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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:
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XLSX - Extension Details
Date Added: January 01, 1970
File Extension:  .XLSX
Description 1: The .XLSX extension is linked to the spreadsheet format that Microsoft Excel 2007 (a part of Office 12) introduced. This format is used when storing data in cells that are organized in columns and rows. Files of this type are based on the format Open XML and feature ZIP compression to allow for smaller filesizes. .XLSX files offer backward compatibility with Microsoft Office 2003, 2000 and Office XP through component support.
File Type:   Data file
Mode: ASCII
Program(s) to Open:  Windows: Excel 2000, 2003, XP with Compatibility Pack installed, OpenOffice.org Calc, Windows Server with GemBox Spreadsheet .NET component, Microsoft Excel 2007, OxygenOffice Professional, Panergy docXConverter Macintosh: Apple Numbers (part of iWork 08), OpenOffice.org Calc, Microsoft Excel 2008, Panergy docXConverter Unix: OxygenOffice Professional
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