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1.2 Understanding Virtualization
Modes
Guest operating systems are hosted on virtual machines in either full virtualization
mode or paravirtual mode. Each virtualization mode has advantages and disadvantages.
• Full virtualization mode lets virtual machines run unmodified operating systems,
such as Windows* Server 2003 and Windows XP, but requires the computer running
as the VM Host Server to support hardware-assisted virtualization technology, such
as AMD* Virtualization or Intel* Virtualization Technology.
Some guest operating systems hosted in full virtualization mode, can be configured
to run the Novell* Virtual Machine Drivers instead of drivers originating from the
operating system. Running virtual machine drivers improves performance dramat-
ically on guest operating systems, such as Windows XP and Windows Server 2003.
For more information, see Chapter 13, Virtual Machine Drivers (page 105).
• Paravirtual mode does not require the host computer to support hardware-assisted
virtualization technology, but does require the guest operating system to be modified
for the virtualization environment. Typically, operating systems running in paravir-
tual mode enjoy better performance than those requiring full virtualization mode.
Operating systems currently modified to run in paravirtual mode are referred to as
paravirtualized operating systems and include SUSE Linux Enterprise Desktop 11
and NetWare® 6.5 SP8.
1.3 Xen Virtualization Architecture
The following graphic depicts a virtual machine host with four virtual machines. The
Xen hypervisor is shown as running directly on the physical hardware platform. Note,
that the controlling domain is also just a virtual machine, although it has several addi-
tional management tasks compared to all other virtual machines.
Introduction to Xen Virtualization 5