Partition table

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A partition table is a logical division of a hard disk. Partitioning of a hard disk allows the following:

A hard drive's partition table is located within the MBR (master boot record), or the first sector of the hard drive, and contain 64 bytes of partition table information. There are four 16 byte partition table entries.

Master Boot Record
(offset)
0x0000 to 0x01BD - First 446 bytes
0x01BE to 0x01CD - Partition entry 1
0x01CE to 0x01DD - Partition entry 2
0x01DE to 0x01ED - Partition entry 3
0x01EE to 0x01FD - Partition entry 4
0x01FE to 0x01FF - Boot signature

Your operating system will look for the 2 byte boot signature at the end of the partition table to determine the boot sector.

Each partition table consists of the following:

Boot indicator (0x00 for off, 0x80 for on)   -- 1 Byte
Starting head, cylinder and sector           -- 3 Bytes
Filesystem descriptor                        -- 1 Byte
Ending head, cylinder and sector             -- 3 Bytes
Starting sector (relative to disk beginning) -- 4 Bytes
Number of sectors in partition               -- 4 Bytes

All bytes are arranged in little endian

Following is a sample partition table layout:

offset: value                  explanation
======: =====                  ===========
0x01BE: 0x80                   bootable flag (0x00 for flag off, 0x80 for on)
0x01BF: 0x00 0x02 0x00         starting head, cylinder and sector
0x01C2: 0x83                   filesystem descriptor
0x01C3: 0x1A 0x5B 0x8C         ending head, cylinder and sector
0x01C6: 0x02 0x00 0x00 0x00    starting sector (relative to beginning of disk)
0x01CA: 0x00 0x35 0x0C 0x00    number of sectors in partition