[ Thanks to Falko
Timme for this link. ]
“Xen lets you create guest operating systems (*nix operating
systems like Linux and FreeBSD), so called “virtual machines” or
domUs, under a host operating system (dom0). Using Xen you can
separate your applications into different virtual machines that are
totally independent from each other (e.g. a virtual machine for a
mail server, a virtual machine for a high-traffic web site, another
virtual machine that serves your customers’ web sites, a virtual
machine for DNS, etc.), but still use the same hardware. This saves
money, and what is even more important, it’s more secure. If the
virtual machine of your DNS server gets hacked, it has no effect on
your other virtual machines. Plus, you can move virtual machines
from one Xen server to the next one.”