Architecture
Xen is a native, or bare-metal hypervisor. It runs in a more privileged CPU state than any other software on the machine.
Responsibilities of the hypervisor include memory management and CPU scheduling of all virtual machines ("domains"), and for launching the most privileged domain ("dom0") - the only virtual machine which by default has direct access to hardware. From the dom0 the hypervisor can be managed and unprivileged domains ("domU") can be launched.
The dom0 domain is typically a modified version of Linux, NetBSD or Solaris. User domains may either be unmodified open-source or proprietary operating systems, such as Microsoft Windows (if the host processor supports x86 virtualization, e.g., Intel VT-x and AMD-V), or modified, para-virtualized operating system with special drivers that support enhanced Xen features.
On x86 Xen with a Linux dom0 runs on Pentium II or newer processors. Xen boots from a bootloader such as GNU GRUB, and then usually loads a paravirtualized host operating system into the host domain (dom0).
Read more about this topic: Xen
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