Gartner believes Windows will recover from its two-year slump, with total device shipments running the operating system climbing by nearly 10% in 2014 and almost 18% in 2015.
For 2013, Windows' share of the operating systems on all "smart devices" - smartphones, tablets, PCs, ultra-light form factors, and PC-tablet hybrids - dropped 5.3% compared to the year before, an additional percentage point from the 4.3% decline the research company predicted in October, and nearly three times the 2% pegged in June.
Gartner's figures for 2013 put the blame for Windows' weaker performance on the continued contraction of the traditional PC business - desktops and notebooks - as well as slower-than-expected shipments of "ultramobiles." That category includes hybrids and two-in-one designs - devices that can convert from tablet into notebook, and back - as well as ultra-light "clamshell"-style laptops.
For 2013, those device groups slumped by 10%, a larger drop than the 8% Gartner forecast a little more than three months ago.
This year will be flat for PCs and ultramobiles, said Gartner, with shipments of approximately 318 million units. The form factors will make a small recovery in 2015, climbing 5% to 332 million.
That figure, however, would still represent a 5% shortfall from 2012, when nearly 351 million such devices shipped.
"Users continue to move away from the traditional PC, as it becomes more of a shared content-creation tool, while the greater flexibility of tablets, hybrids and lighter notebooks address users' increasingly different demands," said Gartner research director Ranjit Atwal.
Windows overall will do better, thanks to increasing sales of smartphones and tablets, especially the former. "The upside on mobile phone is so much bigger for Microsoft given the size of the market," Atwal said. "Even though Microsoft's share of mobile phone will remain small, the volume of that market is very large. The tablet market, on the other hand, is still small in comparison."
For 2014, Gartner predicted Windows device shipments of 360 million, a 10% increase over 2013's total of 328 million. Atwal expects Windows to pick up even more momentum in 2015, when the operating system should ship on 423 million devices, up 18% over the year before (and up 29% from 2013's relatively dismal 328 million).
Microsoft will have a tougher time generating growth from tablets than from smartphones, Atwal said. For 2014, Gartner has pegged Windows' share of the tablet market at between 4% and 5%, or 11-12 million shipped by all OEMs, Microsoft included.
But while Gartner was bullish on Windows' future, at least on a shipped device level, Atwal isn't certain that translates into success. Or profits. "Whether that growth is enough to sustain their investment, I don't know," he said. "That's the question."
Atwal was alluding to Microsoft's €5.44 billion acquisition of Nokia's handset business, a deal that has cleared major regulatory hurdles and will probably finalise this quarter.
Windows' troubles have been traced to fierce competition from tablets and smartphones for consumers' money, a trend that resulted in smaller shipment numbers for traditional PCs in both 2012 and 2013 as people let their notebooks and desktops gather dust, upgrading - if ever - at a much slower pace than before the explosion of mobile devices.
But when consumers do replace an aging PC, they're twice as likely to pick another personal computer, albeit one lighter and more mobile, than a tablet, showing that the PC remains important to some.
"Those who are looking to replace a PC - we call them 'engaged users' - want something better than they already have, so they're much more likely to look at lighter, thinner, touch-enabled notebooks," said Atwal.
In 2013 Windows devices accounted for 14.3% of the 2.3 billion total; that share will rise slightly to 14.5% in 2014 and then to 16.1% in 2015. Meanwhile, rival Apple lagged behind, ending 2013 with a 11.6% share. It will narrow the gap in 2014 with an expected 13.9% share, then see it widen again in 2015 when its share reaches 15.2%.
Windows' and Apple's shares - the latter a combination of both iOS and OS X, with iOS dominant - will continue to be dwarfed by Google's Android, which will power 38% of all smart devices in 2013, 45% in 2014 and 48% in 2015.
But none of Gartner's numbers are guaranteed. Both it and rival IDC revised their projections several times during 2013 to reflect worsening conditions for traditional PCs - and thus for Windows - resulting in once-optimistic estimates being tossed aside.
The same might happen in 2014.
But one trend was clear to Gartner: "People want devices that are more mobile than what they have now," said Atwal.