CSV to XLS Converter

XLS is the binary spreadsheet format of Microsoft Excel, first introduced with Excel 1.0 for Macintosh in September 1985 and becoming the dominant spreadsheet format worldwide. The format stores workbooks as OLE2 compound document files using the Binary Interchange File Format (BIFF), organizing sheets, cells, formulas, formatting, charts, pivot tables, macros, and metadata across multiple internal streams. Each cell record encodes the cell's value (number, string, boolean, error, or formula), position, and formatting index, while shared string tables and style records reduce redundancy. The format evolved through BIFF versions (BIFF2 through BIFF8), with BIFF8 (Excel 97) establishing the structure used through Excel 2003. XLS supports up to 65,536 rows and 256 columns per sheet, a limit that drove the creation of XLSX. One advantage is universal spreadsheet compatibility — XLS files are recognized by every major spreadsheet application including LibreOffice Calc, Google Sheets, Apple Numbers, and dozens of programming libraries across all platforms. The format's mature feature set is another strength: XLS handles complex formulas, conditional formatting, data validation, named ranges, array formulas, external references, and VBA macros. Although XLSX replaced XLS as the default in Office 2007, the binary format persists in financial institutions, legacy reporting systems, and any environment where Excel 97-2003 compatibility is required.