Client virtualization is an underlying theme in many recent industry announcements. In virtualization, the external interface of every service becomes unmoored from its implementation in particular physical platforms, operating systems, application frameworks and software components. Essentially, a client becomes virtualized when its GUI grows abstracted from the resources of the local access device, be it a PC, handheld or other computer. The virtualized client may rely on both local and remote network resources to render its interface, furnish its processing power, store its data, route its print jobs and handle other core client functions. Users remain blissfully unaware of what blend of distributed resources is actually driving their presentation experience.

Vendors are avidly exploring ways to virtualize client environments. Take Microsoft Windows Vista, for example. In the long, tortured ramp-up to the release of this client operating system, Microsoft has removed most of the new functional components - including security and file-system enhancements - that were supposed to make Vista worth waiting for. What's primarily left is a client virtualization technology called Windows Presentation Foundation (WPF), which allows the Windows GUI to be dynamically rendered, tailored and customized by applications, in keeping with a declarative markup syntax called Extensible Application Markup Language (XAML). Essentially, WPF/XAML enables a virtualized separation of the Windows presentation interface from the underlying application code.

Microsoft has even decoupled WPF/XAML from Vista, taking the Windows platform another step down the road to total virtualization. WPF/XAML - and all Vista features - also will be made available as retrofits for legacy Windows operating systems, including XP and Server 2003. Essentially, this new technology will become the virtualized presentation layer to all Windows versions.

There's even more to Microsoft's client virtualization story. Earlier this month, Microsoft announced its Windows Live strategy, under which operating system and application features will be provided as hosted software as a service. Essentially, Live is aimed at making free Microsoft-hosted services - such as e-mail, instant messaging, search, file sharing, VoIP, software delivery and RSS aggregation - integral to Microsoft's not-free client software. When the client operating system goes "live," per Microsoft's strategy, it blurs the practical boundary between those functions the client performs from local resources and those it relies on the service fabric to accomplish.