The best way to understand “how it works” is to look at a practical case, which is what we're going to do here. Suppose you have just purchased a brand new hard disk with no partitions on it. Your Mandrakelinux partition is completely full, and rather than starting again from scratch, you decide to move a whole section of the tree structure to your new hard disk. Because your new disk has a large capacity, you decide to move your biggest directory to it: /usr. But first, a bit of theory.