Virtualization

Virtualization is the abstraction of computing resources from the physical hardware, making it possible to run several operating systems on one computer. The underlying virtualization platform where the hypervisor software resides is called a host, and the guests are virtual machines running on top of the hypervisor.

A hypervisor is a software between the physical hardware and the virtual machines. It manages virtual machines, providing its guests with a shared pool of resources for efficient use and fast methods to create new virtual machines, and migrate or remove existing guests.

There are two types of hypervisors. Type-1 hypervisors, also called bare-metal, are installed directly on the physical hardware. It is common when virtualizing servers, as no operating system lies between the hypervisor and physical hardware.

Type-2 hypervisors, also called hosted hypervisors, are more commonly used on personal computers. They are software running on top of an operating system like other applications. Since the underlying operating system has already configured the hardware, network, and storage, installing hosted hypervisor software is often quick and easy. In addition, virtual machines are isolated from each other, running on the hypervisor, making it possible to switch between different operating systems on the same computer without rebooting.

Virtual machines are running on top of a hypervisor; they have each been configured with resources they can request access to. The hypervisor has abstracted these resources, as all guests share physical resources on the device on which the hypervisor resides. It is the hypervisor that manages the virtual machines.

A virtual machine is flexible, as its physical form is a set of files, configuration file, and virtual disk files. These can easily be modified; it is possible to back up a server by copying the virtual machine files.