Microsoft has been at the  top of the heap for almost as long as people have used PCs. They’ve  managed to sustain an overwhelming competitive advantage, even after a  decade’s worth of antitrust action and the astonishing transformation of  Apple into a profit-making machine that has built one billion-dollar  business after another while the entire rest of the tech industry is  stuck in neutral. Indeed, the presence of Apple and Google as direct  competitors suggests that maybe Microsoft is overdue to take a tumble. 
There is never a shortage of Apple-versus-Microsoft yammering in the  blogosphere, but I haven’t seen much in the way of actual data. Is Apple  really making a dent in Microsoft’s long-standing Windows monopoly? Are  mobile devices like the iPhone and iPad taking over tasks that used to  be done by PCs? Sales figures tell part of the story, but in my opinion  the best data comes from analyzing how devices are being used in the  real world. I went off in search of hard numbers, and I found them at  the same source I used earlier this year to measure Windows 7 adoption  rates (see When will XP finally fade away?).
 Net Market Share  publishes snapshots of PC usage based on data from 160 million visits  per month to its large collection of sites (the exact methodology is here).  Its monthly reports on operating system versions contain a wealth of  detailed information about even the most obscure OSes, and they’ve  tracked the performance of mobile platforms consistently for the past  three years. To compile the charts in this post, I went beyond the simple summary reports  and dug deep into the details, recording and cross-tabulating data for  desktop and mobile OSes from November 2007 until October 2010. I found  four unmistakable trends.
 Windows XP continues its steady decline. In early  2008, more than a year after Microsoft launched Windows Vista, Windows  users had emphatically rejected that upgrade. Fewer than 10% of Windows  users had switched, and nearly 5% of all Windows PCs in use were running  Windows versions older than XP. The Windows 7 story is very, very  different. One year after the release of Windows 7, it has made a  significant dent in the Windows user base, and those diehards holding on  to pre-XP versions have mostly surrendered. XP’s share of actual usage  has declined more than 20 percent in two years, and that trend is  accelerating.
 
Data provided by > Net Market Share
 There’s no evidence that the marketplace is abandoning Windows to any significant degree.  The overall share of Internet traffic from Windows PCs has dropped  slightly in the past two-and-a-half years, from 95.4% to 91.1%. But  that’s true across the board for competing desktop OSes as well. Linux  usage is down dramatically in 2010, to 0.85% from an all-time high of  1.08% in early 2009. Interestingly, OS X usage is also down, dropping by  roughly a quarter of a percentage point since a year ago, from 5.26% to  exactly 5.00%. In relative terms, that’s almost exactly the same  overall drop as the Windows platform has seen in the same period.
 Apple is still gaining on Microsoft, thanks to iOS-based devices. There’s  no doubt that the Mac has been a big success for Apple over the past  couple of years. While Microsoft was stumbling with Vista, Apple used a  very aggressive advertising campaign that resulted in considerable  growth of OS X usage, at least in relative terms. The Net Market Share  stats confirm that OS X’s share of Internet usage rose from 3.45% in  early 2008 to more than 5% last year.  As I noted earlier, the Mac’s  momentum has stalled (which might explain Apple’s sudden “Back to the  Mac” event last week). But Apple’s overall share of the Internet   continues to go up steadily, thanks to mobile devices like the iPhone  and iPad. Added together, Apple’s one-two punch of OS X and iOS has been  a clear winner. It will be interesting to look at these figures again  in a year.
 
Data provided by > Net Market Share
 The mobile Internet is growing at an astonishing rate. This  was the most fascinating set of numbers to me, and they’re also the  ones that should have Microsoft most concerned. Back in 2007, Internet  traffic from mobile devices was nearly nonexistent; today, mobile  operating systems account for nearly 3% of all Internet traffic. The  percentage of Internet usage on mobile devices has been doubling every  eight months or so. If you extrapolate that trend, it’s easy to imagine a  world in which mobile devices consume 20% or more of total Internet  usage within the next two or three years.
 
Data provided by > Net Market Share
 So where is all that traffic coming from? Not surprisingly, Apple’s  iOS-based devices are the leader in the mobile category, as measured by  usage, accounting for 42% of the total traffic from mobile sources. The  very close runner-up, at 37%, is a big surprise: Java Platform, Micro  Edition (Java ME), presumably running mostly on Nokia feature phones. Symbian is a distant third at 11%, with Android in fourth at 8%.
 We are indeed moving rapidly into a world where mobile devices are  taking over many tasks that were previously handled by PCs. The big  question is whether (and if so, when) that growth curve levels off. This  is a market that is only beginning to explode, which means things can  change very quickly. I’ll be looking closely at these monthly numbers  over the next year, especially with Microsoft jumping into this space so  aggressively with Windows Phone 7.
                                                                                               Ed Bott is an award-winning technology writer with more  than two decades' experience writing for mainstream media outlets and  online publications.