The Master Boot Record is the same for most of pretty much all Operating System. As long as the platform is following x86 PC architecture (IBM PC). It is located on the first sector of Hard Drive at Cylinder 0, Head 0, Sector 1 (That mean, it start at physical address 0x00). It is the first piece of code that your computer runs after it has checked all of your hardware (POST) and turned control of loading software over the hard driver. This sector contain hard disk boot loader (ROM BIOS bootstrap routine), where the code can understand by PC BIOS. It aslo contains the partition table, which defines the difference sections of your hard drive. Basically if anything happens to this little 512 byte section, your hard driver is brain dead. This section will change partition table when your doing OS level formatting. Except your doing Fdisk (knows as Low level format) will change the Master Boot Record.
Partition Table
Partition table is a small part of master boot record. It contain the partition start and end physical address.
Master Boot Record and Partition Boot Record in physical address
| Address | Length | Description |
|---|---|---|
| 0x0000 to 0x01BD | 446 bytes | Boot Loader Code |
| 0x01BE to 0x01CD | 16 bytes | Partition entry 1 |
| 0x01CE to 0x01DD | 16 bytes | Partition entry 2 |
| 0x01DE to 0x01ED | 16 bytes | Partition entry 3 |
| 0x01EE to 0x01FD | 16 bytes | Partition entry 4 |
| 0x01FE to 0x01FF | 16 bytes | Boot Record signature (55 AA) |
Details of Partition Entry Table
| Length | Description |
|---|---|
| 1 | Boot indicator (0x00 = Inactive, 0x80 = Active) |
| 3 | Starting head, cylinder and sector (refer Head, Cylinder and sector) |
| 1 | File system descriptor (refer Partition Type Listing) |
| 3 | Ending head, cylinder and sector |
| 4 | Starting sector (offset to disk start) |
| 4 | Number of sector in partition |
Head, Cylinder and sector
| Cylinder Bit 7 to 0 (MSB) | Cylinder Bits 9+8 | Sector Bits 5 to 0 | Head Bit (LSB) |
Partition Type Listing
Table at below only show the Microsoft partition type listing
| Value | Description |
|---|---|
| 0x00 | Unknown or Nothing |
| 0x01 | 12-bit FAT |
| 0x04 | 16-bit FAT (Partition Smaller than 32MB) |
| 0x05 | Extended MS-DOS Partition |
| 0x06 | 16-bit FAT (Partition Larger than 32MB) |
| 0x0B | 32-bit FAT (Partition Up to 2048GB) |
| 0x0C | Same as 0x0B, but uses LBA 0x13 Extensions |
| 0x0E | Same as 0x06, but uses LBA 0x13 Extensions |
| 0z0F | Same as 0x05, but uses LBA 0x13 Extensions |
[Note] LBA - Logical Block Addressing - Uses the Interrupt 0x13 extension built into newer BIOS to access data above the 8GB barrier, or to access strictly in LBA mode, instead of CHS (Cylinder, Head Sector)
Reference
FAT32 Disk structure
FDISK / MBR rewrites the Master Boot Record
Master Boot Record (x86)
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