Global tablet shipments will surge to 350 million units by 2017 as smaller, cheaper devices gain market share and devices powered by Google Inc.'s software gain ground against Apple Inc.'s iPad devices, according to IDC.

Sales of handheld computers will reach 190.9 million units this year, IDC said in a statement today, higher than it's prior prediction for 172.4 million.

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Devices running Google's Android software will command 49 percent of the tablet market this year, higher than IDC's previous prediction for 42 percent.

Apple's share will slip to 46 percent from 51 percent last year, IDC said. Sales of smaller, cheaper alternatives to the iPad, including machines from Inc. and Samsung Electronics Co., are aiding Google's gains on Apple.

"One in every two tablets shipped this quarter was below 8 inches in screen size," Jitesh Ubrani, an analyst at IDC, said in the statement. "We expect smaller tablets to continue growing in 2013 and beyond." Microsoft Corp.'s Windows 8 software will be used on 7.4 percent of tablets by 2017, up from just 1 percent last year, IDC said. Devices with the operating system, including Microsoft's Surface tablet, will take share from both Apple and Google.

As multi-functional tablets gain in popularity, fewer consumers will buy dedicated e-readers from Amazon or Barnes & Noble Inc. After peaking at 26.4 million units in 2011, e-reader shipments slipped to 18.2 million last year and will "grow only modestly" this year and in 2014 before starting a gradual decline by 2015, IDC said.