Hypervisor Types

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

Virtualization hypervisors come in two distinct flavors. The first, Type 1, allows virtualization to occur directly in an 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 allow 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 25.1.

Figure 25.1 Type 1 Hypervisor

The second type of hypervisor, Type 2, is far more efficient than Type 1 because it actually operates at a level directly above the physical hardware, as shown in Figure 25.2. This is the type of hypervisor product is used in Microsoft Hyper-V or 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 25.2 Type 2 Hypervisor