A hypervisor or virtual machine monitor (VMM) is a piece of computer software, firmware or hardwarethat creates and runs virtual machines.
A computer on which a hypervisor is running one or more virtual machines is defined as ahost machine. Each virtual machine is called aguest machine. The hypervisor presents the guest operating systems with avirtual operating platformand manages the execution of the guest operating systems. Multiple instances of a variety of operating systems may share the virtualized hardware resources.
The hypervisor installed on the server hardwarecontrols the guest operating system running on the host machine. Its main job is tocater to the needs of the guest operating system and effectively manage it such that the instances of multiple operating systems do not interrupt one another.
Hypervisors can be divided into two types:
Type 1 Hypervisors : Also known as native or bare-metal hypervisors, these run directly on the host computer’s hardware to control the hardware resources and to manage guest operating systems. Examples of Type 1 hypervisors include VMware ESXi, Citrix XenServer and Microsoft Hyper-V hypervisor.
Type 2 Hypervisors : Also known as hosted hypervisors, these run on an operating system environment. Type-2 hypervisors abstract guest operating systems from the host operating system. In this type, the hypervisor runs as a distinct second layer while the operating system runs as a third layer above the hardware. Examples , VMware Workstation,VMware PlayerandVirtualBox .