With just two quarters of Surface sales under its belt, Microsoft is already one of the top five tablet makers in the world, a report from IDC claims. And the firm sold an estimated 900,000 Surface RT and Surface Pro tablets in Q1 2013, despite limited availability of the latter.

“Many of those units were Surface Pro, which the company started shipping to the United States and Canada in February,” IDC noted. “Microsoft has said that it is actively widening its regional distribution of both Surface RT and Surface Pro products.”

Sales of non-Surface Windows 8/Windows RT tablets didn’t fare so well, IDC said: Total combined shipments across all vendors reached 1.8 million units. This suggests that Microsoft now controls 50 percent of all Windows tablet shipments.

Related: "Microsoft Cracks the Top 5 in IDC's Latest Tablet Report"

Of course, Windows and Surface still have a ways to go to catch up to the market leaders. For the first time, Apple’s dominant iPad grew much slower than the rest of the market and fell to under 40 percent market share, with 19.5 million units shipped in the quarter. In second place, Samsung shipped 8.8 million tablets with an astronomical 283 percent growth year-over-year. ASUS (Nexus 7) and Amazon (Kindle Fire HD) came in third and fourth place, respectively, with 350 percent and 157 percent growth. Overall tablet sales growth in the quarter was 142 percent.

Source: IDC Worldwide Tablet Tracker, May 1, 2013.

Microsoft and other Windows tablet makers are prepping smaller 7" and 8" tablets to try and make up the slack, but IDC suggests these mini tablets might not be the panacea some expect.

“Clearly the market is moving toward smart 7"-8" devices, but Microsoft's larger challenges center around consumer messaging and lower cost competition,” IDC Program Manager Ryan Reith claims. “If these challenges are addressed, along with the desired screen size variations, then we could see Microsoft make even further headway in 2013 and beyond.”

Related: "Tablet Growth Tied to Success of Mini Devices"