Hardware Reference
In-Depth Information
create and manage a virtual machine (VM), which is a section of RAM and hard disk space that is set
aside for use by an operating system and its applications. Once a VM is created and started, the user
can install an operating system supported by the VMM, install any utilities designed to make the
operating system work better inside the VM, and can use the VM as if it is the only operating system
running on the hardware. The disk space used by a VM is usually dynamic, expanding from a small
size to a pre-set maximum only as needed, and the RAM allocated to a VM is available for other
processes when the VM is closed.
In hypervisor/client virtualization, the virtual machine manager (VMM) runs directly on the hardware,
enabling VMs to go through fewer layers of emulation for faster performance than with host/guest
virtualization. This type of virtualization is sometimes referred to as Type 1 or bare-metal
virtualization. This is the type of virtualization performed by Microsoft Hyper-V and most server-
class virtualizers.
In host/guest virtualization, a host operating system runs a virtual machine manager (VMM) program.
The VMM is used to create and manage operating systems loaded as guests. In this type of
virtualization, the connections between hardware and the virtual machine must pass through two
layers: the device drivers used by the host operating system and the virtualized drivers used by the
VMM. The multilayered nature of host/guest virtualization makes this type of virtualization relatively
slow. It is also referred to as
Type 2 virtualization
, and Microsoft Virtual PC and Windows Virtual
PC are examples of this type of virtualization.
Most virtualization programs for Windows-based PCs, such as Microsoft Virtual PC 2004 and 2007,
use host/guest virtualization. To enable virtualization to run faster and make virtualization more
useful, both Intel and AMD have added hardware-assisted virtualization support to their processors.
The original edition of Windows Virtual PC for Windows 7 required the use of processors with
hardware-assisted virtualization support with the BIOS configured to enable this feature. Although the
current version of Windows Virtual PC does not require the use of processors with hardware-
assisted virtualization, this feature is highly desirable for any computer that will be used for
virtualization.
Note
Windows 8 Pro does not support Windows Virtual PC. Instead, it includes Hyper-V Client.
Enable it through the Add/Remove Features from Windows dialog in the Control Panel.
AMD-V
AMD refers to its hardware-assisted virtualization support as AMD-V, although BIOS setup
programs might also identify it as VMM or virtualization. Support for AMD-V is almost universal
across its processors starting with models supporting Socket AM2 and their mobile counterparts up
through current processors for AM3+ and FM2 sockets.
Intel VT-x and VT-D
Intel refers to its hardware-assisted virtualization support as Intel VT-x. Intel supports VT-x on all of
its second-generation and third-generation Core i3/i5/i7 processors, and with certain models in older
product families. Intel processors with VT-D support also virtualize directed I/O for faster
performance of I/O devices in a virtualized environment.
VIA VT
