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→Kernel Level Virtualization
== Kernel Level Virtualization ==
Under kernel level virtualization a specially modified kernel is responsible for running and controlling the various virtual machines. Guest operating systems must have been compiled for the same hardware as the kernel in which they are running. Examples of kernel level virtualization technologies include user Mode Linux (UML) and KVM. The following diagram provides an overview of the kernel level virtualization architecture:
[[Image:kernel_level_diagram.jpg|center|Kernel Level Virtualization Diagram]]
== Hypervisor Virtualization ==
Under hypervisor virtualization a program known as a hypervisor runs directly on the hardware of the host system. The task of the hypervisor is to handle protected and privileged CPU requests from the virtual machines and also to act as an intermediary between the hardware resources and the virtual machines.
In addition to the virtual machines, an administrative operating system also runs on top of the hypervisor allowing the virtual machines to be managed by system administrators.
At the time of writing there are three different types of hypervisor based virtualization:
- ''Paravirtualization'' - Under paravirtualization the guest operating systems must be modified specifically to run on the hypervisor. This typically restricts support to open source operating systems such as Linux and excludes proprietary operating systems such as Microsoft Windows. The ability of the guest system to communicate directly with the hypervisor results in greater performance levels than other virtualization approaches.
- ''Full Virtualization'' - Full virtualization provides support for unmodifed guest operating systems. In this scenario, the hypervisor provides emulation to handle privileged and protected CPU operations made by unmodified guest operating systems. As a result of this emulation the performance levels are lower than those provided by paravirtualization.
- ''Hardware Virtualization'' - Hardware virtualization is a hypervisor based solution that leverages Intel VT and AMD-V CPU virtualization support, using features of these technologies to handle privileged and protected CPU operations of unmodified guests.
