3.1 may refer to:
* An approximation of the mathematical constant
π
* A shorthand reference to release 3.1 of some piece of software, such as
Windows 3.1x
Windows 3.1 is a major release of Microsoft Windows. It was released to manufacturing on April 6, 1992, as a successor to Windows 3.0.
Like its predecessors, the Windows 3.1 series ran as a shell on top of MS-DOS. Codenamed Janus, Windows 3 ...
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