Virtualization describes a technology in which an application, guest operating system (guest OS) or data storage is abstracted away from the true underlying hardware or software. A key use of virtualization technology is server virtualization, which uses a software layer — called a hypervisor — to emulate the underlying hardware. This often includes the CPU’s memory, input/output (I/O) and network traffic. Hypervisors take the physical resources and separate them so they can be utilized by the virtual environment. They are able to sit on top of an OS or they can be directly installed onto the hardware. The latter is how most enterprises virtualize their systems.