This glossary is intended to define the terms used in this Installation Guide.



The term bare-metal refers to the underlying physical architecture of a computer. Running an operating system on bare-metal is another way of referring to running an unmodified version of the operating system on the physical hardware. Examples of operating systems running on bare metal are dom0 or a natively installed operating system.



Also known as the Host or host operating system.

dom0 refers to the host instance of Red Hat Enterprise Linux running the Hypervisor which facilitates virtualization of guest operating systems. Dom0 runs on and manages the physical hardware and resource allocation for itself and the guest operating systems.


domU and Domains are both domains. Domains run on the Hypervisor. The term domains has a similar meaning to Virtual machines and the two are technically interchangeable. A domain is a Virtual Machine.


domU refers to the guest operating system which run on the host system (Domains ).


Full virtualization

You can deploy Red Hat Virtualization in one of two choices: full virtualization or para-virtualization. Full virtualization provides total abstraction of the underlying physical system (Bare-metal ) and creates a new virtual system in which the guest operating systems can run. No modifications are needed in the guest operating system. The guest operating system and any applications on the guest are not aware of the virtualized environment and run normally. Para-virtualization requires a modified version of the Linux operating system.

Fully virtualized

See Full virtualization.


Guest system

Also known as guests, virtual machines or domU.


Hardware Virtual Machine

See Full virtualization


The hypervisor is the software layer that abstracts the hardware from the operating system permitting multiple operating systems to run on the same hardware. The hypervisor runs on the host system allowing virtual machines to run on the host's hardware as well.


The host operating system, also known as Domains.

The host environment runs the software for Fully virtualized and Fully virtualized guest systems.



Short for input/output (pronounced "eye-oh"). The term I/O is used to describe any program, operation or device that transfers data to or from a computer and to or from a peripheral device. Every transfer is an output from one device and an input into another. Devices such as keyboards and mouses are input-only devices while devices such as printers are output-only. A writable CD-ROM is both an input and an output device.


The Intel Itanium® processor architecture.


Kernel-based Virtual Machine

KVM is a Full virtualization kernel module which will be incorporated into future releases of Red Hat Enterprise Linux. KVM is presently available in the fedora Linux distribution and other Linux distributions.



Logical Unit Numbers(LUN) is the number assigned to a logical unit (a SCSI protocol entity).



See also Relocation

Migration refers to the process of moving a para-virtualized guest images from one Red Hat Virtualization server to another. This other server could be on the same server or a different server, including servers in other locations.

MAC Addresses

The Media Access Control Address is the hardware address for a Network Interface Controller. In the context of virtualization MAC addresses must be generated for virtual network interfaces with each MAC on your local domain being unique.



Para-virtualization uses a special kernel, sometimes referred to as the xen kernel or kernel-xen to virtualized another environment while using the hosts libraries and devices. A para-virtualized installation will have complete access to all devices on the system. Para-virtualization is significantly faster than full virtualization can can be effectively used for load balancing, provisioning, security and consolidation advantages.

As of Fedora 9 a special kernel will no longer be needed. Once this patch is accepted into the main Linux tree all linux kernels after that version will have para-virtualization enabled or available.

Para-virtualized drivers

Para-virtualized drivers are device drivers that operate on fully virtualized linux guests. These drivers greatly increase performance of network and block device I/O for fully virtualized guests.



Another term for Migration usually used to describe moving a virtual machine image across geographic locations.


Virtual cpu

A system running Red Hat Virtualization has a number of virtual cpus, or vcpus. The number of vcpus is finite and represents the total number of vcpus that can be assigned to guest virtual machines.

Virtual machines

A virtual machine is a software implementation of a physical machine or programming language (for example the Java Runtime Environment or LISP). Virtual machines in the context of virtualization are operating systems running on virtualized hardware.

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