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File Types


Computers only understand information in the form of 1s and 0s. When you create a computer file, you are storing all of your information in the form of 1s and 0s in such a way that it can be converted back into something meaningful. This process is called "encoding."

Your file is encoded in a fashion appropriate to the kind of information that it represents. Microsoft Word documents are encoded differently from image files, both of which are different from video or sound files. The type of encoding is the file format.


File Names and Extensions

File names include information in them that tells the computer how to interpret the encoded data. That information is passed in the extension of the file name. The extension is attached to the file name with a dot (for example, .doc, .pdf, .jpg). The extension indicates the file format and what programs can open it. Below, you'll find a list of the most common file types.

Occasionally files are saved without the proper extension. This is more common on Macs as Mac files have other ways of encoding file format information. But it does cause trouble for PCs. If you receive a file you can't open because there is no extension, you may be able to fix the file by adding the extension. You will need to know what kind of file you have received. You can find this out by making an educated guess or asking the sender. Once you know what kind of a file you have:

  • Click the name of the file twice to select.
  • Add a dot and then the proper extension.
  • Your computer will probably ask you to confirm the change; select OK.


Extension Name Usage
ai Adobe Illustrator Vector-based image which is native to and can only be opened by Illustrator.
bmp Bitmap Image file that is native to PCs. Macs can usually open these, but not always!
doc Microsoft Word Document (pre-2007) Format of the popular word processor Microsoft Word. Preserves sophisticated formatting of written documents. Because of its popularity, some other word processors can also create doc files.
docx Microsoft Word Document (post-2007) Introduced in recent versions of Microsoft Word, this is similar to the doc format. A converter exists to open this file type with some earlier versions of Word.
eps Encapsulated PostScript A file format used in typesetting and desktop publishing. Preserves layout and is easily transfered from one machine to another. Used in printing.
gif Graphical Interface Format Great for simple images that feature flat color. Works well in the Class Discusssion.
htm Hypertext Markup Language A basic web page viewable in any browser. This is the default extension for PCs, but, like html, it is cross-platform.
html Hypertext Markup Language A basic web page viewable in any browser. This is the default extension for Macs, but, like htm, it is cross-platform.
jpg/jpeg Joint Photographic Experts Group Great for images with lots of detail and color transitions, such as photographs and scans. Works well in the Class Discussion.
mov QuickTime Movie Audio/video format from Apple. Cross-platform with the QuickTime player.
mp3/MPEG-3 Moving Picture Expert Group Audio file that can be played on the web or by iTunes or any other MP3 program/player.
mp4/MPEG-4 Moving Picture Expert Group Audio/video format with excellent video compression. Plays in browsers and stand-alone video players.
obj Object File format used by 3D graphics applications. Developed by Wavefront Technologies.
pdf Portable Document File Excellent file type for reports where layout is important. Preserves typefaces, layout, and images. Requires free Adobe Acrobat Reader.
png Portable Network Graphic Image that offers good compression without loss of data and details. Great for all types of images. May not work in all browsers, but will display in the Class Discussion with a compatible browser.
ppt Microsoft PowerPoint Slideshow format commonly used for presentations.
psd Adobe Photoshop Document

Native to Adobe Photoshop but can also be opened by certain other image-editing programs.

rtf Rich Format Text Preserves text formatting of written documents. Originally developed by Microsoft, it is a cross platform altenative to Word's doc format.
rm Real Media Audio/video format playable in RealPlayer.
sit/sitx StuffIt
Used to archive folders and files. Compresses and protects the files for uploading and downloading.
svg Scalable Vector Graphics Open standard XML-based language vector image format for the web. Can be animated and is supported by most modern browsers.
swf Small Web Format Provides animation, video, audio and interactivity on the web. Requires the free Flash Player.
tif/tiff Tagged Image FIle Format High-quality bitmap image file type, mostly used in print. Can be read on both PCs and Macs. These files are big!
txt Plain text Used for text only documents with no formatting.
xls Microsoft Excel Speadsheet format used to create tables and other charts.
zip Zip Used by programs such as WinZip to archive both individual files and folders full of files. Great for transferring multiple files at once. Reduces file/folder size. Helps protect the enclosed files from corruption.