Compound File Binary Format (CFBF), also called Compound File, Compound Document format, or Composite Document File V2 (CDF), is a

compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive struct ...

document file format A document file format is a text or binary file format for storing documents on a storage media, especially for use by computers. There currently exist a multitude of incompatible document file formats. Examples of XML-based open standards ar ...

for storing numerous files and streams within a single file on a disk. CFBF is developed by

Microsoft Microsoft Corporation is an American multinational corporation, multinational technology company, technology corporation producing Software, computer software, consumer electronics, personal computers, and related services headquartered at th ...

and is an implementation of Microsoft

COM Structured Storage COM Structured Storage (variously also known as ''COM structured storage'' or '' OLE structured storage'') is a technology developed by Microsoft as part of its Windows operating system for storing hierarchical data within a single file. Stri ...

. Microsoft has opened the format for use by others and it is now used in a variety of programs from

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and

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to Business Objects. It also forms the basis of the

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.AMW Association (formerly AAF Association)

Overview

At its simplest, the Compound File Binary Format is a container, with little restriction on what can be stored within it. A CFBF file structure loosely resembles a

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. The file is partitioned into ''Sectors'' which are chained together with a ''File Allocation Table'' (not to be mistaken with the file system of the same name) which contains chains of sectors related to each file, a ''Directory'' holds information for contained files with a Sector ID (SID) for the starting sector of a chain and so on.

Structure

The CFBF file consists of a 512-Byte header record followed by a number of sectors whose size is defined in the header. The literature defines Sectors to be either 512 or 4096 bytes in length, although the format is potentially capable of supporting sectors ranging in size from 128-Bytes upwards in powers of 2 (128, 256, 512, 1024, etc.). The lower limit of 128 is the minimum required to fit a single directory entry in a Directory Sector. There are several types of sector that may be present in a CFBF: * File Allocation Table (FAT) Sector – contains chains of sector indices much as a FAT does in the FAT/FAT32 filesystems * MiniFAT Sectors – similar to the FAT but storing chains of mini-sectors within the Mini-Stream * Double-Indirect FAT (DIFAT) Sector – contains chains of FAT sector indices * Directory Sector – contains directory entries * Stream Sector – contains arbitrary file data * Range Lock Sector – contains the byte-range locking area of a large file More detail is given below for the header and each sector type.

CFBF Header format

The CFBF Header occupies the first 512 bytes of the file and information required to interpret the rest of the file. The C-Style structure declaration below (extracted from the AAFA's Low-Level Container Specification) shows the members of the CFBF header and their purpose: typedef unsigned long ULONG; // 4 Bytes typedef unsigned short USHORT; // 2 Bytes typedef short OFFSET; // 2 Bytes typedef ULONG SECT; // 4 Bytes typedef ULONG FSINDEX; // 4 Bytes typedef USHORT FSOFFSET; // 2 Bytes typedef USHORT WCHAR; // 2 Bytes typedef ULONG DFSIGNATURE; // 4 Bytes typedef unsigned char BYTE; // 1 Byte typedef unsigned short WORD; // 2 Bytes typedef unsigned long DWORD; // 4 Bytes typedef ULONG SID; // 4 Bytes typedef GUID CLSID; // 16 Bytes struct StructuredStorageHeader ;

File Allocation Table (FAT) Sectors

When taken together as a single stream the collection of FAT sectors define the status and linkage of every sector in the file. Each entry in the FAT is 4 bytes in length and contains the sector number of the next sector in a FAT chain or one of the following special values: * FREESECT (0xFFFFFFFF) – denotes an unused sector * ENDOFCHAIN (0xFFFFFFFE) – marks the last sector in a FAT chain * FATSECT (0xFFFFFFFD) – marks a sector used to store part of the FAT * DIFSECT (0xFFFFFFFC) – marks a sector used to store part of the DIFAT

Range Lock Sector

The Range Lock Sector must exist in files greater than 2GB in size, and must not exist in files smaller than 2GB. The Range Lock Sector must contain the byte range 0x7FFFFF00 to 0x7FFFFFFF in the file. This area is reserved by Microsoft's COM implementation for storing byte-range locking information for concurrent access.

Glossary

* ''FAT'' – File Allocation Table, also known as: ''SAT'' – Sector Allocation Table * ''DIFAT'' – Double-Indirect File Allocation Table * ''FAT Chain'' – a group of FAT entries which indicate the sectors allocated to a Stream in the file * ''Stream'' – a virtual file which occupies a number of sectors within the CFBF * ''Sector'' – the unit of allocation within the CFBF, usually 512 or 4096 Bytes in length

References

External links

* * * * {{cite web , accessdate = 6 July 2019 , url = https://www.loc.gov/preservation/digital/formats/fdd/fdd000380.shtml , title = Microsoft Compound File Binary File Format, Version 3 , publisher = Library of Congress, Digital Formats web site Computer file formats Digital container formats