MICROSOFT EXCEL FILE FORMAT

MICROSOFT EXCEL FILE FORMAT

Microsoft Excel is a popular spreadsheet.  It uses a file format called BIFF (Binary

File Format).  There are many types of BIFF records.  Each has a 4 byte header.  The

first two bytes are an opcode that specifies the record type.  The second two bytes

specify record length.  Header values are stored in byte-reversed form (less significant

byte first).  The rest of the record is the data itself (Figure 2-1).

 

Figure 2-1.  BIFF record header.

                 |  Record Header    |  Record Body

Byte Number       |  0    1    2    3 |  0    1   ...

                -----------------------------------

Record Contents    | XX | XX | XX | XX | XX | XX | ...

                -----------------------------------

                | opcode   | length  | data

                            

Each X represents a hexadecimal digit

Two X's form a byte.  The least significant (low) byte of the opcode is byte 0 and the

most significant (high) byte is byte 1.  Similarly, the low byte of the record length

field is byte 2 and the high byte is byte 3.

 

BOF (Beginning of File)

The first record in every spreadsheet is always of the BOF type (Figure 2-2).  

Figure 2-2.  BOF record.

           |  Record Header  |   Record Body   |

Byte       |  0   1   2    3 |  0   1   2   3 |

           -----------------------------------------

Contents   | 09 | 00 | 04 | 00 | 02 | 00 | 10 | 00 |

           -----------------------------------------

           | opcode  | length  | version |  file   |

           |        |        | number |  type  |