Virtualization is an abstraction layer that decouples the physical hardware from the operating system. Linux provides a stable platform to run several virtual machines.

The consolidation of physical servers onto virtual machines can improve resource utilisation and flexibility, simplify backup procedures and free up data centre space by replacing legacy hardware. It allows multiple virtual machines, with heterogeneous operating systems to run in isolation, side-by-side on the same physical machine.

Each virtual machine has its own set of virtual hardware (e.g., RAM, CPU, NIC, etc.) upon which an operating system and applications are loaded. This is an efficient way to manage legacy systems like Microsoft Windows.

Telephony & Fax Server (PABX)	Application Server	Windows Terminal Server
Virtualization Server for Guest Systems
Linux Host System includes the file server, backup, email and proxy servers, etc.

Virtual Machines & Appliances

One advantage is that booting and restarting a virtual machine can be much faster than with a physical machine, since it may be possible to skip tasks such as hardware initialisation. Another use is to provide multiple users the illusion of having an entire computer, one that is their "private" machine, isolated from other users, all on a single physical machine.

Virtual machines are encapsulated into files, making it possible to rapidly save, copy and provision a virtual machine. Full systems (fully configured applications, operating systems, BIOS and virtual hardware) can be moved, within seconds, from one physical server to another for zero-downtime maintenance and continuous workload consolidation. The operating system sees a consistent, normalised set of hardware regardless of the actual physical hardware components.