Source: http://ubuntuforums.org/showthread.php?t=1806831
Some explanation on the booting proces and what is mounting etc...
When you press the power button, than the BIOS loads. The BIOS is fixed on your mother board. As a last step, the BIOS looks at the first record of the first (or only) harddisk. That record is called the mbr (master boot record).
The computer starts executing what is on the mbr.