A CDE Definition
(DATa file) A file that uses the .DAT extension. It is widely used for a variety of data content. See extension.
(1) See domain extension.
(2) A software add-on. For example, extensions add functionality to Firefox and Chrome Web browsers.
(3) Prior to Mac OS X, an executable module that enhanced the Mac operating system. The Windows counterpart is a "dynamic link library" (see DLL).
(4) Enhancements to Apple's iOS 8 and OS X Version 10.10 that enable apps to share functions in other apps. See "iOS 8" in iOS versions.
(5) A file type that is appended to the end of a file name. All executable programs in the Windows and Mac worlds use extensions: .EXE in Windows; .APP in Mac (see APP file). In the Unix/Linux environment, "executables" do not use an extension, but no matter which environment, "data" files have extensions. For example, a file with a .DOC or .DOCX extension is a Microsoft Word document. A file with a .JPG extension is a JPEG image.
Prior to Windows 95, extensions were limited to three characters. Starting with Windows 95, they can be very large (254-260 characters depending on Windows version); however, they are kept small in practice.
Common Extensions and Exhaustive Lists
In this encyclopedia, more than 500 common file extensions are listed under the terms "extension," followed by their first letter such as extension a, extension b and extension c. However, there are websites that catalog many more, including the most obscure; for example, visit www.filext.com. See Win Show file extensions, dangerous extensions and graphics formats. See also domain extension.
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