Hypervisor
Problem Statement :
In cloud environment there are multiple ways of providing the infrastructure or compute machines(instances). Here are two choices
1. A complete machine been provided (Baremetal)
2. A machine been shared by different tenants using different VM. (Tenancy)
Tenancy required to run different operating systems on a single machines, called host machine and software or mechanism which control execution of different systems on a single machine is called hypervisor. Evolution of hardware also leads to increase in resources for the systems, where more power (CPU and Memory) are now been fused to new machines and these machines are capable to run a lot task simultaneously.
There are two kind of hypervisors, one is bare metal hypervisor, Where the hypervisor directly interact with the hardware. Multiple OS then run on the top of the hypervisor, Other kind of hypervisor which run on the top of OS, called hosted hypervisor.
Hosted hypervisor run over the OS, these hypervisor use main OS to interact and use hardware resources of system, and then allow other systems/OS to run over it.
1.2 Native or Bare-metal Hyper-visor
Baremetal hypervisor directly run over the host system and control everything, there are multiple of such hypervisor are there few of them are like power from IBM, Oracle VM Server. Here hypervisor is the system which interact directly with the hardware and provide the interface over which OS run and these OS interact with the hypervisor for basic demands like IO/CPU and network.
Hypervisor then control and provide everything to these machines, which in turn runs as a separate systems.
1.3 Host Hyper-visor
This hydpervisor run on the OS, OS is premiere run over the machine and control the resources. Hypervisor run over the OS and then use resources of OS. Example are VMware which run over the system and next set of OS or system run over the hypervisor.
Sometime there is no clear distinction between the two, sometime these two type are quite merged like linux kernel based virtualisation.
