(Reuters) - New Google Inc software will start up a computer as fast as a television can be turned on, the search company said on Thursday as it showed off its Chrome operating system designed for PCs that do their work on the Web

Google gave the first public look at its Chrome OS four months after declaring its intention of developing the PC's main software, a move that pits it directly against Microsoft Corp and Apple Inc.

True to Google's Internet-pedigree, the Chrome OS resembles a Web browser more than it does a traditional computer operating system like Microsoft Windows, matching Google's ambition to drive people to the Web -- where they can see Google ads.

Google said the software will initially be available by the holiday season of 2010 on low-cost netbooks that meet Google's hardware specifications, such as using only memory chips to store data instead of slower hard drives, the current standard.

Netbooks running Chrome OS will only be able to run Web applications and the user's data will automatically be stored on the Web in the so-called cloud of Internet servers, Google executives said at an event at the company's Mountain View, California headquarters on Thursday.

"It's basically a Web browsing machine," said Altimeter Group analyst Charlene Li, referring to the netbooks powered by Chrome OS.

Such a machine is made for a world of near-constant, extremely fast Web connection, without the type of software that made Microsoft famous, since most of the work would be done by big machines on the Web which take directions and send information to relatively uncomplicated devices like a Chrome PC.

Sundar Pichai, vice-president of product management for Google's Chrome OS, said that computers running Chrome OS will be able to start in less than seven seconds.

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"From the time you press boot you want it to be like a TV: You turn it on and you should be on the Web using your applications," Pichai said.

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Google said it is giving away the software for free, similar to its Android smartphone software, with the idea that improving the Web experience will ultimately benefit its Internet search advertising business, which generated roughly $22 billion in revenue in 2008.

"They're doing it to get further and further entrenched in whatever people are doing to go online, whether that's a browser, an operating system or in applications," said Todd Greenwald, an analyst with Signal Hill Group.

"If Chrome is the OS then the attach (access) rate on Google searches will be a lot higher," he said.

But analysts noted that the differences between conventional PCs and Chrome OS netbooks might give some consumers pause.

"If they view it from the conventional perspective, then it falls short," Gartner analyst Ray Valdes said of Chrome OS, citing its lack of compatibility with traditional software and its limited offline capabilities.

Google officials said Chrome OS netbooks will be able to provide some functions when offline, but that the product was primarily designed to be connected to the Internet.

But Valdes said if Google can deliver on the products' promises, such as fast performance, then consumers may view Chrome OS netbooks as distinct class of products with attractive benefits.

"I think that it's initially going to appeal to small subset of the general consumer population," said Valdes. "The question is can they build on that and expand that over time."

Google made the computer code for the Chrome OS available to outside developers on Thursday, allowing developers to tinker with the software and potentially design new applications to run alongside it.

With Chrome, Google is seeking to challenge the dominance of Microsoft Corp's Windows, which runs on nine out of 10 personal computers.

The Chrome OS also challenges makers of traditional, desktop software, including Microsoft and its lucrative Office suite of productivity software, since Chrome OS only runs Web applications.

Google's Pichai, noted during a demonstration on Thursday, that Chrome OS-based PCs would be interoperable with Web-based versions of software, such as Microsoft's online version of its Excel spreadsheet.

Google said all data in Chrome will automatically be housed in the so-called cloud, or on external servers, but also cached on the computer's internal hardware to boost performance.

If a person loses their netbook, Google Engineering Director Matt Papakipos explained, they can buy a new one, log in and within seconds have a machine with access to all the same data as their previous device.

"What really makes this a cloud device is that all the user data is synced back to the cloud in real time," said Papakipos.

Shares of Mountain View, California-based Google fell $3.66 to $572.99 in afternoon trading on the Nasdaq.

(Additional reporting by Ian Sherr)

(Reporting by Alexei Oreskovic, writing by Gabriel Madway; Editing by Bernard Orr and Carol Bishopric)