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"What Do Those Things Mean?"

(Image: .???)



At the end of most DOS and DOS-program file
names is a three-letter extension. Even since the
introduction of long file names, this has been generally
adhered to. This guide will sort out what each extension
represents and the purpose(s) for what the files might be used.

    While this guide is geared toward DOS users, many file extensions apply to other operating systems and their programs. However, be aware that some systems might also have different meanings and uses for the extension names given here.

    Audio/graphic formats and typical audio/graphic program extensions which are specific to such applications, are covered in DOS Audio & Graphic File Extensions. Font file types are also covered there, although some may be mentioned on here if one of those extensions is used for other purposes.

At the bottom of this webpage are links to
additional websites giving file name extensions
for other operating systems and their programs.
(Some of those sites also include DOS extensions).


DOS File Extension Guide

Direct-to-Section Access
Extensions Beginning with a
Non-Letter Character  

Extensions Beginning with...

A   B   C   D   E   F  

G   H   I   J   K   L  

M   N   O   P   Q   R  

S   T   U   V   W   X  

Y   Z  
Note that non-functioning letter-links indicate
there is no file here that currently
begins with that letter.

*    .@@@ - ?
    An MS-DOS identification file used by BACKUP and possibly other commands.

*    .$$$ - ?
    Used as a backup file name. Also used by EDLIN to designate an out-of-disc-space error condition, and by DOS for temporary work files, sometimes with different characters after the first dollar sign.

*    .!!! - ?
    Used as a temporary file by DOS.

*    .### - ?
    Used as a temporary file by DOS.


*    .all - ?
    Printer driver archive used by WordPerfect.

*    .ans - ANSI
    American National Standards Institute format.

*    .apm - Arachne Plug-In Module
    Used for Arachne Internet browser plug-ins.

*    .arc - Archive
    A compressed file consisting of a single large file or multiple files.

*    .arj - Archive Jung
    A Robert Jung compressed file consisting of a single large file or multiple files.

*    .ars - Audio Resource
    WordPerfect audio driver.

*    .asc - ASCII
    This is an ASCII (ASS-key) file. It is a plain-text standard and stands for "American Standard Code for Information Interchange".

*    .asm - Assembly Script ?, Assembler Source Module ?. Also Assembler or Assembly
    This file type contains a series of commands that become a computer program after being compiled into machine language.

*    .asp - Aspect
*    .asp - Association of Shareware Professionals

    Aspect is a script file containing a series of plain-English commands used by some programs to perform operations automatically. They may be generated by the program via a "record" feature or written by a user from scratch. The compiled script uses the .asx extention.

    The Association of Shareware Professionals uses the .asp extension.

*    .asx - Aspect Executable
    An assembled Aspect (.asp) script file.

*    .aux - Auxiliary
    A file that is a companion to one or more other files.


*    .bak - Backup
    Used by programs and users to make a copy of an existing file for safety and/or archive purposes.

*    .bas - Basic
    A basic computer-language program file.

*    .bat - Batch
    This extension is used to designate a batch file. Such a file is a series of commands in mostly plain English which perform an operation or series of operations in DOS. They come with some programs and may also be written by a user to make shortcuts or perform operations such as sorting or backups.

*    .bin - Binary
    A binary file.

*    .bit - ?
    A Lotus Manuscript file.

*    .bk or .bk! - Backup
    Used by programs and users to make a copy of an existing file for safety and/or archive purposes.

*    .bld - BASIC Load ?
    A BLOAD format for the BASIC computer language.

*    .btm - Batch, Memory
    A 4DOS batch file that is kept in memory. This speeds operations over a regular .bat file.


*    .c - C
    A file of programming language in the C format.

    Also a calendar file.

*    .cal - Calculate
    A calculator file used by some spreadsheet programs.

    Also a calendar file.

*    .cat - Catalog/Catalogue
    A master file used by MSBACKUP.

    May also be an inventory catalogue file used by some programs to list included files, or to list other products from the same authors/company.

*    .cbl - Cobol Language ?
    A file of programming language in the Cobol format.

*    .cfg - Configuration
    These files tell a program or DOS how to configure itself. That might mean what drivers to use, what files types to allow, how the program looks on the screen, etc. These may or may not be in plain text.

*    .cfn - Configuration ?
    Another type of configuration file.

*    .chk - Check Disk
    This is used by DOS' CHKDSK command to store lost file allocation units. Each file fragment is converted to a .chk file and numbered beginning with FILE0000.chk.

*    .chp - Chapter
    A file type used by Ventura Publisher.

*    .clp - Clip
    A file used to hold clipboard data. This changes as the user replaces saved text with newer text during the course of computer operations.

*    .cmp - Compress
    Compressed archive file used by Neosoft.

*    .cnf - Configuration
    These files tell a program or DOS how to configure itself. That might mean what drivers to use, what files types to allow, how the program looks on the screen, etc. These may or may not be in plain English.

*    .cob - Cobol
    A file of source code for the Cobol computer programming language.

*    .cod - Code
    An object code file for computer programming languages.

*    .com - Command
    These are small files under 64Kb (kilobytes) and are basic commands which come with most DOS programs. This extension is for compiled programs written by advanced DOS users. .com files perform specific operations (FORMAT or DISKCOPY), provide features (DOSKEY and MODE), or can also be drivers such as MOUSE.

*    .cpi - Code Page Information
    This is used by DOS to configure itself for non-English language use. Character sets are stored here, each with 256 characters.

*    .cpp - C++
    A file of programming language in the C++ format.

*    .cps - Central Point Software ?
    Used by Central Point for check list files in its anti-virus program.

*    .crf - Cross Reference
    A C++ crossreference file.

*    .crs - ? Resource
    A WordPerfect file.

*    .cvf - Compressed Volume File
    Used by Superstor and DoubleSpace to document a compressed drive's files.

*    .cvx - Convert ?
    Used by ConvertPerfect, a file conversion program for WordPerfect.


*    ._dd - Disk Doctor
    Used by Norton Utilities for file fragments located during disk diagnostic and repair operations by Disk Doctor. It saves the fragments in files with this extension.

*    .dat - Data
    Used to hold information about a particular aspect of a program or about a particular operation. The latter may update a .dat file to reflect recent changes. Other operations in the program may then view this file and other .dat files while determining a course of action. Many games programs use this extension for files that hold users' scores.

*    .db or .dbf - Data Base File
    These are used by data base programs to hold the users' information. Other programs may use them to hold information used by the application itself for such things as printer specifications regarding printer selection by the user.

*    .dbg - Debug
    Debug file.

*    .dbt - Data Base Text ?
    A data base file.

*    .dbv - Data Base, Variable
    A data base file that can vary its field size to accommodate text and other data, as required by its users.

*    .dcf - Driver Configuration File
    A Lotus 1-2-3 configuration file. The user selects the drivers required by 1-2-3 to interface with his or her display and printer. It also holds the user's country code.

*    .dct - Dictionary
    A dictionary file.

*    .ddt - ?
    A music file used by Epic MegaGames.

    It is used by some other software developers to designate data storage files.

*    .def - Definition

*    .dev - Device
    A device driver.

*    .dic - Dictionary
    A dictionary file.

*    .dif - Data Interchange Format
*    .dif - Differential Backup

    Data Interchange Format is used to exchange data among various programs and/or platforms (operating systems).

    Differential Backup is used by the MSBACKUP program.

*    .dir - Directory
    Used to house a directory list, especially for communications programs.

*    .dis - Description
    A text file containing a description of the associated software and/or a list of the files in the software package.

*    .diz - Description ?
    Appears to be used by most authors to declare a program's capabilities.

*    .dll - Dynamic Link Library
    Used by programs to supply information for various tasks. The information held in one file is shared among the various sub applications (modules).

    An example might be a .dll file which contains a set of icons which are common to all screen interfaces across an entire program. Each module would go to this file, as necessary, to display that icon. This saves each module from having to have a duplicate of the icons.

*    .doc - Document
    These can be ASCII (ASS-key) text files which often come with a program. They provide on-screen information about a program or its manufacturer. Being ASCII they may be read by any operating system platform.

    A second use is by Microsoft Word for data files made by the user. These are in MS Word code and cannot be read by all platforms, and sometimes not even by different versions of MS Word.

*    .dos - Disk Operating System
    Typically a text file with DOS specifications.

*    .dot - Document Template
    A template file used by MS Word.

*    .drs - Display Resource File
    Used by WordPerfect.

*    .drv - Driver
    These are the drivers used by programs to interface with a given system's hardware.

*    .dta - Data
    Used to hold information about a particular aspect of a program.

*    .dtf - Data Text Format?
    Used by Q&A for DOS.

*    .dtp - Datastorm Technologies Patch
    Used by Datastorm to designate a software patch file.

*    .dvp - DESQview Program?
    A DESQview configuration file, chiefly for the DOS programs that will be run under DESQview.


*    .eml - E-Mail
    An unofficial extension for an e-mail correspondence document. It may be in plain text or html. However, being unofficial, it could also be in a word processor format.

*    .err - Error
    Error file.

*    .exe - Executable
    As do .com, .bat and .btm files, these perform tasks but are typically larger in size. Major program files are executables, but utilities and other modules used by a program can also be in the .exe format.


*    .faq - Frequently Asked Questions
    These are ASCII (ASS-key) text files with program information, tips, how-to's, etc. They are laid out as a set of questions and answers.

*    .fil - File
    Typically, these are files in which a program stores a user's chosen information. As an example, ProComm Plus places snapshots of on-screen pages into SNAPShOT.fil whenever the user presses `Alt-g' (grab).

*    .fmt - Format
    Used to hold formatting information. Usally they hold the user's chosen layout for a particular document.

*    .fon - Phone or Font
    Keeps a phone directory or log of phone calls.

    Some softwares use this extension as a font file, but the common extension is ".fnt".

*    .for - FORTRAN
    A file of source code in the FORTRAN computer language.

*    .fox - FoxBASE
    A database file used by FoxPro.

*    .frm - Form
    Used for on-screen or printable forms. Often employed by programs for ordering purposes.

*    .fs - ?
    Used by Paradox.

*    .ful - Full
    An MSBACKUP catalogue file representing a full backup.

*    .fw and .fw2 - Framework
    Used by the Framework Office Suite versions 1 and 2.


*    .grb - Grab
    Used to designate a screen snapshot or "grab" file. Also used by MS-DOS DOSSHELL.

*    .grs - Graphic? Resource


*    .h, .hdr - Header
    Header file used by the `C' computer language; the latter extension is used by ProComm Plus.

*    .hex - Hexadecimal
    File in hexadecimal (Base 16) format.

*    .his - History
    This file type typically stores game scores or a user's changes to a program and/or its configuration. It may also be used to detail a program's evolution through various versions.

*    .hlp - Help
    These are used by a program to provide on-screen help. In some cases they are only in a form readable via the program itself. Otherwise, they will be plain text and may be looked at with any text file viewer.

*    .hnt - Hint
    Used by games programs.

*    .hst - History
    Used by software authors to show the progression of the versions of the program. Also used by on-line programs to track where the user has gone, and/or what he/she has done.

*    .htm - HTML (Hyper Text Mark-Up Language)
    These are the files of the Internet. They are ASCII (ASS-key), meaning they are in plain text and can be read by any computer system. Commands or "tags" are issued which tell an Internet browser how to display a page. Thus there are tags for font, bold, images, image placement, tables, etc.

*    .hyc - Hyphenation ?
    Used by WordPerfect for hyphenation lists.


*    .ice - ?
    A compressed file used by LHice.

*    .idx - Index
    An index file.

*    .inc - Incremental
    File format used by MSBACKUP.

*    .inf - Information
    Typically a text file which gives preliminary information about a program, its files, and the manufacturer or developer. It may also contain information required when an alternate configuration is selected for the program. This might occur under say, foreign language usage. .inf files are not to be confused with .pif files (program information file).

*    .ini - Initialisation
    Typically a text file which functions as a configuration for a given program. Often used by DOS multi-taskers and by older Windows versions to run a DOS program.

*    .ins - ?
    A list file used by WordPerfect to let it know in which directories certain files are kept which locations were changed by the user.

*    .inv - Invoice
    Used by company billing departments.

*    .irs - ? Resource File
    Used by WordPerfect.


*    .kbd - Keyboard
*    .key - Keyboard
    These are for alternate keyboard layouts or functions. They are used by programs which feature user-defined keyboard layouts.

    Also used for keyboard macros.


*    .lbl - Label
    Some programs store labels in a .lbl file.

*    .lbl - Library ?
    Used by dBASE library.

*    .lbr - Library
    Used by LU and similar programs that store multiple files in a single file, or archive. These archive files are generally not compressed.

*    .let - Letter
    Used by word processing programs.

*    .lex - Lexicon
    A WordPerfect dictionary file. This file extension is also used by the Prospect database program

*    .lha - LHARC
    A compressed file.

*    .lib - Library
    A library file holds information used by a program or routines for compilers.

*    .lic - License
    Software license agreement.

*    .log - Log
    A text file which holds information gathered after a particular operation, such as that associated with a disk checker or defragger program.

*    .lrs - Language? Resource
    Used by WordPerfect.

*    .lst - List
    Typically a text file which lists the files accompanying a program. A description of each file's purpose might be included.

    Some DOS users may employ the extension to designate lists of files upon which some action is to take place: "DEL @FILENAME.lst" instructs DOS to delete the files which are listed in a text file called "FILENAME.lst".

*    .ltr - Letter
    A letter file.

*    .lzh - ?
    A compressed archive file used by LHA.


*    .mac - Macros
    Files that are similar in purpose to batch files. They are used to automate procedures.

*    .mak - Make
    Used by programmers.

*    .man - Manual
    Text file with information about how to use a program.

*    .map - Map
    Map files typically hold directory tree information. Some games use this extension to designate the various playing fields.

    .map is also used by programmers as a linker file.

*    .mem - ?
    Used by dBASE.

*    .men - Menu
*    .meu - Menu

*    .mlb - Macro Library
    Used by Lotus 1-2-3.

*    .mmo - Memo
    A memorandum file. Usually brief in nature or a collection of memos.

*    .mnu - Menu
    A menu file. This may also be a mouse control file.

*    .mod - ?
    Use to support data exchange between DOS and Windows.

*    .mos - Mouse
    A mouse driver.

*    .mrs - Macro? Resource File
    A WordPerfect file format, possibly as a support for its macroing feature.

*    .msg - Message
    Typically used to hold prompts placed on screen by a program. Another usage is as a history file for on-screen messages.


*    .ndx - Index
    An index file. dBASE is one user.

*    .new - New
    A file, usually in text format, which spells out updates or bug fixes to a program.

*    .ng - Norton Guides
    A Norton database file.

*    .ntx - ?
    A dBASE or Prospect database index file.

*    .nws - News?
    Used by ProComm Plus.

*    .nuf - New User File
    A file that contains an on-screen message for when a user starts a program for the first time, or first logs on to a system. It is typically only ever displayed once.


*    .obj - Object
    A program intermediate object code file.

*    .old - Old
    Used to designate an older version of a file, typically for backup purposes.

*    .ovl - Overlay
*    .ovr - Overlay
    These are used by programs which do not fit within the old 640K (655,360 bytes) limit. Thus if you have a big spreadsheet, a large image, or any oversize files, they are placed in an overlay file and typically put into memory above 1 Mb.


*    .p - PASCAL
    A source code file for programmers.

*    .pad - Portable Application Description
    A file containing details about the accompanying software itself.

*    .pak - Pack or Packed
    A compressed file.

*    .pas - PASCAL
    A programming language file in the PASCAL format.

*    .pck - Package
    Used by programs for support information. As an example, EDIT-GM uses this file format to keep track of the files edited by the user and the line numbers on which changes have been made.
    Some DOS games also use this file format.

*    .pdf - Printer Defination File
    Used to define printer parameters.

*    .pdf - Public Document Format or Portable Document Format
    Cross-platform file format introduced by Adobe. Also may contain images.

*    .pdr - Printer Driver
    Used by Broderbund for printer drivers in programs such as Print Shop Deluxe.

*    .pdx - Paradox
    A spreadsheet file.

*    .pif - Program Information File
    Typically a text file used by task-switchers/multi-taskers. Each has the information on a given program being run by the multi-tasker. It would contain what is required by the program to run properly under the multi-tasker such as memory requirements, where that program's executable and data files reside, etc.

*    .pgm - Program
    An overlay file that is read into memory only when needed.

*    .pm4, .pm5 - Pagemaker
    Pagemaker formats.

*    .prd - Printer Driver
    Printer driver or definition file.

*    .prg - Program
    Used by dBASE.

    Used by programmers for source code.

*    .prm - Program
    Used by ProComm Plus.

*    .prn - Printer
    Printer driver or printer information file. Sometimes, it's a text file meant to be printed.

*    .prs - Printer Specification ?
    A printer definition file used by WordPerfect.

*    .prt - Printer Text?
    A printer manual.

*    .ps - PostScript
    A postscript program file.

*    .pst - Post
    An unofficial extension for saved Usenet or Internet forum posts. It may be in plain text or html. However, being unofficial, it might too, be in a word processor format.

*    .pw - PostScript
    Used by Professional Write.

*    .px - ?
    Used by Paradox.


*    .qa - Question Answer?
    Used by Q&A for DOS.

*    .qrs - ?
    Used by WordPerfect.

*    .qw - Qwery ?
    Used by Q&A for DOS.


*    .rec - Record
    A macro file containing the recorded steps for a given task. Also a file extension used by DOS' RECOVER for its salvaged files.

*    .reg - Registration
    A file, usually in text format, containing information (and sometimes the form) needed to register a shareware program.

*    .res - ?
    Used by some DOS games to keep track of users' scores.

*    .rft - Revisable Form Text
    Apparently used with a document regarding its content layout.

*    .rpt - Report
    A file generated after a particular operation to alert users as to what happened during that operation, and to advise of any problems or errors.

*    .rst - Restructured Text
    A text file that contains RST mark-up programming language code. It can be used to apply elementary formatting to text documents. Python uses it for program documentation and it can be used to make elementary web pages.

*    .rtf - Rich Text Format
    A form of text file which allows some formatting such as centering and bolding. It is typically used by word processing programs and is not compatible with plain .txt or plain .doc files.

*    .rtl - Run Time Library
    This is a support file shared among executables. It holds information common to them such as error messages. Norton utilities uses this format.

*    .rul - Rule
    Used by WordPerfect's speller.


*    .sam - ?
    Used by Ami-Pro.

*    .sav - Save
    Used by some programs to store information as to where a user goes or what files are accessed during the present session. Other programs simply use it to store various data or as a backup file. Game programs often hold the player's saved games in files with this extension.

.scr - Screen
    Used by ProComm Plus as its Screen Snapshot file.

*    .scr - Script
*    .srp - Script
    Scripts are plain-English files which are program or user generated. They perform a set of instructions as might be typed into the program, thus automating an operation, much as do batch or macro files.

*    .sdr - ?
    Used by PrintMaster as a name file.

*    .set - Settings or Setup
    Default or user-set parameters are stored in these files. MSBACKUP also uses this extension for settings files.

*    .sk - SideKick
    Utility format used by SideKick.

*    .sld - Slide
    These are files which contain information for slide-show graphics. They might have the commands for say, which slides to show, how long they remain on screen, delay between slides, etc.

*    .sty - Style
    Used by some word processors and desktop publishing programs to define the look of a document.

*    .sup - Supplementary
    A WordPerfect dictionary file holding supplementary words as entered by the user.

*    .swp - Swap
    This is used by task-switchers and multi-taskers. When a file is placed on to the hard drive because there is not enough memory, it may be given this extension, among others. The file is deleted when it is recovered from the hard drive unless an error has occurred.

*    .sty - Style
    WordPerfect style files.

*    .sys - System
    These can be drivers for things such as a RAM drive or a hardware device such as a mouse or printer. They may also be start-up files used by a program to get up and running.


*    .ths - Thesaurus
    WordPerfect thesaurus file.

*    .tmp - Temporary
    Used by operating systems, programs, and users to create a working file which is later to be discarded.

*    .tre - Tree
    WordPerfect keeps a drive's directory structure stored in here.

*    .tst - Test
    Usually a temporary file generated to check some parameter of a program or its operation.

*    .tut - Tutorial
    A teaching file.

*    .txt - Text
    These are ASCII (ASS-key) files which often come with a program. Like plain .doc files, they provide on-screen information about a program or its manufacturer and often contain a program's "Help" guide. Being ASCII they may be read by any operating system platform.

    A second use is by word processor users that wish to save a file in plain text. Instead of the .doc extension, .txt is used so as to allow the file to be opened by other word processors and text editors.


*    .umb - ? MEMMAKER Backup ?
    Used by Microsoft's MEMMAKER for backup.

*    .upd - Updates
    A text file containing a program's history log of changes, corrections and updates.

*    .usr - User
    A file that stores user information such as name, password, ability level...


*    .vbm- Veeam Backup Metadata
    Used by Veeam for its backup and replication software.

*    .vbx - Visual Basic ?
    A control file.

*    .vrs - Video Resource
    WordPerfect graphic screen driver, and/or monitor information file.

*    .vwr - Viewer
    CP Tools file viewer.


*    .wcm - ?
    Used by Microsoft Works.

*    .wdb - Works Database
    Used by Microsoft Works.

*    .win - Winner
    Used by some game programs to keep track of high scores.

*    .wk - Work
    Typically used by spreadsheet programs. Different companies add another character to this extension. Thus, .wks, .wk1, .wk3, .wk4 and .wk5 are used by Lotus for its 1-2-3 spreadsheets and for Charts; .wke for its educational worksheet files. Quattro uses .wk2 and .wkq.

*    .wki - ?
    Used by Lotus 1-2-3 Charts.

*    .wkq - ?
    Used by QuattroPro.

*    .wks - Worksheet
    Typically used by spreadsheet programs, but also by Microsoft Works.

*    .wku - ?
    Used by Lotus 1-2-3 Charts.

*    .wpd - WordPerfect Demo
    Used by WordPerfect for its demonstration files.

*    .wpk - WordPerfect Keyboard
    A WordPerfect keyboard file.

*    .wpm - WordPerfect Macro
    Files used by WordPerfect used to automate procedures. Users may compose their own, as well.

*    .wps - Word Processing ?
    Used by Microsoft Works' word processor, and by WordPerfect spelling files.

*    .wq1 wq2 - Work Quattro
    Used by Quattro for its Quattro Pro spreadsheet files. The number translates to a program version. `1' is Version One and may be compatible with versions through 4.x. `2' represents Version Five.

*    .wrk - Work
    Worksheet file used by Lotus Symphony.

*    .ws - WordStar
    Also: .ws1, .ws2, and .ws3. All are used by WordStar and WordStar 2000.


*    .xlm - Excel Macro
    Used by the Excel spreadsheet for its macros. These files are used to automate procedures.

*    .xls - Excel Spreadsheet
    Used by the Excel spreadsheet for its spreadsheet files.

*    .xlt - Translation Table
    Used by ProComm Plus.

*    .xpl - ? Programming Language
    A programming language based on PL/I, of which the latter was originally for designers of business, engineering, scientific, and system softwares.

*    .xtp - Xtree ?
    An overlay files used by Xtree.


*    .zip - Zip
    These are compressed files, typically made by PKZIP, but others use this extension if they are compatible with PKZIP. Files contained in the .zip file can be any type, but are usually data files. They are compressed in order to reduce their size for storage, or for transmission over the Internet or an internal network. .zip files may also be used to combine multiple files into one handy file. This makes it ideal for archiving. Later, any or all of the individual files may be restored via PKUNZIP or other programs that recognise the .zip format.

*    .zoo - ?
    A compressed archive.

    Here are additional websites dedicated to file extensions:

Go to
DOS Audio/Graphic
File Extensions

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