The PDC (Professional Developers Conference) is ground zero for Microsoft's big new ideas. This year's event, which kicks off today, promises to be the most momentous since 2003, when Microsoft began talking up the technologies underlying Longhorn — which eventually spawned Vista, Windows Server 2008, and a bunch of important web services protocols. The failure of Vista, which Microsoft still stubbornly refuses to acknowledge, raises the stakes for this year's PDC. All eyes will be on Windows 7, which will be revealed behind closed doors to select few. But as InfoWorld's Randall C Kennedy has been saying since June, no one should expect Windows 7 to be a major departure from Vista — it will be more like Vista Second Edition, with similar system requirements. Big surprises seem unlikely. So what's the main event? The unveiling of Microsoft's so-called cloud OS and the development tools and models for it. [ Steve Ballmer said at a recent London conference that a new "Windows Cloud" operating system will be unveiled at PDC ] For years Microsoft has struggled to clarify its cloud strategy: On the one hand, to compete with Google, it realises it must embrace a new world of cloud-based apps and services; on the other, it's terrified of cannibalising its desktop software business. The vague Microsoft answer to this conundrum has been "software plus services", where locally installed Microsoft software integrates with services or apps in the cloud. For that idea to work, however, you need a platform on which to build and run those cloud services and apps, and that's exactly what Microsoft is poised to reveal. Earlier this month, Microsoft's director of the platform strategy group, Tim O'Brien, told me that PDC will "round out the picture at the OS and developer infrastructure level" for those who want to "participate in the transformation to services". In other words, developers are going to find out what Microsoft's new cloud platform really is and how to build on it. Various code names for the layers of Microsoft's cloud have floated around, such as Red Dog (infrastructure?) and Zurich (runtime environment?), as well as several theories about the platform's structure. And a casual look at the PDC schedule provides some strong hints. Cloud sessions abound, from building a first cloud service to extending local .Net services into the cloud. And we already know pretty much about Microsoft's Live Mesh, which is both a development platform and a folder-sharing and synchronizing service for end-users. For me, what's really exciting about all this is that when you throw in the forthcoming .Net 4.0 Framework and the new Oslo modelling language, you have all the elements necessary for creating and orchestrating services into composite applications that may include services in the cloud. That's a software-plus-services strategy that makes sense to me. Over the long haul, it might even breathe new life into service-oriented architecture. But I'm getting ahead of myself. As usual, it's all in the execution, and if the past is any guide, we won't be able to evaluate how well Microsoft has done until months after PDC is over.