Xen is a hypervisor using a microkernel design that allows running multiple concurrent operating systems on the same hardware. One of the key features of Xen is that it is OS agnostic, meaning that any OS (with proper support) can be used as a host. Xen has a long history going back to the 90s when it was designed and the early 2000s when it was released. As a consequence of this, many of the assumptions and virtualization techniques backed into it are now superseeded by new hardware features, that make virtualization more transparent from an OS point of view.