Google, the California-based search engine company, last night unveiled a product that will allow computer users to locate files on their hard drive as easily as they can find pages on the web with one of its searches.

It marks the recently floated company's latest challenge to the dominance of software giant Microsoft.

Analysts predict that Google Desktop may be the latest stage in the development of a suite of powerful web-based applications from Google that could challenge Microsoft's dominant Windows operating platform.

In April, Google announced it was launching its own web-based e-mail service, Gmail, offering users one gigabit of space, or 500 times more than Microsoft's free Hotmail service.

The Gmail service, paid for by ads that relate to the content of the e-mails, added various functions unavailable to Hotmail users, including the chance to call up the entire "thread" of an e-mail exchange.

Google has also registered the domain name Gbrowser.com and has recruited some of the programmers who worked on Microsoft's Internet Explorer web browser, leading to speculation that the company was also working on its own browser.

Such a browser would make it easier for Google to introduce other applications - for example, word processing or business accounting - to threaten Microsoft's core market.

Immediately, the new Google Desktop only actually works on the Windows platform, sitting on the Google toolbar or web page giving users the chance to search for Microsoft Outlook messages, Word, Powerpoint, or Excel files, AOL Instant Messenger files, and any HTML page saved to the hard drive or viewed through Internet Explorer.

Easy to download, it starts to catalogue the contents of a PC's hard drive as soon as the computer is inactive. "We think of this as the photographic memory of your computer," Marissa Meyer, the head of Google's consumer Web products, said.

But even if Google Desktop, released as a Beta test product, works only with Windows-based PCs for now, analysts say that Microsoft should be getting nervous about Google's longer term strategy.

"It's a real blurring of the divide between the information that's on your desktop and the information that's on the internet," Joe Wilcox, an analyst with Jupiter Research, said. "That's a dramatic change in how people view the PC."

Danny Sullivan, a search engine expert, agreed. "They've not only beat their rivals to the punch, they've also changed the rules," he told tech news service CNET. "They're saying, 'We're not making search part of the operating system, we're making the desktop part of Google'."

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