Extending Your File Extension Knowledge

Contributed by Jay Schroyer

When you save a file to your computer, you’re always looking for a clever, space-saving title that will help you relocate the file the next time you want to access it. Some are as mundane as “Joe’s 2007 Budget” or “Current Phone List.”

Computer users didn’t always have the luxury of naming their files with obvious and lengthy titles. Earlier operating systems limited the number of characters that a file could utilize for naming to eight. So Joe’s budget might end up being “07JoeBud” and the phone list would become “CurrPhon.” Not exactly the most intuitive titles especially if you have multiple editions of the same file.

One thing that files have always had from the early days of computers up to modern times is the use of file extensions. File extensions are those mysterious three letters that appear after the period of each file that you name.

These extensions are exclusive to the program that has created the saved file and can sometimes contain only two letters (the Adobe® Illustrator® “.ai”) or four letters (Windows video file “.mpeg”) instead of the standard three. Even producers of shareware and independent software will create programs that use their own extensions and leave you scratching your head as to what type of file it is since it is not commonly known or used.

Also, within a programs file extension designation, there are slight differences that identify different kinds of files within that program. For example, Excel® files are saved as “.xl,” but if it’s a chart it is saved as “.xlc” and a macro as “.xlm.” Knowing what a files extension means can help you in a few ways.

Opening Files Extensions are also used by your computer to identify files and to determine which programs will be used to access this file. It’s possible that you’ve downloaded an image file before without an extension whose icon shows up as unidentifiable (usually a white square with a blue top and colored dots below). When you’ve double-clicked on it, the computer may have asked you what program to use to open it or it may have tried the default program and told you that it couldn’t.

This is because the computer isn’t sure what kind of file this is. If you right-click on it and choose “Rename,” you can add the extension “.jpg” to it and your computer will suddenly produce a thumbnail of it and allow you to open it in the Fax and Picture Viewer.

If you don’t have the program that created a file that you received, the computer will recommend or ask you to choose a program to open the unidentifiable file with, but if you choose a program that isn’t compatible with the file, you will receive an error and the file will not open.

Knowing your extensions can prevent you from wasting a lot of time trying to open a file that you just don’t have the program to open it with.

Compatibility By knowing your file extensions, you can very quickly tell if you have the software to open a file that someone sends you. A lot of files that are shared nowadays are PDFs, or Portable Document Format, because as long as the receiver has at least the Adobe® Acrobat® Reader® they can be accessed.

This format (PDF) is fine for sharing as long as the receiver isn’t expected to edit the document. For extensive revisions and changes, nothing will ever replace the original format of the file. So if you know how to read the file extension, you can very quickly learn that the “.ppt” file that someone just sent you won’t open in anything less than Microsoft® PowerPoint®.

Viruses As anti-virus software and computer firewalls become smarter and stronger, hackers and data miners must also evolve to take advantage of unwitting computer users. Some hackers have taken to naming virus files with commonly used extensions and effectively fooling receivers of their viruses into opening them and infecting their machine.

By knowing your extensions, you can make an educated guess as to whether an e-mail attachment you are receiving is legitimate or not. You may need to change some settings on your computer as Windows has a feature that will actually allow you to view files without their extensions listed.

It’s good advice to turn this feature on because it will give you more information about files that people are sending you. You can find this in the “Folder Options” under the “Control Panel.” If someone sends you a bogus “.exe” file and your computer isn’t showing you that it’s an executable file, you may unknowingly open it and begin an installation of a malicious program that will eat your computers hard drive from the inside out.

Common File Extensions Here are some commonly used file extensions that you may run into during your computer usage. This is by no means a comprehensive list, but they are common ones. Remember, there is a plentitude of resources online that offer alphabetical and searchable databases of file extensions if you ever get stuck, but if you can learn the basic Microsoft extensions for Word, Works, FrontPage®, Money, Quicken®, Excel®, and even Publisher, you’ll be that much further ahead when it comes to sharing files and protecting your computer.

• Microsoft® Products: Word (.doc), Excel® (.xl), PowerPoint® (.ppt), Publisher (.pub), Works (.wks), Money (.mny), Front Page (.fwp), Quicken® (.qdf), Access™ (.ade)



• Adobe® Products: Photoshop® (.psd), Illustrator® (.ai), Acrobat® (.pdf)



• Audio/Visual: graphics (.png, .jpg, .gif, .tiff), MIDI (.midi), wave file (.wav), Quicktime® movie (.mov), Windows® media player movie (.mpeg), music files (.mp2, .mp3, .mp4)



• System Files: executable files/programs (.exe), postscript or printer language (.ps)

Adobe, Photoshop, Acrobat, Reader, and Illustrator are trademarks or registered trademarks of Adobe Systems Incorporated in the U.S. and/or other countries. Microsoft, PowerPoint, FrontPage, Excel, and Windows are trademarks or registered trademarks of Microsoft Corporation in the U.S. and/or other countries. Quicktime is a registered trademark of Apple Computer, Inc., registered in the U.S. and/or other countries. Quicken is a trademark of Intuit Inc., registered in the U.S. and/or other countries.

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