In this chapter, we discussed the major architectural components of the Xen system. The Xen hypervisor sits between the guest domains and the physical hardware, allocating and controlling resources, enforcing protection and isolation. Domain0 is a special privileged domain used to administer normal guest domains and to control the physical hardware. The Xen management daemon, xend, passes control requests to the Xen hypervisor. XenStore is a database of configuration information used to communicate between domains.