678 Microsoft Excel 2.x Worksheet (xls) 2 Microsoft Excel Worksheet (2.1) Spreadsheet None The Binary Interchange File Format (BIFF) is a spreadsheet file format developed by Microsoft. BIFF 2 is the native file format of Microsoft Excel 2.1 for Windows. The format is proprietary and Microsoft does not make details of its structure public. The information contained here is derived primarily from OpenOffice.org's reverse-engineered documentation of the format, and should not therefore be regarded as definitive. BIFF is a stream based format, and a BIFF 2 file comprises a single worksheet stream, containing a Beginning of File (BOF) record, followed by a series of Worksheet records, and terminated by an End of File (EOF) record. Binary Little-endian (Intel) 1 Digital Preservation Department / The National Archives 11 Mar 2005 19 Jul 2013 application/vnd.ms-excel MIME com.microsoft.excel.xls Apple Uniform Type Identifier fmt/55 PUID xls File extension 72 BIFF 2 Worksheet BIFF2: BOF hex 0900. record length hex 0400, BIFF version (not used), filetype=worksheet=1000 1 Absolute from BOF 0 09000400{2}1000 Is previous version of 679 Microsoft Excel 3.0 Worksheet (xls) Is supertype of 1341 Microsoft Excel Chart Is supertype of 1343 Microsoft Excel Macro