According to a recent study by iSuppli, the iPad so thoroughly owns the tablet market that its nearest competitor isn’t a tablet at all: it’s the iPhone 4S. In the fourth quarter of 2011 Apple shipped 15.4 million iPads. That number was lower than expected for the quarter, but the hit to the iPad’s market share came from the iPhone 4S, which launched at the beginning of the quarter, and which ate up a lot of disposable income that might otherwise have gone toward iPads.

Amazon, meanwhile, had a strong showing with their Kindle Fire tablet, which sold 3.9 million units during the fourth quarter. Unlike the iPad, the Kindle Fire met analysts’ expecations almost exactly. Sales of the Kindle Fire also allowed Amazon to surpass Samsung to take second place in the tablet market for the quarter, after the iPad. Samsung retained second place for the year, however. In both cases, Amazon and Samsung were in second by a huge margin. Apple’s 15.4 million sales in the fourth quarter are almost quadruple Amazon’s Kindle Fire sales, and their 40.5 million sales for the year are nearly seven times Samsung’s sales.

The study also predicted that Apple would make up for its losses in market share in the first half of 2012 with the launch of the iPad 3. The tablet market as a whole continued to grow in 2011. Total tablet sales came to 65.2 million units, beating analysts’ expectations by half a million units.