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File Extensions

What Are File Extensions?

SUMMARY: File extensions defined. This tip explains what the usually three characters are for.

In general terms, a file format in the PC world signifies what type of information is containing in a particular file. These are usually designated by the one to four (usually three) characters (the extensions) after the period in a filename. For example:

Filename: readme.txt
The "txt" designates the file format of this particular file, a plain-text file.

Filename: game.exe
The "exe" designates the file format of this particular file, an executable file.

Note that file extensions do not always signify the type of information inside a file; sometimes programmers hide the type of content inside a file with fake extensions. Also, some filenames may have multiple file extensions that can trick you into opening a Trojan Horse. However, this is a Windows tweak that can help you find files with multiple extensions.

More information about these and other particular file type can be found in this section's tips on MalekTips.

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The MalekTips website was created in 1998 by Andrew Malek of Envision Programming. The page's goal is to freely disperse computer-related tips, hints, and informative articles. Tips are organized to be easy to find, and are presented clearly, in easy-to-understand language. MalekTips also provides information and links to public-domain, open source, freeware, shareware, and commercial software available for download.