Click ‘n’ run. It seems like such a simple concept. Surf up to a Web page, select the desired application from a list, and click. Voila! Microsoft Word appears on your desktop. Or Excel, or Adobe Photoshop… you name it.

[ Symantec SVS won an InfoWorld Technology of the Year award. See the slideshow to view all winners in the platforms category. ]

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In practice, click ‘n’ run is a nightmare to implement. Setting aside the licensing issues (and they are legion), the fact remains that delivering traditional fat client applications over the Internet is a technological hurdle on the scale of enabling pigs to fly. First, you have to package the code in a way that allows it to run without actually installing anything. That’s where virtualization comes in. Then you need to find a way to deliver the bits to the end-user without choking their network connection or leaving them helpless when they no longer have access to the distribution point. Here streaming and caching are the keys.

Previous attempts at Web-based application distribution have focused mostly on kiosk-style computing, using a virtual machine or terminal session running on a back-end server to deliver a “screen-scraped” UI to the remote user. However, with the emergence of application virtualization solutions from Softricity (now part of Microsoft), Altiris (now part of Symantec), and Thinstall, the industry is poised for an explosion of new and potentially revolutionary delivery models.

These three solutions virtualize the interaction between Windows programs and the Windows OS resources they depend on, including the file system and system registry, allowing them to run in isolation from the underlying desktop. (For the differences in how they go about it, see my writeup on application and desktop virtualization in "Virtualization: Under the hood.") Combine the virtualization capabilities with streaming servers, as two of the vendors have done, and click 'n' run, on-demand application deployment is just a step or two away. 

What makes application virtualization so compelling is its immunity to the very issues that torpedoed the kiosk solutions. For starters, virtualized applications are modular. Though streamed by default, virtualized applications can be configured for offline use, either through caching or by simply copying the application image to the client. And though isolated from the local system (because the application’s registry access and private file set are virtualized), they can still interact with local resources, seamlessly accessing the PC’s storage and print devices, for instance.

But despite having the right general plumbing, none of these first-generation solutions is designed specifically with a subscription-based computing model in mind. Microsoft SoftGrid and Thinstall Virtualization Suite are still aimed at internal enterprise deployment, whereas Symantec SVS Pro -- by virtue of its integration with a streaming server component from partner AppStream -- is closer to the goal of a true click ‘n’ run format. All Symantec needs to do is work out the optimization kinks.

It’s worth noting that, although the focus of SoftGrid is still internal, the 800-pound gorilla in Redmond has everything it needs to deliver a future Office suite via the Web. The future of software distribution is subscription-based click ‘n’ run; the question is no longer if, but when. The three platforms reviewed here are helping pioneer the transition.