(1) DBR is located in Cylinder 0, Head 1, and Sector 1 and its logical sector number is0
(2) DBR contains DOS Boot Program and BPB.
(3) BPB is very important and the logical address and physical address can be calculated by BPB.
All of above are taking DOS (FAT16) for example, although it is not applied nowadays. However, the location of Track 0, Cylinder 1 and Sector 1 also has the analogous functions. More precisely, DBR should be renamed as OBR (OS Boot record). For example, OBR (FAT32 or NTFS) evolved from DBR of DOS. And OBR (DBR) is generated by advanced format programs such as FORMAT, PM, DM, DISKPART, WINXP, MiniTool Partition Wizard and so on.
DBR (DOS BOOT RECORE) is located in Cylinder 0, Head 1 and Sector 1(Logical Sector 0). And it is divided into two parts: DOS Bootstrapper and BPB (Parameter block of BIOS). Among them, DOS is responsible for the location and loading of DOS system files(IO.SYS, MSDOS.SYS) and BPB is applied to describe disk information in this DOS partition. BPB is located in 0BH offset of DBR, 13 bytes. It contains the parameters used in logical format, which can provide parameters for calculation of FAT, initial address of directory and data area in DOS and physical format (low level format) of the three characters after BPB. Through the information, Boot strapper or device driver transfer the logical address (DOS sector) into physical address (absolute sector) in disk.
BPB format, sequence number, offset address, sigificance
1 03H－0AH OEM Number
2 0BH－0CH Number of bytes in every sector
3 0DH Number of sectors in every cluster
4 0EH－0FH Number of reserved sectors
5 10H FAT Number of backups
6 11H－12H Number of Boot Directory terms
7 13H－14H Total number of sectors in disk
8 15H Description of medium
9 16H－17H Number of sectors in every FAT
10 18H－19H Number of sectors in every track
11 1AH－1BH Heads
12 1CH－1FH Number of special implicit sectors
13 20H－23H Total number of sectors
14 24H－25H Number of physical drives
16 27H－2AH Serial number of volumes
17 2BH－35H Volume labels
18 36H－3DH Number of file system
Formulas of DOS Boot Record
Formulas of DOS Boot Record:
FAT ≡ Sectors reserved
Boot directory ≡ Sectors reserved + number of FAT × number of sectors in every FAT
Data area ≡ number of logical sectors in Boot Directory + (32×number of directory terms in Boot Directory + (number of bytes in every sector-1)) DIV number of bytes in every sector
Number of absolute sectors≡ number of logical sectors + number of implicit sectors
Number of sectors ≡ (number of absolute sectors MOD number of sectors in every track) + 1
Heads ≡ (number of absolute sectors DIV number of sectors in every track) MOD number of head
Number of track ≡ (number of absolute sectors DIV number of sectors in every track) DIV heads