Specialized execution environments.

Virtualization has become popular (again) as a means of consolidating multiple operating systems (OSes) onto a smaller set of hardware resources. The roles of OSes in such environments have changed. Whereas normally an OS provides balance between the demands of application and hardware support, in the world of virtualization it can be beneficial to split these roles. One OS may support a particular application set and use other OSes to interact with physical hardware. The hypervisor, or virtualization layer, provides communication facilities for the inter-OS communication needed to support such a deployment model.