Yep, this one will probably go on some historical timeline in a tech museum someday. Less than a year after taking on Microsoft in the Internet browser market, Google tonight announced that it will be going head-to-head with the Redmond company in a market with a much bigger impact on its bottom line: the PC operating system business.

It will be called the Google Chrome OS, sharing a brand name with the company's browser. "It's our attempt to re-think what operating systems should be," write Google executives in a blog post.

"Google Chrome OS is an open source, lightweight operating system that will initially be targeted at netbooks. Later this year we will open-source its code, and netbooks running Google Chrome OS will be available for consumers in the second half of 2010. Because we're already talking to partners about the project, and we'll soon be working with the open source community, we wanted to share our vision now so everyone understands what we are trying to achieve.

"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 user interface is minimal to stay out of your way, and most of the user experience takes place on the web. And as we did for the Google Chrome browser, we are going back to the basics and completely redesigning the underlying security architecture of the OS so that users don't have to deal with viruses, malware and security updates. It should just work."

Maybe now Microsoft executives will finally be able to abandon the notion that IBM is their biggest competitor. The move puts Google in direct competition with Windows on PCs, a product responsible for more than half Microsoft's $22 billion in fiscal 2008 operating profits.

The timing is also fascinating. Microsoft is widely expected to announced next week that Windows 7 is officially done, or "released to manufacturing," to use the lingo. If Microsoft were writing the script, that moment would mark the beginning of a new era in which Windows 7 would return its flagship product in triumph to the top of the tech world -- or at least not be the embarassement its predecessor was.

Now comes Google, promising a new operating system built for the Internet age, with an architecture consisting simply of "Google Chrome running within a new windowing system on top of a Linux kernel."

The official Google blog post makes no explicit mention of a possible business model, but if Chrome OS were to follow the pattern, it would be offered free, with elements that indirectly support or directly boost the company's advertising-based business.

Computer users "don't want to spend hours configuring their computers to work with every new piece of hardware, or have to worry about constant software updates," says the official post, signed by Sundar Pichai, Google vice president of product management; and Linus Upson, Google engineering director. "And any time our users have a better computing experience, Google benefits as well by having happier users who are more likely to spend time on the Internet."

Google acknowledged in the post that there will be areas of overlap between Chrome OS and its Android operating system, which was originally targeted to mobile phones but has since been expanded to run on netbooks. In those cases, the company said, "choice will drive innovation for the benefit of everyone, including Google."

Microsoft hasn't yet issued an official comment on the news.

The New York Times and Ars Technica broke the story prior to the blog post. The Times reports that Google had planned to announce the news Wednesday before receiving inquiries from the paper.

Follow-up: Google: Chrome OS to be free, with major PC vendors on board