BIOS Parameter Block

In computing, the BIOS parameter block, often shortened to BPB, is a data structure in the Volume Boot Record describing the physical layout of a data storage volume. On partitioned devices, such as hard disks, the BPB describes the volume partition, whereas, on unpartitioned devices, such as floppy disks, 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 (except for in DOS 1.x), FAT16, FAT32, HPFS, and NTFS. 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 article.) ECMA-107 or ISO/IEC 9293 (which describes FAT as for flexible/floppy and optical disk cartridges) also describes this as an FDC Descriptor or an FDC Extended Descriptor.

The standard BPB for FAT16 is as follows:

Field Field Length Hex offset Description
BytesPerSector WORD 0x000B Bytes Per Sector
SectorsPerCluster BYTE 0x000D Sectors Per Cluster
ReservedSectors WORD 0x000E Reserved Sectors
FatCopies BYTE 0x0010 Number of FATs
RootDirEntries WORD 0x0011 Root Entries
NumSectors WORD 0x0013 Small Sectors
MediaType BYTE 0x0015 Media Descriptor
SectorsPerFAT WORD 0x0016 Sectors Per FAT
SectorsPerTrack WORD 0x0018 Sectors Per Track
NumberOfHeads WORD 0x001A Number of Heads
HiddenSectors DWORD 0x001C Hidden Sectors
SectorsBig DWORD 0x0020 Large Sectors

Extended BPB for FAT16 Volumes:

Field Length Hex offset Description
BYTE 0x0024 Physical Drive Number
BYTE 0x0025 Reserved
BYTE 0x0026 Extended Boot Signature
DWORD 0x0027 Volume Serial Number
11 bytes 0x002B Volume Label
QWORD 0x0036 File System Type

Other articles related to "bios parameter block, block, parameters":

FATX - Technical Design - Boot Sector - BIOS Parameter Block
... structure of the first 25 bytes of the BIOS Parameter Block (BPB) used by FAT versions since DOS 2.0 (bytes at sector offset 0x00B to 0x017 are stored since DOS 2.0, but not always used before DOS 3.2 ... support only two FATs in their built-in disk driver, but support other FAT counts for block device drivers loaded later on ... before DOS 3.2 (86-DOS, MS-DOS/PC DOS 1.x and MSX-DOS version 1.0) ignore the boot sector parameters altogether and use the media descriptor value from the ...

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