By  CLAIRE CAIN MILLER
Published: September 8, 2010

SAN FRANCISCO — Google, which can already feel like an appendage to our brains, is now predicting what people are thinking before they even type.

On Wednesday, Google introduced Google Instant, which predicts Internet search queries and shows results as soon as someone begins to type, adjusting the results as each successive letter is typed.

“We want to make Google the third half of your brain,” said Sergey Brin, Google’s co-founder and president of technology, speaking at a Google press event at the San Francisco Museum of Modern Art. Marissa Mayer, Google’s vice president for search products and user experience, added, “There’s even a psychic element to it.”

Google’s new psychic powers result in much faster searches, but the change might affect the many businesses that have been built around placing search ads on Google and helping Web sites figure out how to climb higher in search results to increase revenue.

It is a sign that even as Google expands into other businesses, like display advertising and cellphones, it remains firmly focused on search, its core business and one that accounts for more than 90 percent of its revenue. It has faced competition recently from Microsoft’s Bing search engine.

Google has made its new product the default way to search the Web. Instant works with the most popular modern browsers in the United States and several other countries. It will show up on cellphones and in browser search bars in a few months.

“It’s been awhile since there’s been a game changer in search, and this is,” said Jordan Rohan, an Internet analyst at Stifel Nicolaus. “It changes how people search.” He added that it was a feat of computing and engineering that could not “easily be mimicked by Google’s competition.”

Google’s attempt to greatly change the way people search could throw a wrench in the business models of the companies that have latched onto the Google ecosystem.

Analysts said that it was too early to tell how Google Instant would affect search engine marketing and optimization businesses. But because Web pages and ads show up before people finish typing queries, it could be more challenging and expensive for them to pick keywords that catapult their sites to the top results, analysts said.

For example, it has been less expensive for a small hotel in Paris to buy ads that show up when someone searches “Paris boutique hotels in the Marais” than when someone searches “Paris hotels.” But now that Google immediately starts showing results, people may type long queries less often. As a result, advertisers would have to bid for more common terms.

Also, because Google Instant focuses attention on the search box and top results, people could spend less time looking at the ads that show up on the right side of the page.

“The general murmur is that advertisers are not particularly pleased because they see it as Google strong-arming people to buy the most expensive terms and make the most money for Google,” said Matt Hessler, account director for Trada, a search marketing firm.

Johanna Wright, director of product management at Google, said that Google was not changing the way it ranked or served ads, and that the instant results were more useful for consumers because “we’re getting you your answer much quicker and you’re not having to scroll and wade through information.”

Before the change, Google’s search results probably did not strike anyone as slow. But with Google Instant, they can easily be twice as fast.

Most people’s lives will not change with an extra few milliseconds, but Google calculated that the new tool would cumulatively save people more than 3.5 billion seconds every day, which works out to about 11 hours a second.

The results will also be more useful because people can adjust their searches on the fly, based on what they see, and explore similar queries they might not otherwise have seen, says Ben Gomes, a Google engineer working on search. “We want to give you feedback as you type your query, so you can formulate a better query,” he said.

Still, some users said they found it distracting to see other queries pop up as they were typing. And since Google says that a fifth of searches are brand new, it will not always be able to make an accurate prediction.

“It’s not quite psychic, but it is very clever,” said Othar Hansson, a senior staff software engineer who helped develop Instant.

To make the predictions, Google relies on search trends, like words that are often searched, were recently popular or were searched nearby, Ms. Mayer said.

Some words, like “nude,” produce no results because Google Instant filters for violence, hate and pornography, the company said.

Google, which already handles more than a billion searches a day and has a billion users a week, had to figure out how to manage the load when suddenly each letter typed was a separate search query. The solution includes storing frequent searches and sending common ones, like “Barack,” back more quickly than ones that are nearly impossible to predict, like “Bill.”

“We had to figure out how to do it without melting down our data centers,” Mr. Gomes said.

(Source: A version of this article appeared in print on September 9, 2010, on page B1 of the New York edition.)