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XLS – Microsoft Excel Binary File Format

Format introduction

Microsoft Excel up until 2007 version used a proprietary binary file format called Excel Binary File Format (.XLS) as its primary format. Excel 2007 uses Office Open XML as its primary file format, an XML-based format that followed after a previous XML-based format called “XML Spreadsheet”.

Technical details

OpenOffice.org has created documentation of the Excel format. Since then Microsoft made the Excel binary format specification available to freely download.