These extensions at the end of a file name refer to the type of file it is. This information is used by your operating system to launch an appropriate program when you click on the file name. Example: file.txt is a text file and can be opened by a text editor program.

.$$$	Temporary file
.2GR	A file that allows Windows to display text and graphics in standard mode on a 286 or 386 computer (filename extension).
.386	Swap file; enables computer running in enhanced mode to use Windows with virtual memory (filename extension).
.3GR	A file that allows Windows to display text and graphics in enhanced mode on a 386, 486, or Pentium computer (filename extension).
.906	Calcomp plotter
.A3W	MacroMedia Authorware Windows 3.5 (filename extension).
.ABK	AutoBackup, Corel Draw (filename extension).
.ABR	Brush – Adobe Photoshop (filename extension).
.ACL	Keyboard accelerator, Corel Draw 6 (filename extension).
.ACM	Windows system directory file (filename extension).
.ACV	Drivers for compressing or decompressing audio files, OS/2 (filename extension).
.AD	After Dark
.ADB	1. Appointment DataBase, HP 100LX (filename extension). 2. Body file type, Ada language (filename extension).
.ADD	Adapter Driver – OS/2 (filename extension).
.ADM	AfterDark MultiModule (filename extension).
.ADR	AfterDark Randomizer (filename extension). AfterDark is a screensaver program that can be set to randomly display a variety of screensaver patterns one after another.
.ADS	Specification file type, Ada language (filename extension).
.AFM	Adobe Font Metrics – Type 1 font metrics (filename extension).
.AG4	Access G4
.AI	Adobe Illustrator
.AIF	Audio Interchange File Format or AIFF (filename extension). A format developed by Apple Computer for storing high-quality sampled audio and musical instrument information. It can be played on PC and Mac.
.aiff	Audio Interchange File Format. An uncompressed sound format developed by Apple Computer for storing high-quality sampled audio and musical instrument information. It can be played on PC and Mac, using QuickTime or Sound Player.
.ALL	Arts and Letters Library (filename extension).
.ANI	Animated cursor (filename extension).
.ANS	ANSI text (filename extension).
.API	Application Program Interface (filename extension). An interface between the operating system and application programs.
.APP	MacroMedia Authorware package (filename extension).
.ARC	ARC or ARC+ compressed
.arj	A PC compressed format found on European sites (filename extension), which can be decoded with unArjMac, DeArj, and SITEX10.EXE (win).
.ART	An art file, in some draw or paint applications (filename extension).
.ASC	ASCII text file
.ASF	Active Streaming File – HoTMetaL Pro (filename extension).
.ASM	Assembly Source Code
.ASP	Active Server Page – Microsoft (filename extension).
.AST	Assistant file – Claris Works (filename extension). Assistants guide the user through a task by asking a series of questions and then use the answers to perform a task. Assistants in Claris Works can be used to create such useful items as calendars, newsletters, stationery, labels, and address lists, to make footnotes within a file, to find documents, etc.
.ATT	AT&T
.AU	A sound file format used on Sun Microsystems or other UNIX computers
.AVI	AVI movie format
.AVS	Intel video capture format (filename extension).
.b64	Base 64 (filename extension), the encoding format used by the Multipurpose Internet Mail Extension.
.BAK	Backup copy in DOS or OS/2
.BAS	BASIC program file
.BAT	Batch
.BFC	Briefcase document – Windows 95 (filename extension).
.BG	Backgammon game (filename extension).
.BI	Binary file (filename extension).
.BIN	Driver
.bin	A MacBinary II encoded file (filename extension). This file type, downloaded as MacBinary or Binary, can be decompressed with Stuffit Expander.
.BK	Backup copy
.BK$	Backup file (filename extension).
.BLT	Wordperfect for DOS (filename extension).
.BMP	Bitmap
.BNK	Sim City game file (filename extension).
.BRX	Browse Index (filename extension). Found on multimedia CD-ROMs.
.BTM	Batch file – Norton Utilities (filename extension).
.C	C program file
.CAB	Microsoft compressed format
.CAL	Calendar or CALS
.CAP	Caption
.CBT	Computer-Based Training; a tutorial file (filename extension).
.CCH	Corel chart (filename extension).
.CCM	Lotus cc:Mail (filename extension).
.CDA	CD Audio track (filename extension).
.CDR	CorelDraw
.CDT	Corel Draw template (filename extension).
.CDX	Corel Draw compressed file (file extension).
.CDX	Visual FoxPro database index (filename extension).
.CFB	Compton’s multimedia encyclopedia (filename extension).
.CFG	Configuration
.CFL	Corel Flow (filename extension).
.CGI	Common Gateway Interface (filename extension). A file that makes it possible for HTTP servers to interface with computer programs to provide interactive functions like fill-out forms.
.CGM	CGM graphics
.CHK	Checkdisk – DOS
.CHP	Chapter – Ventura
.CIF	Chapter Information – Venture
.CIM	Sim City file (filename extension).
.CIT	Intergraph scanned image
.CLP	Clipboard
.CMD	Command file — OS/2
.CMF	Corel MetaFile (filename extension).
.CMF	SoundBlaster file (filename extension).
.CMP	LEAD Technologies graphics
.CMV	Corel Move animation (filename extension).
.CNF	Configuration file (filename extension).
.CNQ	Compuworks Design Shop (filename extension).
.COB	COBOL source code
.COM	Command file – small version of .EXE
.CPE	Fax Cover document (filename extension).
.CPI	Code Page – DOS
.CPL	Control Panel – Windows
.CPP	C++ program file
.CPR	Knowledge Access graphics
.CPT	Compact Pro
.CPX	Corel Presentation Exchange compressed file (filename extension).
.CRD	Windows Cardfile (filename extension).
.CSC	Corel Script (filename extension).
.CSS	Cascading Style Sheet (filename extension).
.CSV	Comma delimited
.CTL	Control file (filename extension).
.CTY	City file – SimCity (filename extension).
.CUR	Windows cursor image
.CUT	Dr. Halo graphics
.CV	Microsoft CodeView (filename extension).
.CWK	Claris Works (filename extension).
.CWS	Claris Works template (filename extension).
.DAT	Data
.DB	Table – Paradox
.DBC	Visual FoxPro database (filename extension).
.DBF	Database File – dBASE
.DBT	Database text – dBASE
.DBX	DATABEAM graphics
.DCA	IBM text
.DCS	Color Separation – EPS
.DCT	Dictionary
.DD	Disk Doubler
.DDI	Disk Doubler Image (filename extension).
.DEF	Definition – C++ (filename extension).
.DER	Certificate (filename extension).
.DEV	Device driver file (filename extension).
.DG	Autotrol graphics
.DGN	Intergraph graphics
.DIB	DIB graphics – Windows
.DIC	Dictionary
.DIF	Data Interchange Format spreadsheet
.DLL	Dynamic link library
.DOC	Document file
.DOT	Document Template – Microsoft Word (filename extension).
.DOX	MultiMate document
.DPI	Dots Per Inch – graphics
.DPR	Delphi project file (filename extension).
.DRV	Driver
.DRW	Designer graphics
.DS4	Designer graphics, version 4
.DSF	Designer graphics, version 6
.DWG	AutoCAD vector format
.DWG	Drawing – AutoCAD (filename extension).
.DX	Document Imaging
.DXF	AutoCAD vector format
.ED5	EDMICS graphics
.EMF	Enhanced Windows Metafile (filename extension).
.eml	electronic mail
.enc	encoded
.EPS	Encapsulated PostScript format
.ESI	Esri plot file
.EXE	Executable file — machine code
.FAX	Fax
.FDX	Force Index
.FH3	Aldus Freehand 3 (filename extension).
.FLC	AutoDesk animation
.FLD	Thumbnail folder – Hijaak
.FLI	AutoDesk animation
.FLR	Live3D (filename extension).
.FLT	Filter – graphics conversion
.FM	Framemaker (filename extension).
.FM3	Format for 1-2-3 Version 3
.FMT	Format – dBASE
.FNT	Font
.FOG	Fontographer font (filename extension).
.FON	1. Bitmapped Font – Windows 2. Phone
.FOR	FORTRAN
.FOT	Windows TrueType font
.FOX	FoxBase
.FP	Claris FileMaker Pro (filename extension).
.FP1	Flying Pigs (filename extension).
.FP3	Filemaker Pro 3
.FPX	FlashPix bitmap (filename extension).
.FRM	Form design — Visual Basic
.FRS	WordPerfect Graphics Driver
.G4	GTX RasterCAD
.GCA	GOCA graphics
.GED	Arts & Letters graphics
.GEM	GEM graphics
.GEO	VideoScope (filename extension).
.GIF	Graphics Interchange Format
.GLY	Glossary
.GP3	CCITT compressed Group 3 TIFF file (filename extension).
.GP4	Group 4 – CALS, ITU (filename extension). CCITT compressed Group 4 TIFF file.
.GRA	Microsoft Graph (filename extension).
.GRF	Graph
.GRP	Group
.GX1	Show Partner graphics
.GX2	Show Partner graphics
.GZ	GNU gzip compressed file – Unix
.H	Header (filename extension — C).
.HDF	Hierarchical Data File
.HED	HighEdit document (filename extension).
.HEL	Microsoft Hellbender game file (filename extension).
.HGL	HP Graphics Language (filename extension).
.HLP	Help
.HPJ	Help Project – Visual Basic (filename extension).
.HPL	HP Graphics
.HQX	BinHex (filename extension — Macintosh).
.HST	Host
.HT	HyperTerminal (filename extension).
.htm	DOS filename extension for a document with HTML coding, which can be read by WWW browsers.
.html	Filename extension for a document with HTML coding, which can be read by WWW browsers.
.HWP	Hangul Word Processor (filename extension).
.HYC	Hyphenation – WordPerfect
.HYP	Hyphenation
.ICA	IOCA graphics
.ICB	Targa bitmap (filename extension).
.ICM	Image Colour Matching (filename extension).
.ICO	Icon – Windows or OS/2
.ICON	Sun icon and cursor
.IDD	Instrument Definition – MIDI (filename extension).
.IDE	Integrated Development Environment configuration (filename extension)
.IDX	Index
.IFF	Amiga
.IGF	Inset Systems graphics – Hijaak
.IIF	Interchange File – QuickBooks for Windows (filename extension).
.IL	Icon Library
.ima	Winimage compressed format These files can be decoded or mounted by ShrinkWrap.
.image	Mac disk image (filename extension); a compressed format which can be decoded or mounted by DiskCopy, Disk Image Mounter, Disk Charmer, and ShrinkWrap (ImageMaster).
.IMG	Image. This file is a Macintosh Disk Image. Disk Copy can be used to mount the disk image on the Macintosh desktop. The mounted disk image will behave like a read-only disk.
.IND	Index
.INF	Information
.INI	Initialization – configuration settings
.IOB	Imagine file (filename extension).
.ISU	Netscape file (filename extension).
.IT	MOD music file format (filename extension).
.IW	Idlewild screensaver (filename extension).
.IX	Index File – Framemaker (filename extension).
.JFF or .JFIF	JPEG File Interchange Format; a 24-bit graphic format. It can be opened with QuickTime, a WWW browser, or a graphics viewer such as JPEGView.
.JIF	JPEG Image Format (filename extension).
.JPEG	JPEG bitmap (filename extension).
.JPG	file extension for JPEG (Joint Photographic Experts Group). A file stored in JPEG format. JPEG,an ISO/ITU standard for storing images with high compression capability, uses a discreet cosine transform that can achieve compression rates of 100:1 (significant loss of data from original) and 20:1 (minimal loss). C-Cube Microsystems introduced the first JPEG chip.
.JT	JT Fax
.JTF	JPEG bitmap (filename extension).
.KDC	Kodak Photo-Enhancer (filename extension).
.KFX	Kofax
.LBL	Label – dBASE
.LBM	Deluxe Paint graphics file
.LDB	Lock file – Microsoft Access (filename extension).
.LEG	Legacy document (filename extension).
.lha	Filename extension for a PC/Amiga compression format decodable by LHA Expander or MacLHA.
.lhs	Literate Haskell source file
.lhz	LHA compression file
.LIB	Library
.LIC	License file – shareware (filename extension).
.LOG	Log
.LST	List (filename extension).
.LWP	Lotus Word Pro document (filename extension).
.LZH	LHARC compression
.lzs	PC/Amiga compression format
.M3D	Motion 3D – Corel (filename extension).
.MAC	MacPaint
.MAF	Microsoft Access Form (filename extension).
.MAK	Makefile
.MAM	Microsoft Access Macro (filename extension).
.MAP	Map – linkage editor
.MAQ	Microsoft Access Query (filename extension).
.MAR	Microsoft Access Report (filename extension).
.MAT	Microsoft Access Table (filename extension).
.MCS	MathCAD format
.MCW	Microsoft Word for Macintosh (filename extension).
.MDB	Access database
.MDX	Multi-index
.MET	Metafile – OS/2
.MEU	Menu
.MFF	MIDI File Format (filename extension).
.MGF	Micrografx Draw Font (filename extension).
.MI	Miscellaneous (filename extension).
.MIC	Microsoft Image Composer (filename extension).
.MID	MIDI

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