Virtual Infrastructure Professionals Ltd

Virtual Machine

A representation of a real machine using software that provides an operating environment which can run or host a guest operating system.

Guest Operating System

An operating system running in a virtual machine environment that would otherwise run directly on a separate physical system.

Virtual Machine Monitor

Software that runs in a layer between a hypervisor or host operating system and one or more virtual machines that provides the virtual machine abstraction to the guest operating systems. With full virtualisation, the virtual machine monitor exports a virtual machine abstraction identical to a physical machine, so that standard operating systems (e.g., Windows 2000, Windows Server 2003, Linux, etc.) can run just as they would on physical hardware.

Hypervisor

A thin layer of software that generally provides virtual partitioning capabilities which runs directly on hardware, but underneath higher-level virtualisation services. Sometimes referred to as a “bare metal” approach.

Hosted Virtualisation

A virtualisation approach where partitioning and virtualisation services run on top of a standard operating system (the host). In this approach, the virtualisation software relies on the host operating system to provide the services to talk directly to the underlying hardware.

Para-virtualisation

A virtualisation approach that exports a modified hardware abstraction which requires operating systems to be explicitly modified and ported to run.

Virtualisation Hardware Support

Industry standard servers will provide improved hardware support for virtualisation. Initial hardware support includes processor extensions to address CPU and some memory virtualisation. Future support will include I/O virtualisation, and eventually more complex memory virtualisation management.

Hardware-level virtualisation

Here the virtualisation layer sits right on top of the hardware exporting the virtual machine abstraction. Because the virtual machine looks like the hardware, all the software written for it will run in the virtual machine.

Operating system–level virtualisation

In this case the virtualisation layer sits between the operating system and the application programs that run on the operating system. The virtual machine runs applications, or sets of applications, that are written for the particular operating system being virtualised.

High-level language virtual machines

In high-level language virtual machines, the virtualisation layer sits as an application program on top of an operating system. The layer exports an abstraction of the virtual machine that can run programs written and compiled to the particular abstract machine definition. Any program written in the high-level language and compiled for this virtual machine will run in it.