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In computing, Desktop Virtualization involves separating the physical location where the PC desktop resides from where the user is accessing the PC. A remotely accessed PC is typically either located at home, at the office or in a data center. The user is located elsewhere, perhaps traveling, in a hotel room, at an airport or in a different city. The desktop virtualization approach can be contrasted with a traditional local PC desktop, where the user directly accesses the desktop operating system and all of its peripherals physically (using the local keyboard, mouse and video monitor hardware directly).

When a desktop is virtualized, its keyboard, mouse and video display (among other things) are typically redirected across a network via a desktop remoting protocol (such as RDP, ICA, VNC, etc). The network connection carrying this virtualized desktop information is known as a "desktop access session".

Virtually any kind of end-user device can be used to remotely access a virtualized PC desktop, including thin clients, notebook PC's and even a PDA. Once a desktop is virtualized, it becomes accessible over any suitable network connection, on any device with similar characteristics.

There are four (4) distinct classes of desktop virtualization today:

1. Single Remote Desktop - in this model, a single desktop PC is accessed remotely across a network connection using remote PC access software, such as GoToMyPC, WebEx, PCAnywhere, Windows Remote Desktop, VNC and other similar methods.
2. Shared Desktops - in this model, a multi-user server PC environment like Citrix and Terminal Services are used to host many users who all "share" a common PC desktop environment together on a server machine. In this case, it's generally possible to host up to a few hundred desktop sessions on powerful server hardware.
3. Virtual Machine Desktops - in this model, virtual machine technology is used to host multiple instances of a standard, single-user desktop PC operating system (e.g., Windows XP) on a server machine. In this case, it's generally possibly to host a few dozen desktop sessions on powerful server hardware.
4. Physical PC blade Desktops - in this model, individual "client blade" PC's are used host multiple independent user sessions, each one running on its own physical PC blade. In this case, it's possible to host as many client PC blades as you have rack space, power and data center space to accommodate.

Each of these virtualized desktop models have their specific advantages and limitations. The most common case is a user simply needing direct access to a single PC machine's desktop from a remote location over a network (often the Internet). When many user desktops need to be hosted and managed centrally, that's where the Shared, VM and Physical Desktop models come into play.

Desktop Virtualization is a growing marketplace, driven by many different factors, including people's needs to work remotely for various reasons (e.g., tele-working, mobile sales, outsourcing), and companies needs to maintain control over their computing assets and intellectual property that's running on business desktops.

Running user desktops (and applications) centrally provides significant value and benefits over the traditional local PC desktop model, including improved security by keeping desktops in secure data centers, lowering management costs through centralization, and the ability to effectively share PC compute power across many users. Since desktop virtualization involves running the PC desktop experience across various networks, a number of important security and performance issues arise, which require careful attention and planning.