What Is the Disk Parameter Block?

Disk Parameter Block Definition (DPB)

The disk parameter block, also known as DPB or media parameter block, is one component of the volume boot record and contains details about a disk's volume.

Some of the volume details stored in the disk parameter block include the volume label, the volume serial number, volume size, and other information about the structure of the volume.

Disk Parameter Block Structure and Location

Offset Length (Bytes) Description
00h 1 Drive number; 0=A, 1=B
01h 1 Driver unit number
02h 2 Bytes per sector
04h 1 Sectors per cluster, minus 1
05h 1 Shift count to convert clusters into sectors
06h 2 Reserved sectors at beginning of drive
08h 1 Number of FAT copies
09h 2 Number of root directory entries
0Bh 2 Number of first sectors containing user data
0Dh 2 Number of clusters plus 1
0Fh 2 Number of clusters used by first FAT
11h 2 First sector of root directory
13h 2 Driver header address
17h 1 Media ID
18h 1 00h if disk is accessed; FF if not
19h 4 Pointer to next DPB
1Dh 2 Starting cluster for free space search
1Fh 2 Number of free clusters; FFFFh if unknown