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Applications: Clients virtualize beyond recognition

Nov 28, 20054 mins
Development ApproachesEnterprise Applications

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.

But let’s not give Microsoft all the credit for the trend toward client virtualization. Enriched browsers of all varieties – including Macromedia Flash and other vendors’ plug-ins – are blurring the practical distinction between clients and servers even further. Enriched browsers such as those supporting Asynchronous JavaScript + XML (AJAX) deliver a more GUI-like user experience than a basic browser. AJAX-capable browsers, such as Internet Explorer and Firefox, shift the presentation emphasis away from downloading individual Web pages toward navigating within richer, structured, client-side content caches. The enriched browser can execute more application logic, cache more content and perform more rendering locally than a basic browser. And it offloads some or all of these functions from portals, Web sites and other presentation servers.

The offloading can go both ways, of course: Most of the processing power of PCs can be centralized into server chassis, per the network PC approach first introduced in the late 1990s. A new twist on that approach – the blade PC – is the most important development in desktop management in many years. Blades from pioneers HP, ClearCube and IBM virtualize desktop resources into manageable slices of a server’s centralized resources, transforming the innards of each PC into a blade that can be installed in a server chassis. The user relies on a thin-client windowing protocol such as Citrix’s Independent Computing Architecture to interface remotely to what is, essentially, a full-featured dedicated PC.

Clearly, virtualization is transforming client-side computing beyond all recognition. The presentation tier is blurring into the application-server, middleware and networking infrastructures.