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Computerworld - In the five months since its release, Windows 7 has captured twice the usage share that its predecessor, Vista, attained in the same time period, a Web metrics company said today.

According to NetApplications.com in Aliso Viejo, Calif., Windows 7 accounted for 9% of all operating systems in use online for the month through last Sunday. In comparison, Windows Vista had a 4.5% share five months after its late-January 2007 release to retail.

Microsoft Corp. shipped Windows 7 on Oct. 22, 2009.

Windows 7's trajectory has been faster than Vista's ever since its release; the newer operating system hit the 4% mark several months earlier than Vista did. By the end of January, Windows 7's usage share was 7.5%, also double the 3.75% that Vista enjoyed by the end of its fourth month.

"Looking at the trends, the [Windows 7] growth rate seems to be strong and consistent, with no visible decline," said Vince Vizzaccaro, executive vice president at NetApplications.

Vizzaccaro also noted that the difference in Windows 7's weekend and weekday scores has been increasing, a sign that "personal usage is growing faster than corporate usage, which fits the expectations," he said. In the past, Vizzaccaro has explained that the usage share of newer versions of Windows climbs on weekends, when a greater percentage of the computers online are home machines. Enterprises traditionally lag behind home users in the uptake of new versions of Windows.

Microsoft's operating systems accounted for a combined 92% of all operating systems powering computers that went online last month. Windows XP represented the bulk of that, with a 66.3% share, while Vista was running on 17.4% of the machines in the NetApplications study. Apple Inc.'s Mac OS X had a share of just 5.1%.

If the trends of the last three months persist, Windows 7 will overtake Vista as the second-most-popular operating system, behind No. 1 XP, by June.

NetApplications measures operating system usage by tracking machines that visit the 40,000 sites it monitors for clients, which results in a pool of about 160 million unique visitors per month.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, send e-mail to gkeizer@ix.netcom.com or subscribe to Gregg's RSS feed .

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