Contrary to popular opinion, Windows XP is still the dominant OS worldwide after more than 10 years, but Windows 7 continues to narrow the gap. XP ended last year with a 46 percent slice of the OS market, according to December data from NetApplications. Although impressive after a decade, that number proved a hefty drop in use for XP, which kicked off 2011 with a 55 percent share and has fallen each month since then. On the upswing, Windows 7 rang out the year with almost 37 percent of the market, a solid gain from 22 percent last January and further proof of its ongoing monthly growth. In third place was Windows Vista, which dropped to 8 percent from more than 11 percent at the start of 2011.