[ 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.”