computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, e ...

, the BIOS parameter block, often shortened to BPB, is a

data structure In computer science, a data structure is a data organization, management, and storage format that is usually chosen for efficient access to data. More precisely, a data structure is a collection of data values, the relationships among them, a ...

in the volume boot record (VBR) describing the physical layout of a

data storage Data storage is the recording (storing) of information (data) in a storage medium. Handwriting, phonographic recording, magnetic tape, and optical discs are all examples of storage media. Biological molecules such as RNA and DNA are conside ...

volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). The de ...

. On partitioned devices, such as

hard disks A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magneti ...

, the BPB describes the volume partition, whereas, on unpartitioned devices, such as

floppy disk A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...

s, it describes the entire medium. A basic BPB can appear and be used on any partition, including floppy disks where its presence is often necessary; however, certain filesystems also make use of it in describing basic filesystem structures. Filesystems making use of a BIOS parameter block include

FAT12 File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...

(except for in DOS 1.x),

FAT16 File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on Hard disk drive, hard disks and other devices. It is often supported for compatibi ...

FAT32 File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by c ...

, HPFS, and

NTFS New Technology File System (NTFS) is a proprietary journaling file system developed by Microsoft. Starting with Windows NT 3.1, it is the default file system of the Windows NT family. It superseded File Allocation Table (FAT) as the preferred fil ...

. Due to different types of fields and the amount of data they contain, the length of the BPB is different for FAT16, FAT32, and NTFS boot sectors. (A detailed discussion of the various FAT BPB versions and their entries can be found in the

FAT In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers spec ...

article.) Combined with the 11-byte data structure at the very start of volume boot records immediately preceding the BPB or EBPB, this is also called FDC descriptor or extended FDC descriptor in ECMA-107 or ISO/IEC 9293 (which describes FAT as for flexible/floppy and optical disk cartridges).

FAT12 / FAT16

DOS 2.0 BPB

Format of standard DOS 2.0 BPB for

(13 bytes):

DOS 3.0 BPB

Format of standard DOS 3.0 BPB for

and

(19 bytes), already supported by some versions of MS-DOS 2.11:

DOS 3.2 BPB

Format of standard DOS 3.2 BPB for

and

(21 bytes):

DOS 3.31 BPB

Format of standard DOS 3.31 BPB for

and

FAT16B File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...

(25 bytes):

DOS 3.4 EBPB

Format of PC DOS 3.4 and OS/2 1.0-1.1 Extended BPB for

and

(32 bytes):

FAT12 / FAT16 / HPFS

DOS 4.0 EBPB

Format of DOS 4.0 and OS/2 1.2 Extended BPB for

and HPFS (51 bytes):

FAT32

DOS 7.1 EBPB

Format of short DOS 7.1 Extended BIOS Parameter Block (60 bytes) for

: Format of full DOS 7.1 Extended BIOS Parameter Block (79 bytes) for

NTFS

Format of Extended BPB for

(73 bytes):

exFAT BPB

exFAT does not use a BPB in the classic sense. Nevertheless, the volume boot record in sector 0 is organized similarly to BPBs.

References

* — a description of BPBs, from version 2.0 to version 7.0 * — In the "processing the BIOS parameter block" section the authors describe the evolution of the BIOS parameter block from the MS-DOS version 2.0 BPB to the PC DOS version 4.0 BPB, and label each field with the DOS version that introduced it. * — Figure 4.3 contains a diagram of the version 4.0 BPB and states that the layout of BPBs "is not defined by Microsoft and can vary with different vendors". At the time that the book was written, this was true. Microsoft first publicly documented the BPB structure in the OS/2 Developers' Toolkit. * — Verstak reverse engineers the BIOS parameter block. The paper contains several errors. One such is its statement that "the presence of the EBPB in FAT32 is not documented by Microsoft". See: ** — Microsoft documents a version 4.0 BPB and a new "FAT32 BIOS Parameter Block (BPB)" (a version 7.0 BPB) for DOS-Windows 98 that is "larger than a standard BPB", has an "identical structure to a standard BPB", but that also "includes several extra fields". ** — Microsoft documents extended BPBs on both FAT16 and FAT32 volumes. It also documents BPBs on NTFS volumes. * — The table "BPB and Extended BPB Fields on NTFS Volumes" describes BPBs on NTFS volumes. The descriptions of several fields contradict those given in the Windows 2000 Resource Kit. * — an issue that affects BPBs *

* — on the misuse of OEM labels and Microsoft's Volume Tracker * * * * * * {{cite newsgroup , title=Evil :) DOS6 FAT , author-first=Jen , author-last=Kilmer , date=2013-05-21 , newsgroup=comp.os.os2.misc , url=https://groups.google.com/forum/?hl=la#!msg/comp.os.os2.misc/dxxRtZ_V-fU/YVvnukmtfvAJ , access-date=2019-07-29 , url-status=live , archive-url=https://web.archive.org/web/20220529153802/https://groups.google.com/g/comp.os.os2.misc/c/dxxRtZ_V-fU/m/YVvnukmtfvAJ , archive-date=2022-05-29 BIOS DOS technology