Google Inc.'s bid to compete with Microsoft Corp's Windows operating system may help lower the cost of personal computers at a time when prices are already being pinched by inexpensive netbooks.

Google said it will offer its just-announced Chrome operating system for free when it is launched in the second half of 2010, a move that could force Microsoft into a price war.

Although Windows is the dominant operating system - installed on 90 per cent of the world's PCs, Microsoft won't take Google's challenge lightly, analysts said. Its new Windows 7 operating system will be available in October.

Google said Chrome OS, which is based on the open-source Linux code, is being designed for all PCs but will debut on netbooks. It makes sense for Google to initially target the stripped-down, web-centric netbooks, one of the only segments showing any growth in a PC market that is contracting.

Netbooks generally sell for $300 to $400, but prices are dropping as new offerings flood the market and wireless carriers offer subsidies with the purchase of a data plan.

Kaufman Bros. analyst Shaw Wu noted that while the prices on nearly all PC components have been falling, "the one thing that has not been coming down is the cost of the operating system. This is going to put some pressure on Microsoft."

Microsoft doesn't say how much it charges PC brands for Windows, but analysts estimate it gets $20 to $40 for the older XP system used in the vast majority of netbooks, and at least $150 for the current Vista system. Mr Wu said price competition could ultimately give a bump to PC makers' margins.