Hypervisor

A hypervisor is a software package which provides virtual machines.

There are two main types of hypervisors, classified by their level of abstraction from the physical hardware:

• Type 1 - 'native' hypervisors, which are operating systems which run directly on the bare machine
• Type 2 - 'hosted' hypervisors, which are applications which run under a general-purpose OS.

The Type 2 hypervisors, for example VMware Workstation or Oracle VirtualBox, run as an application within the host operating system, ex: as a Linux or Windows program. To minimize overhead, Type 1 hypervisors avoid the need for the host to run another operating system, and they instead run directly on the bare-metal hardware. Examples of Type 1 hypervisors include VMware ESXi, Microsoft Hyper-V, and KVM.

Early hypervisors were created by IBM, including CP/CPS and VM/370, which allowed for creating VMs of different operating systems on the mainframe.