Microsoft Excel 4.0 Workbook (xls) 4W
Unknownspreadsheet · also known as Microsoft Excel Workbook (4.0)
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.
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| Extensions | .xlw |
|---|---|
| MIME types | application/vnd.ms-excel |
| Signatures | 09040600 at byte 0 (BIFF 4 Workbook/Workspace) |
| PRONOM | fmt/58 |
| Wikidata | Q63036234 |
| Apple UTI | com.microsoft.excel.xls |
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From PRONOM, Wikidata. Updated 2026-10-20.