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The File Extension Library

What is a file extension?

Short answer: it's the set of letters after the period (.) in the name of a file.

Long answer: File extensions signify the file format of a file. It tells the operating system (OS) how data was stored in the file. Not all OS, require a file extension though. For instance, this is optional in Unix, but is mandatory with MS-DOS and Windows systems.

In most file formats the file type is actually defined by the contents (first bytes, file structure), but extensions are used to define the application that is used for opening the file.

Below is a detailed database of thousands of file extensions our team has compiled for you. Feel free to browse!


Browse all Extensions:
ABCDEFGHIJKLMNOPQRSTUVWXYZ
ONE - Extension Details
Date Added: August 10, 2008
File Extension:  .ONE
Description 1: .ONE is the extension used for documents created with the OneNote application program. Microsoft is the firm behind this notetaking software. It is capable of accepting digitized handwriting along with typed input. The program often includes objects or text pasted from other programs or applications like audio/video clips, images and drawings.
File Type:   Data file
Mode: ASCII
Program(s) to Open:  Windows: Microsoft OneNote
Common:
Extension: