681 Microsoft Excel 4.0 Workbook (xls) 4W Microsoft Excel Workbook (4.0) Spreadsheet None The Binary Interchange File Format (BIFF) is a spreadsheet file format developed by Microsoft. BIFF 4W is a native file format of Microsoft Excel 4.0 for Windows. Excel 4.0 allowed either a single worksheet to be stored as a worksheet file (BIFF 4S), or for multiple worksheets to be combined in a single workbook file (BIFF 4W). 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 4W file comprises a Workbook Globals Substream, containing a Beginning of File (BOF) record, one or more embedded Worksheet streams (in BIFF 4S format), 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/58 PUID xlw File extension 75 BIFF 4 Workbook/Workspace BIFF4: BOF hex 0904. record length hex 0600, BIFF version=(0000|0004), filetype=workbook=0001 1 Absolute from BOF 0 09040600(0000|0004)0001 Is previous version of 682 Microsoft Excel 5.0/95 Workbook (xls) Is subsequent version of 679 Microsoft Excel 3.0 Worksheet (xls)