Managing PCs has always been painful, but the job has gotten considerably nastier thanks to an endless parade of application upgrades, operating system patches, and anti-threat updates. Even with network-based installation and patch management tools to ease the burden, IT spends far too much time at the desktop itself, dealing with shenanigans involving personal software, multiple versions of Java or ActiveX controls, driver or DLL conflicts, malware infections, misconfigured hardware, and more.

The promise of desktop virtualization technology is to centralize applications at the datacenter to make them easier to manage and provision -- stretching hardware resources and keeping nagging software conflicts to a minimum in the bargain. In some cases, the same technology helps accomplish all three, bringing greater control and flexibility to IT without users mourning the loss of "their" beloved desktops.

At first blush, desktop virtualization sounds a lot like terminal services such as those provided by Citrix Systems, where servers run the applications and give users remote access. All the user's terminal or PC does is present the updated screen display and permit input via keyboard and mouse.

Desktop virtualization, on the other hand, is a new way of delivering the individual PC environment that white-collar workers demand and love. In essence, servers host an entire desktop environment specific to each user.

The early versions of desktop virtualization were blade servers such as those offered by ClearCube Technology and IBM that simply moved the processing guts of a PC to the datacenter and left the input and display at the user's desk. But the latest versions use the PC at the user's desk for much of the processing. Dubbed "desktop streaming," this approach retains the benefits of central management without throwing away the desktop's power. The needed code is streamed to disk and memory cache for just that session, ensuring that there's nothing for the user to mess up or alter.

A few providers go beyond desktop streaming to application streaming, where IT can send out the runtime cache for individual apps as needed. This reduces the number of unique user images to maintain and provides better insight into which application licenses are really needed.

Building a better thin client

The greatest benefit of desktop virtualization is the ability to provision PCs and other client devices with software from a central location. IT can manage a large number of enterprise clients from the datacenter, rather than at each user's desk, reducing on-site support and increasing control of application and patch management.

At its simplest, virtualization on the application server side reduces hardware costs by letting one server provision multiple desktop clients, rather than having one server per desktop client, says John Humphreys, an IDC analyst. And virtualization also adds the ability to move desktop environments and hosted applications as needed for load-balancing or fail-over. To make existing terminal services and blade systems work with virtual machines, established providers such as Citrix and ClearCube have developed broker technology to let IT manage the mapping to virtual resources.

Citrix, ClearCube, and Wyse Technology now support the use of VMware and Microsoft virtual machines on blades and other application servers. VMware also offers VDI (Virtual Desktop Infrastructure software), which makes server-hosted virtual machines accessible to users through the RDP (Remote Desktop Protocol).

Bell Canada uses VDI to provision desktops to call-center users, letting them work in other locations or even at home without burdening IT support, notes Martin Quigley, senior solutions adviser for adaptive infrastructure at Bell Systems & Technology, which manages Bell Canada's call centers. "RDP is quite thin," he notes, so it does not burden the network. But Quigley looks forward to the next release of VMware's underlying ESX technology, which will support load balancing across servers, making it easier to maintain performance levels as user demands change. (Currently, this is a manual process.)

At Duncan Regional Hospital in Duncan, Oklahoma, the number of desktops more than doubled to about 500 in the past two years. Rather than lobby for money to hire more desktop support techs, CIO Roger Neal decided to deploy ClearCube thin clients and keep the physical management in a central location -- and get more from his existing staff. When ClearCube began supporting VMware virtual machines in 2006, Neal began reconfiguring his blade servers to run three virtual machines per blade, so he wouldn't need more blades as the demand for desktops increased. He also saw desktop support calls drop by 40 percent, which he attributes to centralized PC management.

Streaming to the desktop

Virtualization at the application host server can make thin clients more efficient to deploy, but many organizations are wedded to having real PCs at users' disposal despite the support costs. Desktop streaming is emerging as one of the most efficient ways to support this model without incurring the usual bloated desktop support costs.

A growing number of vendors -- including Ardence, Propero, Stream Theory and Wyse -- offer desktop streaming software that provisions the entire desktop environment from a server to a desktop PC (or thin client).

Altiris, AppStream, and Microsoft (through its recent acquisition of Softricity) have pushed the concept to the next level, streaming applications rather then a complete desktop environment. This allows greater flexibility in what is provisioned, because IT can create a basic operating system image and then individual images for each application, and combine them as needed on the fly. You don't need a separate desktop image for each combination of applications.

With both desktop and application streaming, the provisioned operating system and applications use the client's local resources, without the overhead of permanent installation on the client. For example, financial services firm Russell Investments Group saw application deployment shrink from four weeks to 1.5 weeks after it began using Microsoft's SoftGrid, says Greg Nelson, an IT analyst at the company.

Typically, a set of stub services is transferred to the local cache at connection time, and other resources are streamed as needed. "When you run an application, you need only 15 to 20 percent to start using it, so it can be network-delivered," says David Grescher, director of marketing for SoftGrid at Microsoft.

Streaming does delay initial application access, acknowledges Bill Washburn, operations analyst at California State University at San Marcos, which uses Altiris' technology. "But once the application is installed, people say it's the best they've ever seen it run," he says.

Russell Investments' Nelson says that although desktop and application streaming should theoretically use more network resources than terminal services do, that's not always the case. For example, printing and working with large files can swamp the network in a traditional terminal services architecture. Desktop and application streaming can avoid that by using local printers and local storage.