Format of hard disk master boot sector:
Offset	Size	Description	)
 00h 446 BYTEs	Master bootstrap loader code
1BEh 16 BYTEs	partition record for partition 1 (see #00651)
1CEh 16 BYTEs	partition record for partition 2
1DEh 16 BYTEs	partition record for partition 3
1EEh 16 BYTEs	partition record for partition 4
1FEh	WORD	signature, AA55h indicates valid boot block