SAN FRANCISCO – It’s taking longer than Google Inc. (Nasdaq: GOOG) anticipated to deliver a new operating system designed to make computers run faster.

After more than a year building a much-anticipated system around its Chrome Web browser, Google announced Tuesday that the first laptops powered by the new software won’t hit the stores until the middle of next year. The revised timetable is about six months behind Google’s goal of having the Chrome OS completed in time for it to debut during the current holiday season.

(Read more about Chrome OS, including beta program sign-up, here.)

(Read more about the Chrome browser here.)

Google’s engineers decided they needed more time to fix bugs and fine tune the Chrome OS before the company launches its ambitious challenge to computers running on long-established operating systems made by larger rivals, Microsoft Corp. and Apple Inc.

While Google polishes the Chrome OS, it will collect user feedback through a pilot program allowing a relatively small number of consumers and businesses to test unbranded devices running the software. Consumers will be invited to receive the test laptops through the Chrome Web browser and Google’s YouTube video site. The companies getting the Chrome OS machines include AMR Corp.’s American Airlines, Kraft Foods Inc. Logitech International, and Virgin Airlines.

Acer Inc. and Samsung Electronics Co. will make the first Chrome OS laptops available in stores next year. The prices of the machines will be determined by the manufacturers next year.

The postponement threatens to intensify the competitive challenges facing the Chrome OS machines. More people already are snapping up sleek, touch-screen tablets such as Apple Inc.’s iPad to surf the Web and run a variety of applications customized for the devices. Apple sold about 7.5 million iPads in the first six months after its April debut and the tablet is expected to be among the top-selling gadgets this holiday season.

The rising popularity of the iPad and an array of copycats has started to undercut sales of lightweight laptops, or “netbooks,” according to industry analysts. Even the next version of Google’s Android operating system for touch-screen devices is supposed to include more features tailored for tablets.

The Chrome OS computers will have a 12.1 inch display screen and standard-sized keyboard, but no hard drive. That means the Chrome OS computers will need online access to run more programs. Google is teaming up with Verizon Communications to sell Internet access over Verizon’s wireless network when there is no other way to connect to the Web. Online consumption of up to 100 megabytes per month will be offered for free during the first two years of computer ownership. Larger data plans will cost as little as $9.99 per month with no long-term commitment required.

Google decided to build its own computer operating system primarily because its views the hundreds of millions of machines powered by Microsoft’s dominant Windows software as plodding, cumbersome relics unable to provide speedy Web surfing. The Chrome OS machines are being designed so they’re ready to navigate the Internet within a few seconds after hitting the power button, almost as quickly as a television set is ready for channel surfing .

Developing a Web-based alternative to Windows also realizes a long-held goal of Google CEO Eric Schmidt, who had previously clashed with Microsoft as an executive at Sun Microsystems and Novell Inc. during the 1990s. Google’s development of the Chrome OS contributed to Schmidt’s resignation from Apple’s board in 2009. Schmidt stepped down because he increasingly was steering Google into the same markets as Apple, raising potential conflicts of interest.

By making it easier and more appealing for people to spend time online, Google hopes to attract more traffic to its dominant Internet search engine and boost its revenue by selling more of the ads that generate most of its income.

The push for a speedier Web experience, prompted Google to introduce the Chrome browser more than two years ago. Although it still lags behind Microsoft’s Internet Explorer and the Mozilla Foundation’s Firefox, Chrome has steadily been winning converts. Google says Chrome now has 120 million active users worldwide today, up from about 30 million at the beginning of the year.

Chrome will soon get even faster by pulling up websites as people type in an address, in the same manner that Google’s search engine displays different results with each keystroke. For example, typing “e:” in Chrome’s navigation bar display ESPN’s site in the browser, if that is a destination that the user frequently visits.

To help whet consumers’ appetite for the new Chrome OS machines, Google unveiled a new store that will distribute Web applications that offer more features and better graphics than the content found on standard Web pages. The Web apps store opened Monday with about 500 free and for-fee applications, meeting the end-of-the-year deadline Google established when it announced the idea in May. More than 40,000 applications already have been developed specifically for the iPad.

The New York Times Co., Time Warner Inc.’s Sports Illustrated magazine and video game maker Electronic Arts Inc. are among the major companies already offering applications in the Chrome store. Internet retailer Inc. also previewed an application that for the first time will allow other merchants to sell electronic books for its Kindle reader. The app enables Kindle books to be read through a Web browser.

Like programs designed for the iPad and mobile phones, the Chrome applications store could help publishers bring in more revenue from subscriptions and advertising..

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