Microsoft typically holds a Professional Developers Conference (PDC) on the eve of a major platform launch as a way to prep developers for the future. There was the Windows NT introduction in 1992, ActiveX in 1996, .NET in 2000, and Longhorn in 2003. This year's PDC—PDC10—was quite a bit different, however. At the show, Microsoft talked up in-progress platforms such as Windows Azure and Windows Phone. Sure, much of the technology and information discussed at the show was new to some attendees. But none of it was truly new. Not really.

Well, except for one thing. There was one quiet, almost completely overlooked bit of new information at PDC10. And it will have far-reaching ramifications for both developers and the software giant.

After years of touting Silverlight as its cross-platform solution for the web, Microsoft said it was dropping or at least deemphasizing the proprietary technology in favor of the truly open HTML 5 web standard. It will still continue to develop and improve Silverlight, but only in its use as the basis for Windows Phone applications. Silverlight on the web, for all intents and purposes, is dead.

"HTML is the only true cross-platform solution for everything, including \\[Apple's\\] iOS platform," Microsoft President Bob Muglia told ZD Net's Mary Jo Foley. "Silverlight is our development platform for Windows Phone."

Although Microsoft had originally positioned Silverlight as its version of Adobe Flash, and focused largely on high-quality video playback, future versions picked up much of the functionality of the Windows-based Windows Presentation Foundation (WPF) technologies, with Microsoft offering the environment as a way to create professional-looking web applications. Earlier this year, the company announced that Silverlight would be the environment for Windows Phone applications, as well.

With Microsoft embracing hardware-accelerated HTML 5 and related technologies in its upcoming Internet Explorer (IE) 9 web browser, however, the strategy has changed. Now, the company has a first-class HTML 5 solution, one that integrates web apps with Windows. Indeed, Microsoft is so serious about HTML 5 that it just added more developer features to IE 9, well after a feature-complete beta release that was supposed to represent the shipping version of the browser.

This shift also makes previously released documents about Windows 8—the next Windows version for PCs—appear more probable. Those documents, described in my article Windows 8: A First Peek, noted that "Microsoft is investigating HTML 5 and JavaScript as an alternative \\[for Windows 8 application development\\], providing tiers of programming models that would be accessible to all kinds of developers ... integration with the web will enable a My Applications scenario where applications and application settings follow users from device to device."

Developers can expect an update on Silverlight by MIX'11, a web developer conference that Microsoft will hold in April 2011. But in the meantime, those interested in targeting the web should be looking at HTML 5, not Silverlight. That's what Microsoft is doing.