Microsoft's decision to extend availability of its Windows XP Home OS for ULPCs (ultra-low-cost PCs) gives developers a chance to bring applications to a broader set of Windows systems, a Microsoft official said Thursday.

These PCs, priced at approximately $400 and built by companies like Asus Systems, represent an emerging class of mobile personal computers, Microsoft said. Windows XP Home, for consumer use, will be available until the later of either June 30, 2010 or one year after the general availability of the next version of Windows, which has been referred to as Windows 7. Plans had called for discontinuing the sale of XP after June 30.

"It's going to mean more Windows customers [for software developers] than they ever had before," said Kevin Kutz, Microsoft director for Windows clients. Microsoft announced the extension on Thursday.

"There are going to be people who get to participate in the Windows experience through ULCPC who might otherwise have not had the opportunity," he said.

Microsoft's new Silverlight graphical presentation technology could run on Windows XP Home in some form, Kutz. Graphical limitations for Silverlight would be driven more by the hardware, he said.

"We're seeing overwhelming demand for Windows on these devices," Kutz said. Asked if the move was in response to usage of the rival Linux platform on the desktop as a competitor to Windows, Katz said Microsoft sees growth in this category of PCs and that partners and customers want Windows on these devices, Kutz said.

Asked why these users could not just use the latest Windows desktop, Windows Vista, Kutz cited hardware issues, such as screen size and processors. "[There are] hardware constraints that make Windows XP Home a more effective choice on the basis of performance and cost," Kutz said.

Citing a reluctance by businesses to move to Vista, InfoWorld has launched a campaign to save Windows XP. But Kutz stressed technical support for XP will be offered through April 2014. Outside of the Home edition, sales of XP via retailers ends June 30. System builders can sell XP until January 31, 2009.