UPDATE 5-Google takes aim at Microsoft with new PC platform

* Google to launch free PC operating system in H2 2010

* Move takes direct aim at Microsoft Windows

* New Chrome OS to power PCs, from netbooks to desktops

* Partners include HP, Texas Instruments, Acer, Qualcomm

* Google shares rise 1.5 pct, Microsoft up 0.1 percent (Adds details on pricing, partners, closing share prices)

By Alexei Oreskovic

SUN VALLEY, Idaho, July 7 (Reuters) - Google Inc (GOOG.O) plans to attack Microsoft Corp's (MSFT.O) core business by taking on the software giant's globally dominant Windows operating system for personal computers.

Google, which already offers a suite of e-mail, Web and other software products that compete with Microsoft, said it would launch a new, free operating system that will initially be targeted at netbooks.

Called the Google Chrome Operating System, the new software will be in netbooks for consumers in the second half of 2010, Google said in a blog post, adding that it was working with multiple manufacturers.

Netbooks are low-cost notebook PCs designed for Internet surfing and other Web-based applications.

"It's been part of their culture to go after and remove Microsoft as a major holder of technology, and this is part of their strategy to do it," said Rob Enderle, principal analyst at Enderle Group. "This could be very disruptive. If they can execute, Microsoft is vulnerable to an attack like this, and they know it," he said.

Google and Microsoft have locked horns over the years in a variety of markets, from Internet search to mobile software. It remains to be seen if Google can take market share away from Microsoft on its home turf, with Windows currently installed in more than 90 percent of the world's PCs.

Key to success will be whether Google can lock in partnerships with PC makers, which currently offer Windows on most of their product lines.

Google said in a blog post on Wednesday that it is working with a number of PC makers including Hewlett-Packard (HPQ.N), Acer (2353.TW), Lenovo (0992.HK) and Asustek (2357.TW), as well as chipmakers Texas Instruments (TXN.N) and Qualcomm (QCOM.O) to design and build Chrome devices.

The news comes as executives from the world's biggest technology and media companies, including Google and Microsoft, gather in Sun Valley, Idaho for an annual conference organized by boutique investment bank Allen & Co.

A spokesman for Microsoft declined to comment.