XLS Microsoft Excel Spreadsheet (Legacy)

The original Excel file format was introduced in 1987 with the release of Microsoft Excel 1.0 for Macintosh computers.

At that time, the native file format used by Excel was called “Binary Interchange File Format” (BIFF). BIFF was a proprietary binary format developed by Microsoft specifically for storing spreadsheet data.

The first version of BIFF, known as BIFF1, was used in Excel 1.0 and supported basic spreadsheet functionality, such as cells, formulas, and formatting.

Over the years, Microsoft updated the BIFF format several times to add new features and improve performance. Some notable versions of BIFF include:

  • BIFF2 (Excel 3.0): Introduced support for charts, macros, and improved formatting.
  • BIFF3 (Excel 4.0): Added support for multiple worksheets, outlining, and enhanced formatting.
  • BIFF4 (Excel 5.0): Introduced support for pivot tables, conditional formatting, and other advanced features.
  • BIFF5 (Excel 95-97): Improved performance and added support for Unicode characters.

The BIFF format was widely used until the release of Excel 2007, which introduced a new file format called Office Open XML (OOXML) or more specifically, .xlsx (Excel Binary File Format). The OOXML format is based on XML and ZIP compression, making it more flexible and efficient than the older BIFF format.

Although Microsoft no longer uses BIFF as the default file format for Excel, many older versions of Excel still support reading and writing BIFF files.