I hope I have this right.....
A hard drive has the boot sector as the first sector--it is not associated with any particular partition. The last entries in the boot sector are the partition table for 4 primary or extended partitions. If there are more partitions, they appear in the SECOND sector of the drive.
In my system, the real data starts in sector 63---ie 0-62 are used for the boot sector, partition tables and ??.
Google for a reference on partition table format, boot record format, etc. Then use dd to explore your drives
For example: dd if=/dev/hda of=filename bs=512 count=1 will put the first 512byte sector into a file named "filename". Then run this thru hexdump to see the data. (in place of hda, put your drive number---which you can find by looking at mtab, fstab, or by using fdisk.)