BIFF4

BIFF4 stands for Binary Interchange File Format version 4, a historical binary format used by early Microsoft Excel spreadsheets to store workbook data. It belongs to the BIFF family of formats that accompanied Excel in its early years and was eventually superseded by later versions such as BIFF5 and BIFF8. BIFF4 files are largely obsolete today but remain relevant for archival, data recovery, and historical study of spreadsheet software.

The format is binary and record-based. A BIFF4 file comprises a sequence of records, each with a two‑byte type identifier and a two‑byte length field, followed by data in little-endian encoding. Common record types include those that mark the beginning and end of the file (for example, BOF and EOF), define the workbook and worksheet structure (such as DIMENSIONS), and store cell content. Cells can hold numeric values, strings, or formula results, and the file can also include records related to formatting, dimensions, and basic metadata. The design emphasizes compact storage and relatively fast parsing on the hardware available at the time of its use.

Historically, BIFF4 was used by early versions of Excel on Windows and Macintosh platforms in the 1990s. It was part of a progression from earlier BIFF versions toward more feature-rich formats, culminating in later BIFF5, BIFF8, and the modern descendants used in newer Excel releases. Today, BIFF4 is largely of interest to historians, developers working with legacy data, and those performing data recovery from old Excel workbooks. Modern spreadsheet interoperability relies on newer formats, while BIFF4 remains documented mainly through reverse-engineering efforts and historical references.