A record-setting quarter for Apple's iPad led to a better-than-anticipated second quarter for the tablet market, according to preliminary data from IDC.

IDC estimates that total worldwide tablet shipments for the second quarter of 2012 (2Q12) are at 25 million units; up from 18.7 in the first quarter of 2012. That represents a quarter-over-quarter increase of 33.6% and a robust year-over-year growth rate of 66.2%, up from 15 million units in the second quarter of 2011.

"Apple built upon its strong March iPad launch and ended the quarter with its best-ever shipment total for the iPad, outrunning even the impressive shipment record it set in the fourth quarter of last year," said Tom Mainelli, research director, Mobile Connected Devices. "The vast majority of consumers continue to favor the iPad over competitors, and Apple is seeing increasingly strong interest in the device from vertical markets?especially education. While iPad shipment totals are beginning to slow a bit in mature markets where the device saw early traction, growth in other regions is clearly more than making up the difference."

Apple shipped 17 million iPads during the quarter, up from 11.8 million units in 1Q12 and well above its previous record of 15.4 million in 4Q11. Apple wasn't the only company to experience solid growth in the second quarter. Four of the top five worldwide vendors saw their shipments increase year over year. Samsung experienced exceptional growth, and landed in second place with 2.4 million units shipped, up from 1.1 million units a year ago. Amazon rebounded from a sluggish first quarter to post shipments of 1.2 million units (the company, which ships its Fire tablet only in the U.S., entered the market in 4Q11). ASUS shipped 855,454 units, well above its total of 397,048 units a year ago. Finally, only fifth-placed Acer saw its year-over-year numbers decline, as it shipped 385,458 units this quarter, down from 629,222 units a year ago. It's worth noting that shipments of the well-received Google/ASUS co-branded Nexus 7 aren't reflected in these totals, as that product officially began shipping into the channel in the third quarter of 2012.

IDC expects competition in the tablet space to continue to heat up in the second half of 2012. "In addition to major new products from Amazon and quite likely Apple, we can also expect an influx of Microsoft Windows 8 and Windows RT-based tablets starting in late October," said Bob O'Donnell, program vice president, Clients and Displays. "If anything, there's a real risk that people will have too many options from which to choose this holiday season. Consumers baffled by the differences between Amazon and Google versions of Android, or Windows 8 and Windows RT, may well default to market leader Apple. Or they may simply choose to remain on the sideline for another cycle."