How to install Xen hypervisor on unused old hardware

Xen is a bare metal hypervisor, meaning that you must prepare a bare machine to install and run Xen. KVM is a little different – you can add it to any machine already running Linux. This tutorial describes how to install and configure Xen hypervisor on unused hardware. This procedure uses Debian Jessie (their testing distribution) as the host OS (also known as Dom0).