There????????s a new wind of change in the IT industry today. It????????s called virtualization????????guest operating system (OS) or hardware virtualization that is. Guest OS virtualization is a software layer that provides the ability to simulate a physical machine on top of an existing operating system running on a hardware host. This ability to run one or more virtual machines on top of one physical host opens up several possibilities in the industry. It is now much easier to create testing, training or development environments, it is easier to create secure virtual desktop environments as well as rely on virtualization to reduce the number of physical boxes to manage, and virtualization opens up vast possibilities in business continuity. Virtualization software first emerged in order to let users run a simulated operating system on top of another operating system. Users of the Apple Macintosh for example, were able to create virtual machines running Microsoft Windows on their Macs, giving them access to the thousands of programs that run on this platform but not on theirs. Over the years, virtualization software matured into a product of its own and spawned a multi-million dollar industry. Today you can run several different types of virtualization software. In fact, the industry has developed four different types of virtualization software: ??????? Server virtualization: Allows users to run a server operating system inside a virtualization layer. Server virtualization is a powerful engine for server consolidation since one physical machine can run multiple virtualized server operating systems (OS). ??????? Desktop virtualization: Allows users to run a desktop operating system inside a virtualization layer. Desktop virtualization makes it easier to control desktop environments and to provide training tools, testing environments, and secure remote access. ??????? Software virtualization: Allows users to create a virtualization layer that "sandboxes" software installations on the operating system. The software still works as usual, but it does not change the operating system that lies beneath it in any way. Software virtualization provides a much easier model for software distribution and license management. ??????? Presentation virtualization: a new term that is applied to an old technology: Terminal Services or Remote Desktops. Basically, the presentation layer of a desktop or an application is made available to a remote user without making any changes on their system. The software actually runs on a remote system, but its screens are displayed on the local system. Of these four, server and desktop virtualization are the most widely adopted. Both fall within the guest OS virtualization category. Presentation virtualization is also quite popular, but most people don????????t know it by its new name. Software virtualization, though it has been around for several years, is just now breaking into datacenters as IT professionals realize its strong potential for cost savings.