The traditional representation of a Xen-based system shows several virtual machines (known in Xen as domains) sitting on top of the hypervisor, which itself sits directly on the hardware (Figure 7-4). When it boots up, the hypervisor launches a special domain, known as domain zero. Domain zero has special privileges that allow it to manage the rest of the system, and it is analogous to a root or administrator process in a regular operating system. Figure 7-4 shows a typical Xen-based system, with domain zero and several guest domains (known as DomUs in Xen jargon) running on top of the Xen hypervisor.
Figure 7-4. Xen system architecture