Virtualization is a technology that allows the physical machine resources to be shared among different Virtual Machines (VMs). It is provided by a software layer called hypervisor or Virtual Machine Monitor (VMM). The hypervisor abstracts the hardware from the operating system permitting multiple operating systems to run simultaneously on the same hardware. Many different hypervisors – both open source and commercial – exist today and are widely used in parallel and distributed computing. While the goals of these hypervisors are the same, the underlying technologies vary.