Microsoft's Windows 7 reached a major milestone in July, while Apple's Mac OS X lost ground for the fourth straight month, a Web analytics firm said Sunday.
According to California-based Net Applications, Windows 7 passed Vista for the first time last month by posting a usage share of 14.5%, versus its predecessor's 14.3%.
Net Applications uses data acquired from the 160 million unique visitors who browse the 40,000 Web sites it monitors for clients.
Windows 7 has been on a fast pace to supplant Vista as Microsoft's -- and the world's -- No. 2 operating system, behind the nearly-nine-year-old Windows XP. By Net Applications' calculation, Windows 7 needed just nine months to hit a mark that Vista took more than 21 months to match.
Vista's share crested at 18.8% in October 2009 and has been in decline since: Vista has lost 4.5 percentage points, or 24% of its peak share, since Microsoft launched Windows 7.
Microsoft has not been shy about flaunting Windows 7's success, calling it the firm's fastest-selling operating system with more than 175 million licenses sold , and claiming that Windows 7 runs 16% of the world's personal computers.
But the rate of Windows 7's increase during July -- just 0.8 of a percentage point -- was the smallest since the new edition's debut.
And for all its success at selling Windows 7 , Microsoft has not had as much luck in moving users off Windows XP.
The aged XP accounted for 61.9% of all operating systems used last month, Net Applications said, a decline of six-tenths of a percentage point from June and down 5.9 points since the first of the year. But Windows XP's slide has slowed: In the second quarter of 2010, the operating system lost two percentage points, compared to 3.3 points in the first quarter. At that rate of decline, XP won't drop under the 50% share mark until January 2012.
Combined, all editions of Windows ran on 91.3% of the machines that connected to Net Applications' sites last month, a decline of just over one-tenth of a percentage point. Windows 7's growing use appears to have been key to that small slip and in a slowing of Windows' gradual decline: In the second quarter of 2010, Windows lost only one-fourth as much share as it did during the first quarter.
Meanwhile, Net Applications reported that Apple's OS X recorded its fourth consecutive month of share decline in July, losing nearly two-tenths of a percentage point, the largest single-month drop in over a year and a half.
Since the beginning of 2010, Mac OS X has lost share in five of seven months. It now stands at 5%, the same number as in February 2010 and off the operating system's peak of 5.3% in October 2009, the month Microsoft debuted Windows 7.
Net Applications' numbers don't equate to sales -- two weeks ago Apple reported it sold a record 3.5 million Macs in the second quarter -- but they do show that Windows 7 is fueling an even bigger PC sales boom relative to last year's usage share standings. Windows 7, for example, now powers three times the number of machines than does Mac OS X.
Not all is gloomy for Apple . According to Net Applications, the iPhone 's operating system accounted for seven-tenths of one percent of all OSes online in July -- not just mobile operating systems -- a 19% jump from the month before.
July was the first full month that the iPhone 4 was available in the U.S. and several other countries.
In a note on its Web site, Net Applications pointed out that the gain came amid reports of antenna and reception problems in the iPhone 4 throughout much of July. However, the company also said that the jump in share was "typical prior to the release of a major upgrade" as buyers delay purchases until a new version of an operating system or device is available.
Net Applications had a point. The first full month after the introduction of the iPhone 3G in the summer of 2008, iPhone usage share leaped 63%. Two months after the debut of last year's iPhone 3GS, its share was 20% above pre-launch levels.
Net Applications' operating system share data can be found on its Web site.
Read more about operating systems in Computerworld's Operating Systems Topic Center.