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Encyclopedia > Filename extension

A filename extension is a suffix to the name of a computer file applied to indicate its type. It is commonly used to infer information about what sort of data might be stored in the file. The description above is meant to mostly explain the intent of filename extensions: a true definition, giving the criterion for deciding what part of the file name is its extension, belongs to the rules of the specific filesystem used; most times the extension is the substring which follows the last occurrence, if any, of the dot character (e.g. "txt" is the extension of the filename "readme.txt", "html" the extension of "mysite.index.html"). On filesystems on mainframe systems such as MVS, VMS, and PC systems such as CP/M and derivative systems such as Microsoft DOS, the extension is actually a separate namespace from the filename. This is different from Unix-like operating systems, where filesystems do not actually support the notion of an extension, where a suffix is not a separate namespace, and where even having a suffix is voluntary for executables, as permissions are used to decide whether a file is executable. A substring of a string is a string such that . ... A filename is a special kind of string used to uniquely identify a file stored on the file system of a computer. ... This article is about computer files and file systems in general terms. ... A file format is a particular way to encode information for storage in a computer file. ... See Filing system for this term as it is used in libraries and offices In computing, a file system is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. ... A full stop or period (sometimes stop, full point or dot), is the punctuation mark commonly placed at the end of several different types of sentences in English and many other languages. ... MVS (Multiple Virtual Storage) was the most commonly used operating system on the System/370 and System/390 IBM mainframe computers. ... VMS is a three-letter abbreviation with multiple meanings, as described below: Virtual Memory System (another name for OpenVMS), an operating system Variable message sign, an electronic traffic sign often used on highways Visual Memory System (better known as Visual Memory Unit), a storage device for the Sega Dreamcast console... CP/M is an operating system originally created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc. ... Disk Operating System (specifically) and disk operating system (generically), most often abbreviated as DOS (not to be confused with the DOS family of disk operating systems for the IBM PC compatible platform), refer to operating system software used in most computers that provides the abstraction and management of secondary storage... Diagram of the relationships between several Unix-like systems A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. ... Most modern file systems have methods of administering permissions or access rights to specific users and groups of users. ...


With the advent of the GUI, the issue of file management and interface behavior arose. The Windows platform allowed multiple applications to be associated with a given filename extension, and different "actions," using those applications, defined for opening, editing, viewing, and so-forth by means of a context menu. File managers such as Windows Explorer can have applications assigned for any extension. For example, a text editor for .txt, a word processor for .doc or .odt, a web browser for .htm or .html, PDF viewer or editor for .pdf, a graphics program for .png, .gif or .jpg, a spreadsheet program for .xls or .ods, etc. GUI redirects here. ... An example of a context menu taken from the word processor Microsoft Word. ... For the Windows 3. ... Windows Explorer running on Windows Vista Windows Explorer running on Windows XP Windows Explorer is an application that is part of modern versions of the Microsoft Windows operating system that provides a graphical user interface for accessing the file systems. ... Notepad is the standard text editor for Microsoft Windows A text editor is a piece of computer software for editing plain text. ... A word processor (also more formally known as a document preparation system) is a computer application used for the production (including composition, editing, formatting, and possibly printing) of any sort of viewable or printed material. ... An example of a Web browser (Mozilla Firefox) A web browser is a software application that enables a user to display and interact with text, images, videos, music and other information typically located on a Web page at a website on the World Wide Web or a local area network. ... “PDF” redirects here. ... A graphics program is a piece of computer software that enables a user to modify or view graphics files. ... Screenshot of a spreadsheet under OpenOffice A spreadsheet is a rectangular table (or grid) of information, often financial information. ...


Under Microsoft's operating systems DOS and Windows, some extensions, including .exe, .com, .bat, and .cmd, indicate that a file is an executable program. Disk Operating System (specifically) and disk operating system (generically), most often abbreviated as DOS (not to be confused with the DOS family of disk operating systems for the IBM PC compatible platform), refer to operating system software used in most computers that provides the abstraction and management of secondary storage... Windows redirects here. ...


Filename extensions have been in use for decades, but they have gained common usage because the file systems included with DOS and Windows had severe limitations on filename lengths for many years, which strongly encouraged the use of filename extensions. Filename extensions can be considered as a type of metadata. For library and office filing systems, see Library classification. ... Metadata is data about data. ...


Pre-OS X versions of the Mac OS disposed of filename extensions entirely, instead using a file type code to identify the file format. Additionally, a creator code was specified to determine which application would be launched when the file's icon was double-clicked. Mac OS X, however, uses filename suffixes as a consequence of being derived from the Unix-like NEXTSTEP operating system, which didn't have type or creator code support in its file system. This article relates to both the original Classic Mac OS as well as Mac OS X, Apples more recent operating system. ... A type code is a mechanism used in pre-Mac OS X versions of the Macintosh operating system to denote a files format, in a manner similar to file extensions in other operating systems. ... A creator code is a mechanism used in pre-Mac OS X versions of the Macintosh operating system to link a data file to the application program which created it, in a manner similar to file extensions in other operating systems. ... Nuvola icons for KDE are available as PNG images, which come in six sizes, and SVG images, which are scalable On computer displays, a computer icon is a small pictogram. ... Mouse properties in GNOME, with a setting for double-click speed A double-click is the act of pressing a computer mouse button twice quickly without moving the mouse. ... Mac OS X (pronounced ) is a line of graphical operating systems developed, marketed, and sold by Apple Inc. ... NEXTSTEP is the original object-oriented, multitasking operating system that NeXT Computer, Inc. ...

Contents

Historical limitations

Filename extensions were used in Digital Equipment Corporation (DEC) operating systems (for example, TOPS-10, OS/8 and RT-11). CP/M adopted the convention and MS-DOS, as a re-implementation of CP/M, did so as well. The DEC logo 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 and later on for the DEC-System10. ... OS/8 was the primary operating system used on the Digital PDP-8 minicomputer. ... RT-11 (for Run Time or Real Time) was a real-time operating system for the DEC PDP-11. ... CP/M is an operating system originally created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc. ... Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ...


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 (actually nine in RSX and VMS, initially) and the extension limited to two or three characters; when a filename/filename extension combination was typed in commands, a period (.) 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 period between them. Early versions of the FAT filesystem used in MS-DOS and Microsoft Windows imposed the same limitations. 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: A full stop or period (sometimes stop, full point or dot), is the punctuation mark commonly placed at the end of several different types of sentences in English and many other languages. ... File Allocation Table (FAT) is a partially patented file system developed by Microsoft for MS-DOS and was the primary file system for consumer versions of Microsoft Windows up to and including Windows Me. ... Windows redirects here. ... A 8. ...

FILENAME.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 need for more

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, .TXT for plain text, and .MUS for music. 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 .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; another being .qif shared by both Quicken Information Files (financial ledgers) and QuickTime Image Format (pictures). Graphic redirects here. ... Computer files can be divided into two broad categories: binary and text. ... For other uses, see Music (disambiguation). ... WordStar was a word processor application, published by MicroPro, originally written for the CP/M operating system but later ported to DOS, that enjoyed a dominant market share during the early to mid-1980s. ... RPM Package Manager (originally Red Hat Package Manager, abbreviated RPM) is a package management system. ... RealPlayer, briefly known also as RealOne Player, is a cross-platform media player by RealNetworks that plays a number of multimedia formats including MP3, MPEG-4, QuickTime, Windows Media and multiple versions of proprietary RealAudio and RealVideo formats. ... Intuit Logo Intuit, Inc. ... A ledger (from the English dialect forms liggen or leggen, to lie or lay; in sense adapted from the Dutch substantive logger), is the principal book for recording transactions. ... QuickTime is a multimedia framework developed by Apple Inc. ...


As time went on, hundreds of different extensions came into use as software developers invented more and more file formats. This led to reference manuals being published, devoted entirely to listing the extensions and the type (or types) of data that might be found in files so named. These issues led to the need for alternative systems with significantly lower chances of conflicts.


Some other operating systems, such as Multics that used filename extensions generally had much more liberal sizes for filenames. 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 '.' 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 didn't use them as much - for example, programs and ordinary text files had no suffixes in their names. Multics (Multiplexed Information and Computing Service) was an extraordinarily influential early time-sharing operating system. ... Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®, sometimes also written as or ® with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ...


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. 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. HPFS or High Performance File System is a file system created specifically for the OS/2 operating system to improve upon the limitations of the FAT file system. ... For other uses, see IBM (disambiguation) and Big Blue. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...


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 (New Technology) is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. ... NTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, and Windows Vista. ...


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 .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 .java and compiled object code output files to have the five-letter .class suffix. The first Macintosh computer, introduced in 1984, upgraded to a 512K Fat Mac. The Macintosh or Mac, is a line of personal computers designed, developed, manufactured, and marketed by Apple Computer. ... Java language redirects here. ... Source code (commonly just source or code) is any series of statements written in some human-readable computer programming language. ... A diagram of the operation of a typical multi-language, multi-target compiler. ... In computer science, object file or object code is an intermediate representation of code generated by a compiler after it processes a source code file. ...


Eventually, Microsoft introduced support for long file names, and removed the 8.3 name/extension split in file names, in an extended version of the commonly used FAT file system called VFAT. VFAT first appeared in Windows NT 3.5 and Windows 95. The internal implementation of long file names in VFAT is largely considered to be an ugly 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. However, the use of three character extensions under Windows has continued, originally for backward compatibility with older versions of Windows and now by habit, along with the problems it creates. Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... File Allocation Table (FAT) is a partially patented file system developed by Microsoft for MS-DOS and was the primary file system for consumer versions of Microsoft Windows up to and including Windows Me. ... For library and office filing systems, see Library classification. ... Windows NT 3. ... Windows 95 is a consumer-oriented graphical user interface-based operating system. ... This article does not cite any references or sources. ... Majuscules or capital letters (in the Roman alphabet: A, B, C, ...) are one type of case in a writing system. ... Minuscule, or lower case, is the smaller form (case) of letters (in the Roman alphabet: a, b, c, ...). Originally alphabets were written entirely in majuscule (capital) letters which were spaced between well-defined upper and lower bounds. ... Windows NT (New Technology) is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. ...


Security issues

The default behavior of Windows Explorer, the Microsoft file browser, 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. 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. 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. ... 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. In MS-DOS and compatible DOSes, and in 8-bit CP/M, a COM file is a simple type of executable 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, received as an e-mail attachment etc. Modern antivirus software systems also help to defend users against such attempted attacks where possible. Windows XP is a line of operating systems developed by Microsoft for use on general-purpose computer systems, including home and business desktops, notebook computers, and media centers. ... Windows Server 2003 is a server operating system produced by Microsoft. ... This article is about the computer terms. ... WWWs historical logo designed by Robert Cailliau The World Wide Web (commonly shortened to the Web) is a system of interlinked, hypertext documents accessed via the Internet. ... Antivirus redirects here. ...


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 is software designed to infiltrate or damage a computer system without the owners informed consent. ... In computer security and programming, a buffer overflow, or buffer overrun, is a programming error which may result in a memory access exception and program termination, or in the event of the user being malicious, a possible breach of system security. ...


Relation to Internet content types

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. ...


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: The Internet protocol suite is the set of communications protocols that implement the protocol stack on which the Internet and most commercial networks run. ... For mime as an art form, see mime artist. ...

 Content-type: text/plain 

BeOS, whose BFS file system supports extended attributes, would tag a file with its MIME Content-type as an extended attribute. The KDE and GNOME desktop environments associate a MIME Content-type with a file by examining the filename suffix and examining the contents of the file, in the fashion of the file command, as a heuristic. 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. BeOS is an operating system for personal computers which began development by Be Inc. ... The Be File System (BFS, occasionally misnamed as BeFS) is the native file system for the BeOS operating system. ... For the NYSE stock ticker symbol KDE, see 4Kids Entertainment. ... This article is about the mythical creature. ... Information in this article or section has not been verified against sources and may not be reliable. ... file is a program originated in Unix that runs under the shell (command-line) to determine the file type heuristically instead of other simpler ways to classify it, like with file extensions, MIMEs, etc. ... For other uses, see Heuristic (disambiguation). ... Mac OS X (pronounced ) is a line of graphical operating systems developed, marketed, and sold by Apple Inc. ... OSType (also known as FourCC or ResType) is the name of a four-byte type commonly used as an identifier in Mac OS. The four bytes could in principle have any binary value, though they are usually ASCII or characters from the Mac Roman character set. ... A Uniform Type Identifier (UTI) is a string that uniquely identifies the type of a class of items. ...


See also

This is a list of file formats organized by type, as can be found on computers. ... Internet media (MIME) type Categories: | | | ... A file format is a particular way to encode information for storage in a computer file. ... file is a program originated in Unix that runs under the shell (command-line) to determine the file type heuristically instead of other simpler ways to classify it, like with file extensions, MIMEs, etc. ... Metadata is data about data. ... There are very few or no other articles that link to this one. ... A type code is a mechanism used in pre-Mac OS X versions of the Macintosh operating system to denote a files format, in a manner similar to file extensions in other operating systems. ... A creator code is a mechanism used in pre-Mac OS X versions of the Macintosh operating system to link a data file to the application program which created it, in a manner similar to file extensions in other operating systems. ...

External links


  Results from FactBites:
 
Saugus.net: Glossary of Computer File Extensions (9997 words)
This is a generic sort of extension indicating some sort of hexadecimal (or even binary) data; of particular note though is that interactive fiction data files for use with the Hugo program typically use this extension.
This is a generic sort of extension indicating "library" data; of particular note though is that native Amiga font files often use this extension.
This is a generic sort of extension indicating some sort of "type" data; of particular note though is that native Amiga font files often use this extension.
Filename extension - Wikipedia, the free encyclopedia (1563 words)
Filename extensions have been in use for decades, but they have gained common usage because the file systems included with DOS and Windows had severe limitations on filenames for many years, which strongly encouraged the use of filename extensions.
Filename extensions can be considered as a type of metadata, though one of the most visible pieces of such information on modern computer systems.
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 and the extension limited to two or three characters; when a filename/filename extension combination was typed in commands, a period (.) was placed between the filename and filename extension.
  More results at FactBites »

 
 

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