Partition Table
The information about primary partitions and an extended partition is contained in the Partition Table, a 64-byte data structure located in the first sector (cylinder 0, head 0, sector 1) of the hard drive. The Partition Table conforms to a standard layout that is independent of the operating system. Each Partition Table entry is 16 bytes long, making a maximum of four entries available. Each entry starts at a predetermined offset from the beginning of the sector, as follows:
| Partition number | Offset |
|---|---|
| Partition 1 | 0x01BE (446) |
| Partition 2 | 0x01CE (462) |
| Partition 3 | 0x01DE (478) |
| Partition 4 | 0x01EE (494) |
Each entry has the following structure:
| Element | Size | Description |
|---|---|---|
| 0 | byte | Boot indicator, 00 = no, 80 = bootable |
| 1 | byte | Starting head |
| 2 | 6 bits | Starting sector (Bits 6-7 are the upper two bits for the Starting Cylinder field.) |
| 3 | 10 bits | Starting Cylinder |
| 4 | byte | System ID |
| 5 | byte | Ending Head |
| 6 | 6 bits | Ending Sector (Bits 6-7 are the upper two bits for the ending cylinder field) |
| 7 | 10 bits | Ending Cylinder |
| 8 | dword | Relative Sector (to start of partition) |
| 12 | dword | Total Sectors in partition |