Media Structure - USB Mass Storage: Designing and Programming Devices and Embedded Hosts - page 172

Table 7-1: A partition table entry contains information that enables the master
computer to access locations in the storage media.
Byte in the
Partition-table Entry

Size
(bytes)

Description

0 1 Boot indicator

00h = do not boot from this partition
80h = boot from this partition

1 1 CHS addressing: starting head number

2 2 CHS addressing:

bits 5..0: starting sector number
bits 7..6: starting cylinder number, bits 9...8
bits 15..8: starting cylinder number, bits 7..0

4 1 Partition type

5 1 CHS addressing: ending head number

6 2 CHS addressing:

bits 5..0: ending sector number
bits 7..6: ending cylinder number, bits 9...8
bits 15..8: ending cylinder number, bits 7..0

8 4 LBA: the sector number of the partition's first sector,

expressed as an offset from the MBR sector (sector zero)

12 4 Total number of sectors in the partition

mation. There is no defined limit to the number of extended partitions a
device can contain.

The Boot Signature

The boot signature is the final item in the MBR sector. Byte 510 (1FEh)
must equal 55h and byte 511 (1FFh) must equal AAh.