Apple on Wednesday launched the iPad, which it termed "a revolutionary device for browsing the web, reading and sending email, enjoying photos, watching videos, playing games, reading e-books, and much more."

The tablet computer, which is viewed as a big brother to the iPhone, includes 12 new apps designed especially for iPad and almost all of the 140,000 apps available on Apple's App Store. At just 0.5 inches thick and 1.5 pounds, iPad is thinner and lighter than any laptop or notebook. iPad will be available in the US March at a starting price of $499.  It will be launched internationally in June or July.

With its larger size, the iPad's virtual keyboard comes a step closer than the iPhone's to replicating a real keyboard, with "keys" people can touch with two hands and all of their fingers.

The iPad is designed to run just one application on the screen at time and doesn't allow multitasking. It also lacks a built-in camera to take photos and video and the ability to play Flash-based content on web sites.

Apple has opened its first electronic book store, and it allows users to download and buy books on the move. Deals have already been agreed with publishers, including Penguin and HarperCollins. Once a user has bought a book, it appears on a virtual bookshelf, complete with cover art, and can then be read on the device in full colour. The iPad uses the open-source ePub format, which means books downloaded will be compatible with other devices.

However, most people buy their books online from retailers like Amazon who have the option of using the Kindle e-reader.

Apple sees its new device as filling the gap between smartphones such as the iPhone and laptop computers, providing the range of services from e-mailing and web browsing to viewing videos and reading e-books.

"If there's going to be a third category it has to be better at these tasks, otherwise it has no reason for being," said Apple co-founder Steve Jobs, at the launch in San Francisco.

Jobs had a liver transplant in early 2009 and was first diagnosed with pancreatic cancer in 2003.

He said Apple's total revenues from mobile products - - including its iPod and iPhone lines - -  now exceeded those of Nokia. "We're a mobile company. That's what we do," he said.

Nokia is currently suing Apple over patent infringements in the iPhone and on Wednesday, Japanese computer maker Fujitsu said it is the owner of the "iPad" trademark.

Van Baker, research vice president at technology research firm Gartner, said: "It's a home run. You can use it in classrooms, the living room, or anywhere else."

In a report on Wednesday, research firm IDC said the iPad constitutes a new type of gaming device because it has a powerful processor.

"The iPad (will likely) emerge as a significant device category for casual gamers," IDC said in the report, which estimated Apple would ship 4 million iPads worldwide this year.

Insight on the iPad debut, with the Power Lunch team and CNBC contributor Paul Kedrofsky: