Windows 7 passed Windows Vista for the first time in July, reaching 14.5% market share compared with its predecessor's 14.3% according to Net Applications.

The web analytics firm said Windows 7 needed just nine months to hit a mark that Vista took more than 21 months to achieve. Vista's share peaked at 18.8% in October 2009 and has been in decline since: the OS has lost 4.5 percentage points, or 24% of its peak share, since Microsoft launched Windows 7.

But the rate of Windows 7's increase during July - just 0.8 of a percentage point - was the smallest since it debuted last year. And despite Window's 7's perceived popularity, Microsoft has not been able to move users away from Windows XP as fast as the company would have liked.

Net Applications said XP accounted for 61.9% of all operating systems used last month, down just 5.9% since January. If that rate continues, XP won't drop under the 50% share mark until January 2012.

Combined, all editions of Windows accounted for 91.3% of the machines that connected to Net Applications' sites in July, a decline of just over one-tenth of a percentage point. Net Applications uses data acquired from the 160 million unique visitors who browse the 40,000 websites it monitors for clients.