Apple normally releases a new iPad in the spring, but it has moved to fall launches to take advantage of the lucrative holiday shopping season. That means people who want iPads may be holding out for a new model. Samsung and other rivals have released new tablet models this spring, but IDC says those launches didn't get the spillover boost that a new iPad would have provided.
Mainelli said he expects weakness to continue in the July-September period, but tablet shipments should pick up again in the holiday quarter, when Apple and others are expected to release new products.
Besides a new iPad, Amazon.com Inc. is likely to refresh its Kindle Fire line, while Google Inc. is expected to come out with a new 10-inch Nexus model. Google released a new 7-inch Nexus last week.
Apple remains the leading maker of tablets, with 14.6 million shipped in the April-June period. But as disclosed in the company's earnings report last month, shipments fell 14 percent from a year ago. IDC says Apple's market share fell to 32 percent in the second quarter, compared with 60 percent in the same period in 2012.
Samsung Electronics Co., maker of the Galaxy line of phones and tablets, saw shipments nearly quadruple to 8.1 million in the second quarter. That gave Samsung a market share of 18 percent, up from 7.6 percent a year earlier.
Mainelli said Samsung "is certainly gearing up to be Apple's biggest competitor in tablets, but I think it will still be some time before they catch them."
Meanwhile, makers of Android tablets, in general, are benefiting from the introduction of smaller, cheaper tablets with screen sizes of about 7 inches diagonally. Apple didn't come out with its iPad Mini until the fall. Mainelli said the smaller screens "made it possible to have a decent experience running Android smartphone apps on the tablets. This helped Android overcome the lack of tablet-specific apps in the market."
AsusTek Computer Inc., which makes the Nexus 7 for Google along with its own branded Android tablets, was No. 3 with 2 million tablets. It was followed by Lenovo Group with 1.5 million and Acer Inc. with 1.4 million. Microsoft Corp., maker of the Surface tablets, dropped out of the top five after coming in at No. 5 in the first quarter, according to IDC. Amazon also lost its top-five status. It had been No. 4 in the first quarter.
A look at 5 iPad models since 2010
Apple usually releases a new iPad in the spring, but the company has moved to fall launches. IDC says tablet computer shipments have slowed as a result, though they are expected to pick up again when a new iPad comes out, likely this fall. Here are Apple's iPad releases since the tablet's debut in 2010.
iPad, April 3, 2010. Original model (announced Jan. 27, 2010).
iPad 2, March 11, 2011. Faster processor, thinner. Comes with two cameras for taking photos and video chatting (announced March 2, 2011).
iPad (third generation), March 16, 2012. Faster processor, much sharper screen and improved camera (announced March 7, 2012).
iPad (fourth generation), Nov. 2, 2012. Faster processor, faster Wi-Fi and new Lightning connector, matching what's found in the iPhone 5.
iPad Mini, Nov. 2, 2012. With 7.9-inch screen, instead of 9.7 inches. Screen resolution is 1024 by 768 pixels, same as original iPad and iPad 2.