Computer Basics

File Extensions

All files have extensions. The three letter combination following a dot or period in a filename. 

An extension tells your computer what program to use when opening the file. As an example, if you were in Word 97 and saved a file named 'letter', the program  would automatically add the extension '.doc'. You would end up with a file called 'letter.doc'. 

Each program you use, has its own file extension. There are literally thousands of file extensions used today.  Following are a few of the most common.  If there is one that is not listed and you would like to know what program to use to open it, please contact us and we would gladly add it to our list.

Questions about file extensions


Extension Description
.avi Video files. Mini clips.
.bat Batch file. Also similar to .exe files. As with .com files, this file extension is generally used for command programming. The frequently used file 'autoexec.bat' stores any pre Windows information, such as CD-ROM information.
.bmp Bitmap Picture file. Similar to jpg files, however, this file type tends to be rather large. If your intend on sending pictures over the internet, it would be wiser to save pictures in jpg formats as they are usually considerable smaller in size 
.com Command file. Similar to .exe files. More commonly used in DOS base programming. Your computer is started using the '' file.  If this file becomes damaged or is deleted, your computer will not start.   
.dll Dynamic Linking Library files. These files hold the connection or linking information between programs and hardware. It is advisable not to delete any of this kind of file unless you know it's function.
.doc Document file, most commonly used by the Word family of products.
.dot Word document template.. Templates are pre-defined documents, most commonly used for FAX forms, letterhead, membership forms, etc. 
.drv Driver files. These files hold the information about the devices or hardware your computer has.  This means, when you buy a printer, you must first tell your computer that it has a new part by installing it's drivers.  Only then can you print.
.exe Executable file. These files generally start programs. (i.e. word.exe starts the Word program.)  Not all .exe files can be opened by a user.  
.gif Picture file. Usually simple 16 color graphics. 
HyperText Markup files. File format used with the web. The internet uses  htm or html file formats.
.ico Icon files. The little pictures associated to programs, usually logos.
.inf Hardware information files. When loading different hardware, Windows frequently requires these kinds of files. 
.ini Information files. These files hold program information for your computer. The win.ini file holds information about programs loaded on your machine.
.jpg Picture file. High color resolution pictures, usually 256 ore more colors
.log Log files. These files document procedures used by your computer. For example, a file named 'install.log' would document the procedure taken to install any given program.
.mid Midi sound files. Usually longer, more elaborate files, such as musical pieces.
.mpg Audio/Video files. 
.pcx Another Picture format. Less efficient than jpg but better in size then bmp's
.pdf Adobe Acrobat Reader files.  
If your system is missing this program, you can get a copy of their free reader at
.ppt PowerPoint slide show. There is a viewer that can be downloaded from Microsoft, click here to get PowerPoint Viewer 97 
.sys System file. Again similar to the first three file types mentioned. Your computer can use a file named 'config.sys' which stores hardware information.
.txt Text file. Simply text files, usually discussing programs. Most program have a file named 'readme.txt', giving the user last minute information about the program they are dealing with.
.wav Wave sound files. Usually short sounds such a horns honking or doors closing.
.wpd WordPerfect document.
.wpt WordPerfect document template file. 
.xls Excel Spreadsheet document
.xlt Excel template.
.zip Zipped file. A file compression program, that reduces the size of files, allowing for speedier transfers over the net.



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