Standard ﬁle extensions following the names of ﬁles can indicate whether a particular ﬁle is a program or data ﬁle. If it is a data ﬁle, the extension can indicate the application category that might be used to edit the ﬁle. Many common ﬁle extensions are three characters long, although there is no longer a strict character limit for the ﬁle name or extension in most modern operating systems. A period separates the extension from the ﬁle name itself.
Figure: File extensions.
Common File Extensions
The following table lists a number of common ﬁle extensions. Because Windows uses the ﬁle extension to determine how the system will use a ﬁle, if you alter a ﬁle name extension, you might ﬁnd that a program ﬁle will not execute properly or that a data ﬁle will not automatically open in the associated application.
File Extension and Description
.txt – A plain text ﬁle containing no formatting. Can be opened in any text editing program, such as Notepad, or word processing programs, such as Microsoft®Word.
.rtf – Rich Text Format, a text ﬁle that can include a limited amount of formatting such as bold and italic. Can be opened in various applications such as common word processors or Microsoft’s WordPad accessory.
.doc – A data ﬁle created in a word-processing program such as Microsoft Word or WordPad. You might also see .docx, an Office 2010 format.
.bat – A batch ﬁle; a small text ﬁle containing a list of system commands that execute in a “batch” rather than requiring the user to type each one in succession.
.bin – A binary ﬁle, containing only binary data (1s and 0s), which cannot typically be opened and read by a user application.
.com – A command ﬁle or compiled application ﬁle.
.exe – Executable ﬁles that launch programs and applications.
.dll – A Dynamic Link Library ﬁle, containing additional application settings or functions that are loaded by executable ﬁles as needed.
.hlp, .chm – Help ﬁles used by various applications.
.htm, .html – HyperText Markup Language (HTML) ﬁles, used to create webpages.
.inf – Setup conﬁguration settings for operating systems and applications.
.ini – Conﬁguration settings for software and hardware components.
.msi – A Windows Installer package; a ﬁle that can specify installation parameters for an application.
.sys – System ﬁles. System ﬁles are typically hidden, as their deletion can prevent the computer from working properly. With system ﬁles, it is not just the extension that is important because it helps the computer recognize it as a system ﬁle, but the location as well.
.tif, .jpg, .jpeg, .gif, – Graphic image ﬁles in various formats.
.bmp, .png , .xls, .ppt, .mdb – Data ﬁles created in Microsoft®Excel®, Microsoft®PowerPoint®, and Microsoft®Access™, respectively. Office 2007 and Office 2010 allow for .xlsx, .pptx, and .mdbx ﬁles.
Viewing File Extensions
How You Do It
1. Open the folder containing the Windows system files.
a. Choose Start→Computer.
b. Double-click the C drive.
c. Double-click the Windows folder.
2. Display the file extensions.
a. On the menu bar, choose Organize→Folder and search options.
b. Select the View tab.
c. Uncheck Hide extensions for known file types and click OK.
3. Examine the file extensions.
a. Scroll down to view the files.
b. The first few files in the window have a number of different extensions.
c. To see all the files in a list format, right-click in an open area and choose View→List.
d. To see similar extensions grouped together, right-click in an open area and choose Sort by→Type.
e. To return to the default view, right-click in an open area and choose Sort by→Name.
f. Close the window.