Hypervisor Types

The key to virtualization is the concept of a hypervisor, which is a software layer that sits between the host physical hardware and the guest virtual machines. The hypervisor facilitates and manages access of the virtual machines to the physical hardware resources.

Virtualization hypervisors come in two distinct flavors. The first, Type 1, enables virtualization to occur directly within existing operating system. Good examples of a Type 1 hypervisor are the Microsoft Virtual PC or VMware Workstation products. These are applications that run in an existing operating system on a workstation or server, and they enable the user to run virtual machines in the operating system. The hypervisor in these instances runs on top of the host operating system, as depicted in Figure 29.1.

Figure 29.1. Type 1 hypervisor.

The second type of hypervisor, Type 2, is far more efficient than Type 1, because it is installed directly onto the physical hardware, as shown in Figure 29.2. This is the type of hypervisor in Microsoft Hyper-V and VMware vSphere products. Type 2 hypervisors are more efficient because there is no need to have the hypervisor first pass through the host operating system before addressing resources for the virtual machine guests.

Figure 29.2. Type 2 hypervisor.