| .$$$ | 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). |