Server virtualization or Hardware virtualization or platform virtualization refers to the creation of a virtual machine that acts like a real computer with an operating system.

Virtual machines are based on the host/guest paradigm. Each guest runs on a virtual imitation of the hardware layer. This approach allows  creation of guests that use different operating systems. The guest has no knowledge of the host’s operating system because it is not aware that it’s not running on real hardware. It does, however, require real computing resources from the host. Those resources can then be allocated on the guest machines (# of CPUs, memory, disk space, network adapters and more…)

Some of the most popular virtualization software include Microsoft Hyper-V, VMWare VSphere, Citrix Xenserver and VirtualBox.