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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
U3I - Extension Details
Date Added: January 01, 1970
File Extension:  .U3I
Description 1: .U3I files contain info concerning a U3 program application (.U3P file) in XML format. Aside from the version of the application, this file format also includes the working parameters and download path. "Manifest.u3i is how U3I files are commonly named. The U3 Launcher uses these files in describing different U3 applications.
File Type:   Text file
Mode: ASCII
Program(s) to Open:  Windows: referenced by U3 Launcher, editable with a text editor
Common:
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