The .xls extension is given to spreadsheets that have been created in versions of Microsoft Excel that were published prior to the 2007 edition of the product. Microsoft Excel 2007 and later versions now use the .xlsx format rather than the .xls extension. This is due to the fact that the newer Excel software utilizes xml formatting for increased program and file efficiency.
Microsoft Excel is included in the Microsoft Office suite, although it can also be purchased individually. Excel is the application that is most commonly used to create spreadsheet documents, so most of the spreadsheets created today have the .xls or .xlsx file extension.
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