The worldwide market for tablet computers is expected to climb almost fourfold in 2011 according to a recent report from Gartner.

The research firm estimates 70 million tablets will be sold this year, up from 17.6 million in 2010. The firm also predicts sales of 294 million by 2015.

Despite mounting competition from other operating systems (OSs), Gartner predicts Apple’s iOS will continue to own the majority of the worldwide media tablet through 2015. Gartner believes iOS will account for 69 percent of media tablet OSs in 2011, and represent 47 percent of the media tablet market in 2015.

Gartner analysts believe the iPad has re-invented the tablet PC market in the same manner the iPhone re-invented the smartphone market. Gartner's prediction for iOS' market share remains strong because it believes Apple's edge is its rich ecosystem of applications rather than more feature laden hardware

“Seeing the response from both consumers and enterprises to the iPad, many vendors are trying to compete by first delivering on hardware and then trying to leverage the platform ecosystem,” said Carolina Milanesi, research vice president at Gartner. “Many, however, are making the same mistake that was made in the first response wave to the iPhone, as they are prioritizing hardware features over applications, services and overall user experience. Tablets will be much more dependent on the latter than smartphones have been, and the sooner vendors realize that the better chance they have to compete head-to-head with Apple.”

Google’s Android OS is forecast to increase its worldwide share of the media tablet market from 20 percent in 2011 to 39 percent in 2015. Analysts said Google’s decision not to open up the Honeycomb, its first OS version dedicated to tablets, to third parties will prevent fragmentation, but it will also slow the price decline and ultimately cap market share.

Tablets running Research in Motion's QNX operating system are expected to capture 5.6 percent of the market in 2011, rising to 10 percent in 2015. (see chart below for Gartner’s complete predictions)

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