A different view

Suddenly you see files you didn’t see before. Those new files are system files. Windows by default hides system files from you to avoid them being deleted by accident because that could seriously mess up the operating system up to the point where you cannot boot anymore and have to reinstall Windows.

Another thing you should notice is that almost every file now has a dot after the file name followed by three more letters. That is called a file extension. These extensions make it a lot easier to identify a file, see what type of file it is, what it does, and what program it is associated with. The following table shows a list of the most common file extensions and explains what they mean:

ExtensionWhat it means
aviVideo clip – A type of video file format
bakBackup – When a program makes changes to an important file, it should make a backup first. Bak is a common extension to indicate a backup file
bmpBitmap – A type of graphics file containing an image
cabCabinet – An archive file containing compressed files, usually used by installation programs to store compressed setup files
dllDynamic Link Library – A critical file to Windows and applications. It stores additional commands and information for applications that are called from the program as needed. If a dll file is deleted, the program probably will not work anymore and needs to be reinstalled
docDocument – A Microsoft Word document
exeExecutable – This file is an actual application that can be launched. For example, Notepad.exe contains the Windows Notepad application
gifGraphics Interchange Format – A type of graphics file containing an image
hlpHelp – This is where Windows and applications store the information that you get when you access the Help menu
htmlHyper Text Markup Language – one of the several languages used to create documents for the Internet
icoIcon – The little pictures next to filenames or on your desktop are sometimes stored in this type of file
infSetup Information – This file type comes with most applications and drivers. It contains information that Windows needs to install that application or driver
iniInitialization file – Windows as well as most applications store some configuration settings, e.g. user preferences, in ini files. If such a file is deleted, the program probably will still work, but all custom settings are lost
jpg/jpegJoint Photographic Experts Group – A type of graphics file containing an image
logLog – Some applications keep track of certain activity, it is stored in a log file
mid/midiMusical Instrument Digital Interface – A music industry standard for electronic forms of music
mp3Moving Picture Experts Group Audio Layer 3 – Compressed audio file
mpg/mpegMoving Picture Experts Group – A type of digital compression standard
pdfPortable Document Format – A cross-platform file format developed by Adobe
tifTagged Image Format – A type of graphics file containing an image
tmpTemporary file – A lot of times Windows or other applications will save some information temporarily on the hard drive. Normally those files are supposed to be deleted when they’re no longer needed, but sometimes they remain. Usually these files can be removed
txtText – This indicates a plain ASCII text file that can be read by pretty much every word processing application
wavWave – Another type of sound file
zipZip – An archive file storing compressed files

If you want to know about other file extensions you didn’t see listed here, check out http://www.webopedia.com where you can search for file extensions and many other computer related terms.

Now that you have an idea what file extensions are and can identify the most popular ones, let’s take a closer look at what those extensions are good for.


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