Xen Project boots from a bootloader such as GNU GRUB, and then usually loads a paravirtualized host operating system into the host domain (dom0). User domains may either be traditional operating systems, such as Microsoft Windows under which privileged instructions are provided by hardware virtualization instructions (if the host processor supports x86 virtualization, e.g., Intel VT-x and AMD-V), or paravirtualized operating systems whereby the operating system is aware that it is running inside a virtual machine, and so makes hypercalls directly, rather than issuing privileged instructions. The dom0 domain is typically a version of Linux or BSD. From the dom0 the hypervisor can be managed and unprivileged domains ('domU') can be launched. 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. Xen Project runs in a more privileged CPU state than any other software on the machine, except for Firmware. Xen Project is currently available for the IA-32, x86-64 and ARM instruction sets. The Xen Project community develops and maintains Xen Project as free and open-source software, subject to the requirements of the GNU General Public License (GPL), version 2. Originally developed by the University of Cambridge Computer Laboratory and is now being developed by the Linux Foundation with support from Intel, Citrix, Arm Ltd, Huawei, AWS, Alibaba Cloud, AMD, Bitdefender and epam. Xen (pronounced / ˈ z ɛ n/) is a type-1 hypervisor, providing services that allow multiple computer operating systems to execute on the same computer hardware concurrently.

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