Microsoft says PC makers are keen to enter the market but want to keep ULPCs as a distinct category from "value" and mainstream PCs. The company's new program, scheduled to launch by the end of June, is designed to help make that happen.

Microsoft plans to charge PC makers US$26 for Windows XP Home Edition for ULPCs sold in emerging markets such as China and India, and $32 for those sold in developed markets, the documents show. PC makers who are eligible for its Market Development Agreement, however, can get a discount of as much as $10 off those prices, the documents say.

That's where the hardware limits come in. Besides limits on the screens and hard drives, to be eligible, the systems can have no more than 1G byte of RAM and a single-core processor running at no more than 1GHz. The program makes an allowance for some chips, including Via Technologies' C7-M processors, which run between 1.0GHz and 1.6GHz, and Intel's upcoming Atom N270.

By offering Windows XP Home Edition at bargain prices, Microsoft hopes to secure its place in the ULPC market and reduce the use of Linux, according to an official at one PC maker, who asked not to be identified because he was not authorized to discuss the program.

"[Low-cost PC makers] have made some good inroads with open-source, and Microsoft wants to put a stop to it," the official said.

The official did not seem opposed to the program. It should stimulate more competition between Windows and Linux in the ULPC market, and it could invigorate sales because consumers who want an easy-to-use PC are likely to prefer Windows, the official said.

Microsoft has said it plans to stop selling new Windows XP licenses after June 30, but it has made exceptions, including for the use of XP Home in ULPCs.