A filename extension is a suffix to the name of a computer file applied to indicate the encoding convention (file format) of its contents. A subsequence, substring, prefix or suffix of a string is a subset of the symbols in a string where the order of the elements is preserved A filename is a special kind of string used to uniquely identify a file stored on the File system of a computer A computer file is a block of Arbitrary Information, or resource for storing information which is available to a Computer program and is usually A file format is a particular way to encode information for storage in a Computer file. In some operating systems (for example Unix) it is a convention, while in some others it is a requirement. Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer In Engineering, a requirement is a singular documented need of what a particular product or service should be or do Some operating systems limit the length of the extension (such as DOS and OS/2, to three characters) while others (such as Unix) do not. DOS, short for "Disk Operating System" is a shorthand term for several closely related Operating systems that dominated the IBM PC compatible market OS/2 is a computer Operating system, initially created by Microsoft and IBM, then later developed by IBM exclusively Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer Some operating systems (for example RISC OS) do not use file extensions. RISC OS is an Operating system originally created by British manufacturer Acorn Computers for their ARM based Computers ranging
Filename extensions can be considered a type of metadata. Metadata ( meta data, or sometimes metainformation) is "data about data" of any sort in any media They are commonly used to infer information about the way data might be stored in the file. The description above is meant to mostly explain the intent of filename extensions: an exact definition, giving the criteria for deciding what part of the file name is its extension, belongs to the rules of the specific filesystem used; usually the extension is the substring which follows the last occurrence, if any, of the dot character (e. In Computing, a file system (often also written as filesystem) is a method for storing and organizing Computer files and the data they contain to make A full stop or period (sometimes stop, full point, decimal point, or dot) is the Punctuation mark commonly placed at the g.
txt is the extension of the filename
html the extension of
mysite. index. html).
On filesystems of mainframe systems such as MVS, VMS, and PC systems such as CP/M and derivative systems such as MS-DOS, the extension is a separate namespace from the filename. Multiple Virtual Storage, more commonly called MVS, was the most commonly used Operating system on the System/370 and System/390 IBM CP/M (Control Program for Microcomputers is an Operating system originally created for Intel 8080 / 85 based Microcomputers by Gary Kildall MS-DOS (short for M icro' s' oft D isk O perating S ystem is an Operating system commercialized by Microsoft. In general a namespace is an abstract container providing context for the items ( Names or Technical terms or Words it holds and allowing disambiguation Under Microsoft's DOS and Windows, some extensions, including
CMD, indicate that a file is an executable program. DOS, short for "Disk Operating System" is a shorthand term for several closely related Operating systems that dominated the IBM PC compatible market Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. In Computing, an executable (file causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a file that only contains This is different from Unix-like operating systems, where a suffix is not a separate namespace, and where even having a suffix is voluntary, as file system permissions are used to decide whether a file is executable. A Unix-like (sometimes shortened to *nix) Operating system is one that behaves in a manner similar to a Unix system while not necessarily conforming Most modern File systems have methods of administering permissions or access rights to specific users and groups of users
With the advent of graphical user interfaces, the issue of file management and interface behavior arose. Microsoft Windows allowed multiple applications to be associated with a given extension, and different actions were available for selecting the required application, such as a context menu offering a choice between viewing, editing or printing the file. A context menu (also contextual menu and shortcut menu) is a menu in a Graphical user interface (GUI that appears upon user interaction such
Pre-OS X versions of the Mac OS disposed of filename extensions entirely, instead using a file type code to identify the file format. Mac OS is the trademarked name for a series of Graphical user interface -based Operating systems developed by Apple Inc A type code is the only mechanism used in pre- Mac OS X versions of the Macintosh Operating system to denote a file's format, in a manner similar Additionally, a creator code was specified to determine which application would be launched when the file's icon was double-clicked. A creator code is a mechanism introduced in pre- Mac OS X versions of the Macintosh Operating system to link a data file to the application program On Computer displays, a computer icon is a small Pictogram. Icons have been used to supplement the normal alphanumerics of the computer A double-click is the act of pressing a Computer mouse button twice quickly without moving the mouse Mac OS X, however, uses filename suffixes, as well as type and creator codes, as a consequence of being derived from the Unix-like NEXTSTEP operating system, which did not have type or creator code support in its file system. Mac OS X (mæk oʊ ɛs tɛn is a line of computer Operating systems developed marketed and sold by Apple Inc, the latest of which is pre-loaded on all currently Nextstep was the original object-oriented, multitasking Operating system that NeXT Computer developed to run on its range of proprietary computers
Filename extensions were used in Digital Equipment Corporation (DEC) operating systems (for example, TOPS-10, OS/8 and RT-11). Digital Equipment Corporation was a pioneering American company in the Computer industry The TOPS-10 System was a computer Operating system from Digital Equipment Corporation (DEC for the PDP-10 released in 1964, the resulting systems OS/8 was the primary Operating system used on the PDP-8 Minicomputer developed by Digital Equipment Corporation of Maynard, Massachusetts RT-11 ('RT' for Real Time) was a small single-user Real-time operating system for the Digital Equipment Corporation PDP-11 family of 16-bit CP/M adopted the convention and MS-DOS, as a re-implementation of CP/M, did so as well. CP/M (Control Program for Microcomputers is an Operating system originally created for Intel 8080 / 85 based Microcomputers by Gary Kildall MS-DOS (short for M icro' s' oft D isk O perating S ystem is an Operating system commercialized by Microsoft.
The DEC operating systems internally split the filename into a "base name" and a filename extension, with the "base name" limited to five to eight characters (initially nine in RSX and VMS) and the extension limited to two or three characters; when a filename/filename extension combination was typed in commands, a dot (. A full stop or period (sometimes stop, full point, decimal point, or dot) is the Punctuation mark commonly placed at the ) was placed between the filename and filename extension. CP/M worked the same way; the filename was limited to eight characters and the filename extension was limited to three characters, with a dot between them. Early versions of the FAT filesystem used in MS-DOS and Microsoft Windows imposed the same limitations. Templateinfobox filesystem whilst covering all 3 file systems please make any style changes to both at the same time Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. This is sometimes referred to as the 8.3 filename convention, and since the word filename is eight letters long and ext is a reasonable abbreviation for extension, it can be generalized as:
FILENAME. An 83 filename (also called a short filename or SFN) is a Filename convention used by old versions of DOS and versions of Microsoft Windows EXT
When doing a file listing, the base name and extension would be separated by spaces, much like this:
Volume in drive A: is LINUX BOOT Volume Serial Number is 2410-07EF Directory for A:\ LDLINUX SYS 5480 1999-04-19 23:24 VMLINUZ 530921 1999-04-19 23:24 BOOT MSG 559 1999-04-19 23:24 EXPERT MSG 668 1999-04-19 23:24 GENERAL MSG 986 1999-04-19 23:24 KICKIT MSG 979 1999-04-19 23:24 PARAM MSG 875 1999-04-19 23:24 RESCUE MSG 1020 1999-04-19 23:24 SYSLINUX CFG 420 1999-04-19 23:24 INITRD IMG 878502 1999-04-19 23:24 10 files 1,420,410 bytes 35,840 bytes free
This use of spaces often led to confusion with novice DOS users, who thought of the ". " as part of the file's identifier, rather than merely a convention for separating the two components of that identifier.
The filename extension was originally used to easily determine the file's generic type. The need to condense a file's type into three characters frequently led to inscrutable extensions. Examples include using
. GFX for graphics files,
. Graphics (from Greek grc [[wiktγραφικός γραφικός]] see -graphy) are Visual presentations on some surface such as a wall TXT for plain text, and
. In Computing, plain text is a term used for an ordinary "unformatted" sequential file readable as textual material without much processing MUS for music. Music is an Art form in which the medium is Sound organized in Time. However, because many different software programs have been made that all handle these data types (and others) in a variety of ways, filename extensions started to become closely associated with certain products—even specific product versions. For example, early WordStar files used
. WordStar was a Word processor application published by MicroPro, originally written for the CP/M operating system but later ported to DOS, that WS or
. WSn, where n was the program's version number. Also, filename extensions began to conflict between separate files. One example is
. rpm, used for both RPM Package Manager packages and RealPlayer Media files; others being
. RPM Package Manager ( Red Hat Package Manager, abbreviated RPM) is a Package management system. RealPlayer (briefly known also as RealOne Player) is a proprietary Cross-platform media player by RealNetworks that plays a number qif, shared by DESQview fonts, Quicken financial ledgers, and QuickTime pictures,, and
. DESQview was a Text mode multitasking program developed by Quarterdeck Office Systems which enjoyed modest popularity in the late 1980s and early 1990s Intuit Inc ( is an American Software company that develops financial and Tax preparation software and related services for Small A ledger or lieger (from the English dialect forms liggen or leggen, to lie or lay in sense adapted from the Dutch substantive QuickTime is a Multimedia framework developed by Apple Inc, capable of handling various formats of Digital video, Media clips sound text gba, shared between GrabIt scripts and Game Boy Advance emulators. GrabIt is a Windows -based Freeware newsreader programmed and developed by Ilan Shemes The Game Boy Advance (often shortened to GBA) is a 32-bit handheld video game console developed manufactured and marketed by Nintendo. 
Some other operating systems such as Multics that used filename extensions generally had much more liberal sizes for filenames. Multics ( Mult iplexed I nformation and C omputing S ervice was an extremely influential early Time-sharing Operating system Many allowed full filename lengths of 14 or more characters, and maximum name lengths up to 255 were not uncommon. The file systems in operating systems such as Unix stored the file name as a single string, not split into base name and extension components, with the '. Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer ' being just another character allowed in file names. Such systems generally allow for variable-length filenames, permitting more than one dot, and hence multiple suffixes. Some components of Multics and Unix, and applications running on them, used suffixes, in some cases, to indicate file types, but they did not use them as much — for example, executables and ordinary text files had no suffixes in their names.
The High Performance File System (HPFS), used in Microsoft and IBM's OS/2 also supported long file names, and didn't divide the file name into a name and an extension. HPFS or High Performance File System is a File system created specifically for the OS/2 Operating system to improve upon the limitations International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology OS/2 is a computer Operating system, initially created by Microsoft and IBM, then later developed by IBM exclusively However, the convention of using suffixes continued, even though HPFS supported extended attributes for files, allowing a file's type to be stored with the file as an extended attribute.
In addition, Microsoft's Windows NT's native file system, NTFS, supported long file names and didn't divide the file name into a name and an extension, but again, the convention of using suffixes to simulate extensions continued, for compatibility with existing versions of Windows. Windows NT is a family of Operating systems produced by Microsoft, the first version of which was released in July 1993 NTFS (New Technology File System Is the standard File system of Windows NT, including its later versions Windows 2000, Windows XP, Windows
As the Internet age arrived, it was possible to discern who was using Windows systems to edit their web pages versus who used Macintosh or Unix computers, since the Windows users were generally restricted to ending their web page filenames in
. The Internet is a global system of interconnected Computer networks Macintosh, commonly nicknamed Mac is a Brand name which covers several lines of Personal computers designed developed and marketed by Apple Inc HTM (instead of
. html). This also became a problem with programmers experimenting with the Java programming language, since it required source code files to have the four-letter suffix
. In Computer science, source code (commonly just source or code) is any sequence of statements or declarations written in some Human-readable java and compiled object code output files to have the five-letter
. A compiler is a Computer program (or set of programs that translates text written in a computer language (the source language) into another In Computer science, object code, or an object file, is the representation of code that a Compiler or Assembler generates by processing class suffix.
Eventually, Windows introduced support for long file names, and removed the 8. Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. 3 name/extension split in file names, in an extended version of the commonly used FAT file system called VFAT. Templateinfobox filesystem whilst covering all 3 file systems please make any style changes to both at the same time In Computing, a file system (often also written as filesystem) is a method for storing and organizing Computer files and the data they contain to make VFAT first appeared in Windows NT 3.5 and Windows 95. Windows NT 35 is the second release of the Microsoft Windows NT Operating system. Windows 95 is a consumer-oriented Graphical user interface -based Operating system. The internal implementation of long file names in VFAT is largely considered to be a kludge, but it removed the important length restriction, and allowed files to have a mix of upper case and lower case letters, on machines that would not run Windows NT well. A kludge (alternately kluge) is a clumsy or inelegant solution to a problem or difficulty Capital letters or majuscules pronunciation /məˈdʒʌskyuls ˈmædʒəˌskyuls/ in the Roman alphabet A, B, C, D, Lower case (also lower-case or lowercase) minuscule, or small letters are the smaller form of letters as opposed to upper Windows NT is a family of Operating systems produced by Microsoft, the first version of which was released in July 1993 However, the use of three-character extensions under Microsoft Windows has continued, originally for backward compatibility with older versions of Windows and now by habit, along with the problems it creates.
The default behavior of Windows Explorer, the file browser provided with Windows, is for file extensions not to be shown. Malicious users have tried to spread computer viruses and computer worms by using file names formed like
LOVE-LETTER-FOR-YOU.TXT.vbs. A computer virus is a Computer program that can copy itself and infect a computer without permission or knowledge of the user A computer worm is a self-replicating Computer program. It uses a network to send copies of itself to other nodes (computer terminals on the network and it may do so without The ILOVEYOU virus also known as VBS/Loveletter and Love Bug virus is a Computer virus written in VBScript. The hope is that this will appear as
LOVE-LETTER-FOR-YOU. TXT, a harmless text file, without alerting the user to the fact that it is a harmful computer program, in this case written in VBScript. VBScript (short for Visual Basic Scripting Edition) is an Active Scripting language developed by Microsoft.
Some similar historical Microsoft Windows security issues are discussed under COM file.
Later Windows versions (starting with Windows XP Service Pack 2 and Windows Server 2003) included customizable lists of file extensions that should be considered 'dangerous' in certain 'zones' of operation, such as when downloaded from the web or received as an e-mail attachment. Windows XP is a family of 32-bit and 64-bit Operating systems produced by Microsoft for use on Personal computers including home and Windows Server 2003 (also referred to as Win2K3 is a server Operating system produced by Microsoft. To download is to receive data from a remote or central system such as a Webserver, FTP server, mail server or other similar systems The World Wide Web (commonly shortened to the Web) is a system of interlinked Hypertext documents accessed via the Internet. Modern antivirus software systems also help to defend users against such attempted attacks where possible.
There have been instances of malware crafted to exploit vulnerabilities in some Windows applications which could cause a stack-based buffer overflow when opening a file with an overly long, unhandled file extension. Malware, a Portmanteau word from the words '''mal'''icious and soft'''ware''', is software designed to infiltrate or damage a computer system without In Computer security and programming, a buffer overflow, or buffer overrun, is an anomalous condition where a process attempts to
In network contexts, files are regarded as streams of bits and do not have filenames or extensions. A bitstream or bit stream is a Time series of Bits A Bytestream is a series of Bytes typically of 8 bits each and can be
In the internet protocol suite the information about a certain type relating to a certain bitstream is encoded in the MIME Content-type of the stream, represented by a row of text in a block of text preceding the stream, such as:
BeOS, whose BFS file system supports extended attributes, would tag a file with its MIME Content-type as an extended attribute. The Internet Protocol Suite (commonly TCP/IP) is the set of Communications protocols used for the Internet and other similar networks Multipurpose Internet Mail Extensions ( MIME) is an Internet standard that extends the format of e-mail to support text in Character BeOS is an Operating system for Personal computers which began development by Be Inc The KDE and GNOME desktop environments associate a MIME Content-type with a file by examining both the filename suffix and the contents of the file, in the fashion of the file command, as a heuristic. KDE ( K Desktop Environment) (ˌkeɪdiːˈiː is a Free software project which aims to be a powerful system for an easy-to-use Desktop environment. A gnome is a Mythical creature characterized by its extremely small size and subterranean lifestyle In graphical computing a desktop environment ( DE) commonly refers to a style of Graphical user interface (GUI that is based on the Desktop metaphor which file is a standard Unix program for determining the type of data contained in a Computer file. heuristic (hyu̇-ˈris-tik is a method to help solve a problem commonly an informal method They choose the application to launch when a file is opened based on the MIME Content-type, reducing the dependency on filename extensions. Mac OS X uses both filename extensions and mime types, as well as file type codes, to select a Uniform Type Identifier by which to identify the file type internally. Mac OS X (mæk oʊ ɛs tɛn is a line of computer Operating systems developed marketed and sold by Apple Inc, the latest of which is pre-loaded on all currently OSType (also known as FourCC or ResType) is the name of a four-byte sequence commonly used as an identifier in Mac OS. A Uniform Type Identifier ( UTI) is a string defined by Apple Inc