Microsoft Virtualization Secrets

Understanding the Types of Hypervisor

Before looking at Hyper-V in detail, this section briefly expands on some of the content I introduced in Chapter 3. When I talk about hypervisors, I am referring to the technology that enables the deployment of virtual machines and their assets, such as an amount of memory, processor resource allocation, network access, and some virtual storage in the form of a virtual hard drive. Hypervisors do much more than this, but at a fundamental level this is their primary function. In addition to the hypervisor, there needs to be some kind of virtual machine manager that facilitates the creation and management of virtual machines that run on the hypervisor and provides insight into the state of the virtual machines.

There are two main types of hypervisor: type 1 and type 2. A type 2 hypervisor runs on top of an operating system that is installed on the physical hardware. This is commonly seen on desktop virtualization solutions such as Windows Virtual PC. Typically, these solutions are not very efficient because all operations have to run through the host operating system installed on the hardware, and virtual machines cannot directly access the processor’s ring 0, which is where kernel mode instructions are executed. The advantage is that no special hardware is required.

A type 1 hypervisor runs directly on the hardware, and the virtual machines and the management operating system (if there is one) sit on top of the hypervisor and access hardware ...