This is Part 2 of a two-part article. Part 1 was published on Friday.

Simplifying management

One big advantage of streaming is that IT has fewer images to maintain. That benefit applies in spades to application streaming products from Altiris and Microsoft.

For example, CSU's Washburn says that Altiris' Software Virtualisation Solution solves a long-standing annoyance with SPSS's statistical software. Each year, a new license key is issued and must be updated at every user's desktop. But with Altiris' software, Washburn simply updates the server copy, which is provisioned to users automatically when they call the application.

Although the technologies from Ardence, Propero, Stream Theory and Wyse centralise applications and data, they also let users store data locally as well (a PC's C drive is remapped to become its D drive when their software runs). Moreover, because Altiris' and Microsoft's application streaming tools let you set up applications in their own virtual layer or session, IT can avoid the regression testing across the whole application set whenever a program is modified or added, says Russell Investments' Nelson.

With the solutions offered by Altiris, AppStream, and Microsoft, the client PC can have its own operating system and applications installed, while the server pushes centrally provisioned applications into local desktop caches. In this fashion, IT can distribute resources selectively. For example, Russell's Nelson installs Windows along with applications that act as extensions to the operating system (such as Adobe Acrobat Reader, Apple QuickTime, and Java) on local PCs -- plus Microsoft Office and a few other frequently used applications -- on local PCs. Then he uses SoftGrid to provision other applications as streams.

This selective approach can also help balance performance, notes CSU's Washburn. Were Washburn to deliver everything as streams, it would take client PCs five minutes or more to boot up -- a non-starter. So he installs core applications on the PCs the old-fashioned way, using Altiris' remote deployment tools, and provisions less frequently used programs via application streaming.

Yet another variation is to combine application streaming with terminal services. At Alamance Regional Medical Center in Burlington, N.C., senior network administrator Andy Gerringer uses both Citrix and SoftGrid to provision desktops. Citrix is used in the usual manner to deliver server-based applications as individual sessions. But Alamance also uses Citrix to provide access to a SoftGrid desktop environment for terminal users. Essentially, the Citrix session runs the SoftGrid virtual machine. "SoftGrid and Citrix complement each other very well," Gerringer says.

Conflict resolution for applications

Application streaming comes with a significant side benefit: eliminating application conflicts. The application streaming tools from AppStream, Altiris, and Microsoft separate application-specific support files such as DLLs and libraries from the underlying operating system. Altiris separates just the support files, keeping the applications with the operating system, whereas AppStream and Microsoft keep each app and its support files together in one virtual layer or package.

These programs manage the communication among the layers and the underlying operating environment, so both Windows and its users think they are working on a single environment.

By separating each application into its own virtual layer (or package, as some call it), these products prevent software conflicts common with homeg-rown software and some commercial applications. And user-installed applications can't conflict with IT-provisioned applications in the virtual layers, says Microsoft's Grescher.

For example, before adopting SoftGrid, recalls Alamance's Gerringer, the medical centre had to maintain separate servers for ill-behaved apps, forcing users to switch among multiple systems from their terminals. "By summer 2005, the problem got too big to manage anymore the old way," Gerringer says.

The problem? Different versions of Java used by various specialty health care apps prevented simultaneous usage, as did the embedding of different versions of the Crystal Reports reporting tool in other applications. (If Crystal Reports 4 is running, Crystal 5 cannot run, for example.)

Now that Alamance uses SoftGrid, users get a unified desktop environment, with the ill-behaved apps corralled so they can no longer cause trouble.

The new reality of virtualisation

Desktop and application streaming require IT to think differently about tasks that they've done for years, notes Neal of Duncan Regional Hospital. "It takes a little more thought in the rollout," he says. For example, his support staff now has to keep an eye on the blades that serve the desktop environments, because a broken fan can cause them to overheat, knocking out multiple users in one blow. His staff also must monitor disk usage for each blade, because 80GB is shared among three users.

Virtualised desktops can be provisioned to specific client hardware, so a particular call-centre terminal always uses the same virtual machine on a specific blade. But they can also be provisioned to specific users, based on user log-in, so the client device running them could be anywhere. That can pose a challenge for setting up access to printers and departmental file servers, depending on how mobile users are, observes Bell's Quigley.

Quigley notes another issue that can puzzle support staff: Users connecting from home may not get their DNS address resolved properly, so IT tends to assign a fixed IP address to get around that issue. But the Windows virtual machines are rebooted each night to deal with memory leaks, and the IP address for that virtual machine might no longer match what is set up in the remote user's home system.

Nonetheless, early adopters all agree that these relatively minor issues are far outweighed by the benefits of central administration of fewer desktop images. As IDC's Humphreys says, "There are some really pragmatic reasons that this is taking off."