  3. On the Macintosh File System by Stephen Hackett, 512 Pixels. 2012-02-25.

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