Hypervisor

Hypervisor means supervisor of supervisor – a strong supervisor. It is hardware or software, which allows to create and control one or more virtual systems. Hypervisor are also known as Virtual Machine Monitor(VMM).

A computer, on which Hypervisor runs, is called as “Host Machine”. The operating system is referred as “Host OS”. Hypervisor allows to create one or more virtual systems on top of Host Machine’s hardware. Each virtual system may have different operating system. Such operating system is referred as “Guest OS”.

The need to use hardware more efficiently gave rise to the Hypervisors. They emulate the underlying hardware for the virtual machines as per the configuration.

It is easy to confuse VMs with Containers, however, there is clear differentiation between these two entities. VMs bundle operating systems within them whereas Containers do not.

Types of Hypervisor

• Bare-Metal – This layer is installed directly at hardware level and doesn’t have any Host OS at all. It directly allows to install guest operating systems. These type of Hypervisors obviously give speed and efficiency as they work directly off the hardware. They give deterministic response times, smaller memory footprint and fine grained control.
• Hosted – These reside on top of host operating system. These are preferred where speed has lesser consideration, but manageability requirement is higher. Additionally, these are available on a wider range of underlying hardware and are  easier to setup and install.

Examples of Hypervisor:

Opensource XEN, Citrix XenServer, VMWare’s ESX,

References:

• Wikipedia Link
• Slide Deck explaining the concept

Related Keywords:

Containers, Virtualization, Cloud, Paravirtulaization