Microsoft's Windows XP shed a large amount of usage share again last month as users continued to desert the decade-old operating system for Windows 7.
Windows XP lost 2.4 percentage points of share to post a December average of 46.5%, a new low for the aged OS in the tracking of Web metrics firm Net Applications. The month's fall nearly matched the record 2.5-point drop of October.
In the four months from September to December, XP jettisoned more than 11% of its share as of Sept. 1, falling by nearly six percentage points during the period.
The four months prior to that -- May through August -- XP lost only 3.4 points, or about 8.5% of the share it owned as of May 1.
Windows 7 has been the beneficiary of XP's decline, gaining 2.4 percentage points last month to reach 37%. In the same four months that XP lost 5.9 points, Windows 7 grew by 6.4 points, taking up the slack from not only Microsoft's oldest supported OS, but also the hapless Windows Vista.
If the usual trend repeats, Windows XP will lose an even larger chunk of usage share this month: In both 2009 and 2010, XP's share fell 40%-48% more in January than it did the previous month, most likely because of year-end purchases of new PCs equipped with Windows 7. With that in mind, XP's share could plummet by as much as 3.5 points this month.
The acceleration of XP's decline shows that users have gotten Microsoft's message that the operating system should be retired.
In July, Microsoft told customers it was "time to move on" from XP, reminding everyone that the OS would exit all support in April 2014. Before that, the Internet Explorer (IE) team had dismissed XP as the "lowest common denominator" when they explained why it wouldn't run IE9.
Two months ago, as Microsoft quietly celebrated the 10th anniversary of XP's retail launch, the company touted the motto "Standing still is falling behind" to promote Windows 7 and demote XP.
XP's hastened waning -- of the 12.4 percentage points it lost in the last 12 months, almost half came in the last four -- changes the date when the old OS will likely lose its primary spot in the Microsoft ecosystem.
Projections based on Net Applications' data now indicate that Windows 7 will become the most widely used version in April, several months earlier than previous estimates.
By the time Windows 8 debuts -- October seems the most probable on-sale date -- Windows 7 will have captured between 50% and 52% of the operating system usage market.
Windows 8's share also grew very slightly last month to 0.05%, or five PCs out of every 10,000, from 0.03% in November. That OS has yet to enter beta -- Microsoft has set the release for late February -- but a developer's preview has been available for three and a half months.
Net Applications calculates operating system usage share with data obtained from more than 160 million unique visitors who browse 40,000 Web sites that the company monitors for clients. More operating system stats can be found on the company's site.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed . His e-mail address is email@example.com.