San Francisco - Google celebrated its 15th birthday Thursday with a trip down memory lane, and an update to the search engine formula which helped spawn the tech giant.

The company took journalists on a tour of where it all started - Susan Wojcicki's garage in Menlo Park, California, where Larry Page and Sergey Brin began working on Google in 1998. Wojcicki is currently a Google vice president.

A Google+ page meanwhile included a photo album of the original home search page, and collected dozens of birthday wishes.

But Google, which has grown into one of the world's biggest companies, was not content to just look at the past. It announced an upgrade to its main search engine, referred to as 'Hummingbird' with new ways to integrate its use across different devices.

Since 1998, the tech world has changed dramatically and Google said its search engine has been constantly improved.

“The world has changed so much since then: billions of people have come online, the web has grown exponentially, and now you can ask any question on the powerful little device in your pocket,” said Google Search chief Amit Singhal in a blog post.

‘Hummingbird’

Google has quietly retooled the closely guarded formula running its Internet search engine to give better answers to the increasingly complex questions posed by Web surfers.

“It's cleaner and simpler, optimized for touch, with results clustered on cards so you can focus on the answers you're looking for,” said Danny Sullivan of the tech blog Search Engine Land, about the upgrade of the main search engine. "Hummingbird is especially designed to handle complex queries."

The changes could have a major impact on traffic to websites. Hummingbird represents the most dramatic alteration to its search engine since it revised the way it indexes websites three years ago as part of a redesign called ''Caffeine,'' according to Amit Singhal, a company vice president. He estimated that the redesign would affect about 90 percent of the search requests Google gets, thereby changing Any reshuffling of Google's search rankings can have sweeping ramifications because they steer so much of the Internet's traffic.