The disk dump, dd command is awesome. It can be used for creating backups, copying files, even for writting CDs or DVDs.
In this article I will show you how to backup your MBR (Master Boot Record) with dd.
So, backup the Partition Table (or MBR), for /dev/sdb:
# dd if=/dev/sdb of=/root/sdambr.bak bs=512 count=1
If you damage the Partition Table, you can easily restore it, with the same dd command, on /dev/sdb:
# dd if=/root/sdambr.bak of=/dev/sdb bs=1 count=64 skip=446 seek=446
/dev/sda represents the first S-ATA or SCSI hard disk and /dev/sdb the second S-ATA or SCSI hard disk. Read more about hard disk representations here.