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== What is Virtualization? ==
In a traditional computing model, a computer system typically runs a single operating system. For example, a desktop computer might run a copy of Windows XP or Windows Vista, while a server might run Linux or Windows Server 2008. The concept of virtualization, as it pertains to this book, involves the use of a variety of different technologies to allow multiple and potentially varied operating system instances to run concurrently on a single physical computer system, each sharing the physical resources of the host computer system (such as memory, network connectivity, CPU and storage). Within a virtualized infrastructure, a single physical computer server might, for example, run two instances of Windows Server 2008 and one instance of Linux. This, in effect, allows a single computer to provide an IT infrastructure that would ordinarily required require three computer systems.
== Why is Virtualization Important? ==
* '''Operating system market fragmentation''' - In recent years the operating system market has increasingly fragmented with Microsoft ceding territory to offerings such as Linux and Apple's Mac OS. Enterprises are now finding themselves managing heterogeneous environments where, for example, Linux is used for hosting web sites whilst Windows Server is used to email and file serving functions. In such environments, virtualization allows different operating systems to run side by side on the same computer systems. A similar trend is developing on the desktop, with many users considering Linux as an alternative Microsoft Windows. Desktop based virtualization allows users to run both Linux and Windows in parallel, a key requirement given that many users looking at Linux still need access to applications that are currently only available on Windows.
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<td width="20%">[[Xen Virtualization Essentials|Previous]]<td align="center">[[Xen Virtualization Essentials|Table of Contents]]<td width="20%" align="right">[[An Overview of Virtualization Techniques|Next]]</td>
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<td width="20%">Table of Contents<td align="center"><td width="20%" align="right">An Overview of Virtualization Techniques</td>
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