XLS

XLS is the filename extension for a proprietary binary spreadsheet file format used by Microsoft Excel prior to the 2007 release. The format stores workbook data in the Binary Interchange File Format (BIFF) and was used by Excel versions from Excel 97 through Excel 2003.

In 2007, Microsoft introduced the Office Open XML-based .xlsx format, which uses ZIP compression and an internal XML schema. The .xls format remains supported for backward compatibility, but new features are generally not added to it, and modern Excel emphasizes .xlsx/.xlsm/.xlsb.

A typical XLS file contains one or more worksheets with cells that hold numbers, text, dates, and formulas; formatting, charts, and embedded objects may be included. Macros could be stored in older workbooks; macro-enabled variants use .xlsm.

Limitations include a maximum of 65,536 rows and 256 columns per worksheet, and certain newer data types or features are not available. Data can be lost or reformatted when converting to newer formats.

Compatibility: read/write supported by major spreadsheet programs (Microsoft Excel, LibreOffice, Google Sheets) but formatting or advanced features may not be preserved exactly.

Today the .xls format is primarily encountered for legacy data and interoperability with older software, with gradual replacement by .xlsx in new documents.