Once upon a time the primary function of terminal services software from either Citrix or Microsoft was to make it easier to manage multiple Windows implementations in a department by running all the instances of Windows on the server instead of the client.

But with the advent of Citrix XenApp 5 the convergence of terminal services and application virtualization is turning these technologies into a platform for building and delivering enterprise applications.

What makes XenApp5 intriguing is that it adds support for preferential load balancing that allows IT managers to give certain users guaranteed quality of service to certain applications. That capability is now also coupled with the ability to tightly couple sets of applications on the same server, which for the first time using Citrix technologies makes it easier to create, for example, an order entry system that runs across multiple applications being delivered via terminal services technology. Furthermore, these applications can now be delivered outside of a departmental network environment because the new version for XenApp adds support for HTTP.

What all this adds up to is a foundation for delivering virtual access to applications that can now be used to support any number of business processes as opposed to just delivering a single packaged Windows application via a server.

The real question that many IT organizations are really trying to sort out at the moment is what is the fundamental difference between application virtualization delivered via the server and the ability to create virtual machines on the desktop?

For the most part, application virtualization may well wind up being the preferred method for delivering packaged applications while IT organizations that have a need to run customized applications will need to run virtual machine software on the client to support them.

Whatever approach to virtualization of applications that IT organization decide to take it's pretty clear that virtualization technology is moving past the server pretty quickly. And while managing virtualization on the client may prove to be more challenging than on the server, the long term benefits of virtualization on the client in terms of return on investment should outweigh any of the initial concerns about installation and management headaches.