XLS: Excel Spreadsheet

What is XLS?

XLS is Microsoft Excel's legacy binary file format used from Excel 97 through 2003. As a proprietary binary format, XLS was the dominant spreadsheet format for over a decade before being replaced by the XML-based XLSX format.

While largely superseded, XLS files are still widely used and supported for compatibility with older systems and software.

Key Features

• Binary Format: Compact but proprietary structure
• Worksheet Limit: 65,536 rows × 256 columns
• Multiple Sheets: Multiple worksheets per file
• Formulas: Excel calculation engine support
• Charts & Graphics: Embedded visualizations
• Macros: VBA macro support
• Formatting: Cell styles and conditional formatting
• Wide Support: Legacy compatibility

Common Uses

• Legacy system compatibility
• Older Excel versions (pre-2007)
• Embedded systems with XLS support
• Simple data exchange
• Financial record archives
• Historical data preservation

Advantages

• Universal compatibility with older software
• Smaller files for simple spreadsheets
• Fast opening on older systems
• Well-established format
• Widely supported

Limitations

• Limited to 65,536 rows
• Larger files than XLSX
• Proprietary binary format
• No built-in error recovery
• More vulnerable to corruption
• Deprecated by Microsoft

Technical Information

XLS uses Microsoft's Binary Interchange File Format (BIFF), a proprietary binary format. Each version of Excel introduced new BIFF versions with enhanced features, with BIFF8 (Excel 97-2003) being the most widely supported.