Google's Desktop Search application, released today, sorts through desktop files of all sorts, as well as AOL Instant Messenger chats and Web sites the user has visited.

"We saw that users couldn't remember where they saw information. We decided the paradigm shouldn't be, 'what's stored on your computer,' but rather 'what have you seen?'" said Marissa Mayer, Google's director of consumer Web products.

The downloadable tool indexes content created by the desktop computer or accessed by the browser whenever the computer is idle for 30 seconds or longer. The advantage, Mayer said, is that files are available for search soon after they're created.

She said even Web users who spend a lot of time online shouldn't fill up their disk space, however. "We're using some of the most advanced compression we can find, and disk utilization never gets above 2 gigabytes," she said. The lightweight application itself requires 400 kilobytes of memory, making it half the size of the Google toolbar. It uses 8 megabytes of memory.

Users can access desktop search via an icon installed in the Windows taskbar or at Google.com. Desktop search via the taskbar can be accomplished without an Internet connection.

"We host the user interface in HTML, and it runs on your local computer. We're running a small Web server on your machine," Mayer said. The idea was to make the desktop search experience as much like Web search as possible.

Google Desktop Search works with Windows XP and Windows 2000 Service Pack 3 and above. It requires 500MB of available hard disk space, a minimum of 128MB of RAM and a 400MHz or faster Pentium processor. Mayer said the product aimed at the middle of the road; based on various industry data, Google estimates that only about 10 percent of Windows users won't be able to use the product.

Mayer said that a direct business model for Google Desktop Search wasn't apparent. "Google tends to release products that focus first on user needs and user experience and see if it delivers utility," she said. "If a product is high-utility, you'll find a business model easily." She pointed out that Google launched its now highly profitable Web search without a way to monetize it, then developed its AdWords advertising product.

But she said the company is betting that most users will access Desktop Search from Google.com or the Google toolbar on the browser, rather than via the taskbar. In fact, she said Google will train them to do this, because even when users go to Google.com and search the Web, the desktop client also searches the desktop. Then, when the page of Web results is delivered, it includes a note at the top that more results are stored on the computer.

"We believe that most people would like to search both the desktop and the Web at the same time," Mayer said. "If that's true, most people will access the functionality from the Google home page or task bar. So, people who used to do 30 searches a week will now do 40. If they're done on core Google search, they'll be monetized [via ads]."

Danny Sullivan, editor of Search Engine Watch, said that, while he always thought people would differentiate between Web and desktop search, the way Google provides the two has made him change his mind. "I think people will just think of going to Google to do a search," he said. While they may use the toolbar or the taskbar icon, he said, "The important thing is, this will further point them in Google's way." (Search Engine Watch and internetnews.com are both owned by Jupitermedia.)

Mayer said the convergence of Web and desktop search is fueled by the blurring of the distinction between the Web and the local computer. "People don't remember where they saw something, or in what format it was," she said. "All they remember is that they saw it. That's why Google Desktop Search strives to be a photographic memory for your computer. If it showed up on your screen, you should be able to find it."

Sullivan said the product is aimed squarely at non-technies like his mom. "This is ideal for her, not just to help with Web searching but to find things all over her computer. My mother doesn't know her file structure or where she stores her data."

Sullivan thought the most powerful part of the application was the ability to search one's Web history, a feature that rivals Ask Jeeves, Yahoo and Amazon's A9 search service provide. However, Google's is on by default, as is A9'S; Ask Jeeves and Yahoo users must turn it on. "Ideally, it should be designed so that it's easy for you not to use it if you don't want it. They may have to go further into letting you switch these things off," Sullivan said.

One big plus for Google's history feature is that, unlike its rivals' services, the information is stored on the computer's hard drive, rather than on the search provider's Web servers.

"Your Web history is already stored on your computer by default, so it's not so much of a jump," he said. But the ability to search the whole desktop and Web history from a single application makes local privacy trickier. While an office mate or manager can already look at the browser cache to see what sites someone had visited, Google Desktop Search makes it fast and easy to search the whole machine.

"For first time," Sullivan said, "somebody could run over to your computer and, in a few seconds, find out whether you were up to something."