Microsoft Excel files have an.xls extension. A file format, the Open Office XML file format, was introduced in 2007 to replace the XLS extension in Excel. Several DOS-based application file formats are supported by Excel 2007, which is backward compatible. Third-party apps (such as browsers) frequently make use of Excel as a workaround for implementing binary file formats. There are XLS files that carry information about spreadsheet spreadsheets and include the worksheet information, macros, tables, calculations, and charts. The Visual Basic software terminology also made use of this file extension. As part of Microsoft Office, Excel runs on both Mac OS and Windows. Spreadsheet XML is utilized for its simplicity, but it lacks several advanced features. A file format that's proprietary binary was utilized by Excel until 2007 to format its data. Individual workbooks and their templates can be customized in this way. DIF, SYLK, DBF, and CSV, are examples of legacy formats that Excel is capable of preparing. File extensions have replaced it, including XLSX, XLS, XLSB, and XLS. Excel 2007 stayed backward compatible when XLS files were replaced. It means that the XLS file remains highly efficient. You can open XLS files with: OpenOffice, Microsoft Excel Viewer, Microsoft Excel.