The world's top high-tech fair opens Tuesday with the IT industry in bullish mood, preparing to wow visitors with head-spinning futuristic gadgets and the latest in 'cloud computing' technology.

More than 4,200 tech firms from 70 countries are expected to attend this year's CeBIT -- the self-styled "Davos of high-tech" -- with many of the big names that stayed away during the global financial crisis returning to Germany.

Google, IBM, SAP, Microsoft, HP and Dell are among the top companies setting up their stalls in Hanover, northern Germany, for the five-day event that is likely to attract around 350,000 punters and self-confessed technology geeks.

"CeBIT 2011 is the heart of the digital world and will show how rapidly the pulse of the IT industry is beating," said Ernst Raue, board member of Deutsche Messe that organises the event.

As the event approached, BITKOM, which represents Germany's telecom and high-tech sector, forecast a 4.8-percent gain in the global IT market to 2.6 trillion euros ($3.6 trillion) this year, driven by double-digit growth in China.

Despite the optimism, however, the CeBIT fair is not the global showcase it once was. Exhibitor numbers are up only fractionally on last year and at the height of the dot.com boom, more than 8,000 firms set up shop at the show.

The major theme of this year's fair is cloud computing which "runs like a leitmotiv through the different exhibitions," according to BITKOM president August-Wilhelm Scheer.

Firms will be hoping to move cloud computing -- the idea of storing data online rather than physically on users' machines -- from the realms of the IT world into consumers' everyday lives, said Scheer.

"Cloud computing is going to change IT and its business model enormously. We expect cloud computing sales in Germany to quadruple by 2015," he said.

Other hot topics at the exhibition will be web security, high-speed Internet and bringing 3D computing into everyday life.

But as ever at the CeBIT, it won't be all work and no play.

Firms will be bringing with them a huge range of eye-popping futuristic gadgets to amuse visitors.

The latest robots will be on show, from one that plays table tennis to a "RoboThespian" that recites Shakespeare, to a metal colleague that stands in for you in meetings, showing your face on its monitor.

This year's CeBIT will also have a special section on sports and technology, featuring an "intelligent sensor suit," a full body tracksuit that monitors athletes' movements and enables them to improve training routines.

And there will be no lack of quirky gadgets, from the relentless alarm clock that won't stop until its pressure sensor knows for sure you are out of bed to remote control devices that can be operated using just the power of thought.

Also during the fair, top computer gamers from Europe, Asia and the United States will face off for the title of world video game champion 2011, with a prize of 130,000 dollars at stake.

The show will be officially launched on Monday evening by Chancellor Angela Merkel and Turkish Prime Minister Recep Tayyip Erdogan who will also hold political talks afterwards likely to focus on Turkey's EU accession bid.

On Tuesday, when the fair opens to the wider public, Merkel and Erdogan will take a traditional turn around the grounds to view the stalls.

Turkey, this year's "partner country," is bringing around 100 companies to the show.