The third major component of the boot sector is the BIOS Parameter Block (BPB). The disk parameter block is very important data area for DOS. It helps the DOS to find:
FAT32 DOS Boot Record Format |
Offset |
Description |
Size |
00H |
Jump Code + NOP |
3 Bytes |
03H |
OEM Name and Version |
8 Bytes |
0BH |
Bytes Per Sector |
2 Bytes |
0DH |
Sectors Per Cluster |
1 Byte |
0EH |
Reserved Sectors |
2 Bytes |
10H |
Number of Copies of FAT |
1 Byte |
11H |
Maximum Root Directory Entries (but Not Available for FAT32) |
2 Bytes |
13H |
Number of Sectors in Partition Smaller than 32MB (Therefore Not Available for FAT32) |
2 Bytes |
15H |
Media Descriptor (F8H for Hard Disks) |
1 Byte |
16H |
Sectors Per FAT (In Older FAT Systems and Not Available for FAT32) |
2 Bytes |
18H |
Sectors Per Track |
2 Bytes |
1AH |
Number of Heads |
2 Bytes |
1CH |
Number of Hidden Sectors in Partition |
4 Bytes |
20H |
Number of Sectors in Partition |
4 Bytes |
24H |
Number of Sectors Per FAT |
4 Bytes |
28H |
Flags (Bits 0-4 Indicate Active FAT Copy) (Bit 7 Indicates whether FAT Mirroring is Enabled or Disabled <Clear is Enabled>) (If FAT Mirroring is Disabled, the FAT Information is only written to the copy indicated by bits 0-4) |
2 Bytes |
2AH |
Version of FAT32 Drive (High Byte = Major Version, Low Byte = Minor Version) |
2 Bytes |
2CH |
Cluster Number of the Start of the Root Directory |
4 Bytes |
30H |
Sector Number of the File System Information Sector (Referenced from the Start of the Partition) |
2 Bytes |
32H |
Sector Number of the Backup Boot Sector (Referenced from the Start of the Partition) |
2 Bytes |
34H |
Reserved |
12 Bytes |
40H |
Logical Drive Number of Partition |
1 Byte |
41H |
Unused (Could be High Byte of Previous Entry) |
1 Byte |
42H |
Extended Signature (29H) |
1 Byte |
43H |
Serial Number or 32 – Bit Binary ID of Partition
(Binary ID of 32 Bits provided by the OS itself) |
4 Bytes |
47H |
Volume Name of Partition |
11 Bytes |
52H |
FAT Name (FAT32 in this case) |
8 Bytes |
5AH |
Executable Code |
420 Bytes |
1FEH |
Executable Marker or Magic Number (AAH 55H) |
2 Bytes |
