Updated from 1:38 a.m. EDTGoogle ( GOOG) has upped the ante. The search giant is developing its own operating system in a direct challenge to Microsoft's ( MSFT) dominance of the personal computer market. In a post on its company blog late Tuesday, Google said the Google Chrome OS, an extension of it Chrome Web browser, is an open source, lightweight operating system that initially will be targeted at netbooks. The company said later this year it will open-source its code and netbooks running the operating system will be available for consumers in the second half of 2010. Google said it has begun talking to partners about the new operating system. The blog post was authored by Sundar Pichai, vice president of product management, and Linus Upson, engineering director. "Speed, simplicity and security are the key aspects of Google Chrome OS. We're designing the OS to be fast and lightweight, to start up and get you onto the Web in a few seconds," the blog post said. The Google Chrome OS is separate from Android, the company's operating system for mobile devices. While "Android was designed from the beginning to work across a variety of devices from phones to set-top boxes to netbooks," Google said, the Chrome OS "is being created for people who spend most of their time on the Web, and is being designed to power computers ranging from small netbooks to full-size desktop systems." Google's CEO Eric Schmidt and one of its co-founders, Sergey Brin, are expected to discuss Google's new operating system later this week when they appear at a media conference hosted by Allen & Co. at the Sun Valley resort in Idaho, the Associated Press reports.