The "Flavors" of Desktop Virtualization

Virtual Desktop

Deciphering the Many 'Flavors' of Desktop Virtualization

By Barbara DePompa

A range of virtualization software and delivery technologies promises to enable a new desktop computing model, which market researchers, including IDC, maintain may overcome many of the current limitations associated with distributed desktop computing.

Currently, there’s no one-size-fits-all desktop virtualization solution. Rather, each desktop virtualization supplier offers a number of options to deliver desktop capabilities to users. “What they all share is that they’re different from traditional desktop computing,” said Ian Song, Research Analyst for IDC in Framingham, Mass.

Although client virtualization technologies have been maturing during the past two years, significant growth has yet to be realized, largely due to complexity and a lack of one-stop shopping for an entire spectrum of desktop virtualization technologies. Still most research firms, including IDC, predict an upswing in the adoption of desktop virtualization solutions in the coming months Suppliers continue to work on improving and simplifying their solutions, and IDC just released a report written by Song, entitled 2010 Virtual Client Computing Taxonomy and Guidance, which is designed to help customers understand the various technologies involved, and how best each organization can extract value from the range of virtualized solutions currently available.

IDC uses the umbrella term client virtualization to describe all technologies associated with virtualizing the end user computing experience, as opposed to the widely acknowledged desktop virtualization, which Song said describes only the technologies used to virtualize end user desktops. While the entire exercise seems an enormous semantic challenge, IDC has categorized client virtualization into four primary components:

Desktop Virtualization – uses hypervisor technology (a type of software that allows multiple operating systems to run concurrently on a host computer) to decouple an operating system from its host hardware, and isolate the specific client environment from other operating systems running on a physical device. This model is generally recognized as virtual desktop integration (VDI). Within this category, Song maintains there are two types of desktop virtualization technologies:

• Centralized Virtual Desktop, a form of server based computing that uses a ‘server grade’ hypervisor to host multiple unique and isolated client operating systems aboard a single server or group of servers in the datacenter. Virtual desktops are delivered to end-users devices via the network.

• Distributed Virtual Desktop, which runs on a ‘client grade’ hypervisor, in other words a virtual machine resides on the local client hardware, such as a laptop computer.

Application Virtualization – software technology that detaches an application from the underlying operating system. Song maintains that a virtualized application doesn’t need to be installed in the traditional sense, but can be executed just as a natively installed application. The environment that encapsulates a virtualized application is typically called a sandbox or virtualized container, designed to fool the enclosed application into believing it’s directly interfacing with the operating system and all associated resources. Virtual applications can either be executed on a PC, leveraging processing power from a traditional PC, or executed on the server-side, then streamed to an endpoint device, typically to a thin client or stateless PC. There are also managed services based on application virtualization that allow administrators to allow/disallow virtual application to run locally, set application expiration, control provisioning of applications according to user rights and grouping and enforce license compliance. Song explained that many organizations are currently evaluating application virtualization to provide application compatibility when migrating from Windows XP to Windows 7.

Virtual User Sessions – a mature server based computing model that creates a shared environment to host multiple users from a single operating system. Each user gets access to their own profile and instance of installed applications. Virtual user sessions can be delivered to any end user device via the network, the only requirement for the device would be support for the protocol rendering the virtual environment. The technology can also be used to deliver specific applications to users, allowing users to connect directly to a specific application rather than an entire desktop. Because virtual user sessions require network connectivity to operate, Song said this works well for sensitive applications, where administrators can constantly monitor and regulate usage to ensure compliance. The limit on this technology is that it can only use a single copy of the operating system, forcing users to share a single environment. This creates a security flaw in that any devices connected at end points would be available for all connected users. Because virtual user sessions don’t require an existing hypervisor infrastructure, organizations currently not utilizing server virtualization can implement a virtual user session solution without investing heavily in remediating the data center. The technology is currently offered by Microsoft as Remote Desktop Server or Citrix as XenApp, Song said.

User Virtualization – decouples the end user personal data and settings from the underlying operating system and applications, therefore creating portable user identity that can be applied to any connected end points. The traditional application of this technology has been mainly Microsoft Roaming Profile and Folder Redirection. With the emergence of virtual desktops, and the promise of ‘anywhere, any device’ access to the desktop environment, user virtualization solutions are becoming increasingly relevant, he said. Upcoming solutions are expected to offer more advanced user virtualization that can not only decouple user profiles, but personal applications as well. User virtualization can help organizations achieve cost savings by leveraging dynamic desktops, in which one golden image is used to dynamically assemble multiple personalized desktops by applying layering technologies enabled by user virtualization. The result of dynamic virtual desktops is reduced storage requirement and management overhead, driving down the cost of ownership. Most desktop virtualization vendors already have certain user virtualization capabilities built-in, although certain user segments, such as knowledge workers, might require more advanced user virtualization solutions.

And while the descriptions above still may not fully eliminate confusion about the various types of desktop virtualization technologies, there are other components involved in the selection of a desktop virtualization solution as well, including delivery technologies and the hardware to be used at endpoints. Delivery technologies include the protocols used for network communications, and perhaps even a connection broker, which is used to manage a pool of connections such as remote desktop computers or virtual machines. Song explained that some third party vendors offer connection broker solutions that can translate different networking protocols, supporting multiple platforms at once. Finally, end user hardware can range from full PCs, to repurposed or stateless PCs, thin clients to something called a zero client – an ultra thin client with no embedded operating system. There are even mobile clients that can be hardware or software based for use in notebook PCs and mobile phone devices. More detailed information including breakdowns of the leading industry supplier offerings is available at