Tablet computers fueled growth in 2012 in the market for "smart connected devices," which crossed the threshold of one billion units for the first time, a study showed Tuesday.

A report by the research firm IDC said worldwide shipments of these devices -- personal computers, tablets and smartphones -- grew 29.1 percent in 2012 to 1.2 billion units with a value of $576.9 billion.

The expansion was largely driven by 78.4 percent growth in tablet shipments, which hit 128 million in 2012.

IDC said sales of desktop and portable personal computers fell 4.1 percent and 3.4 percent, respectively, for the year, while smartphones were up 46 percent.

Looking ahead, IDC forecast tablet shipments will surpass desktop PCs in 2013 and portable PCs in 2014. It predicted tablet sales would grow another 48.7 percent this year to 190 million units.

The smartphone market is expected to grow 27.2 percent to 918.5 million units, IDC said, and sales of traditional PCs will struggle again, especially in emerging economies.

"In emerging markets, consumer spending typically starts with mobile phones and, in many cases, moves to tablets before PCs," said IDC analyst Megha Saini.

"The pressure on the PC market is significantly increasing and we can see longer replacement cycles coming into effect very soon and that, too, will put downward pressure on PC sales."

IDC said Apple closed the gap with market leader Samsung in the fourth quarter, as the combination of Apple's iPhone 5 and iPad Mini brought Apple up to 20.3 percent market share versus 21.2 percent for Samsung for these devices.

But because Apple devices are pricier, the US firm had 30.7 percent of revenues to 20.4 percent for Samsung.

IDC predicts the worldwide smart connected device space will continue to surge with shipments hitting 2.2 billion units and revenues of $814.3 billion in 2017.