Windows XP may be the last Microsoft operating system to hold a majority share, according to data from Web metrics company Net Applications.
At its peak, Windows XP powered more than eight out of every 10 computers worldwide. In November 2007, the earliest month for which Computerworld has Net Applications' data, XP accounted for 83.6% of all operating systems.
Although Windows XP's share has gradually declined since then, it still enjoys a slight majority: Last month, XP owned a 52.4% share.
The long lag time between Windows XP's release in 2001 and Vista's debut in late 2006 -- combined with Vista's stumble in the marketplace -- are the factors usually cited to explain XP's large-scale and long-term dominance.
Both conditions could be reproduced -- Microsoft might face future failures like Vista -- but the one least likely to happen again is the five-year gap between upgrades.
That's because Microsoft has taken to a three-year development cycle. Even though the company has been mum about a ship date for Windows 8, the operating system it showed off last week, most experts have pegged its release to the fall of 2012, or three years after Windows 7's launch.
With a regular cadence between upgrades, it's unlikely that any one edition of Windows will be able to duplicate XP's supremacy.
Forecasts based on Net Applications' numbers bear that out.
Using Windows 7's average increase over the last three months as a guide, Computerworld projects that the OS will top out with a 41% share in the third quarter of 2012.
After that, Windows 7's usage share will begin to decline as customers upgrade to Windows 8 or start buying new PCs with the OS pre-installed. That's what happened to Vista. The problem-plagued OS peaked at 19% in October 2009, the same month that Windows 7 launched. Since then, it has lost nearly half its share; in May Vista accounted for 10% of all operating systems.
By the third quarter of 2012, XP's share will have dropped to 38%, marking the first time the creaky OS will be behind Windows 7 in Net Applications' rankings. Meanwhile, Vista will have nearly vanished, with a share of just 4%.
In this scenario, Microsoft continually repeats the Windows 7 performance, where a new edition is rapidly adopted, comes near but doesn't cross the 50 percent bar, and then is supplanted by a newer version.
That pattern could be disrupted, of course, by any number of factors, including users refusing to upgrade to a future release, as they did with Vista, which in turn would boost the share of the just-prior edition.
Some analysts have said that's possible next year if businesses pass on Windows 8, either because they just recently migrated to Windows 7 or because they see few benefits in what experts have argued is a consumer-oriented Windows 8 .
Windows' faster release cycle will also impact Microsoft, which supports consumer-grade editions for five years and enterprise editions for ten.
Currently, Microsoft supports three versions of Windows: XP, Vista and Windows 7. If Windows 8 appears in the third quarter of next year, that number will climb to four, as XP doesn't drop off the support list until April 2014. With a new version appearing every three years and a 10-year support promise, Microsoft will return to the practice of managing four editions simultaneously.
The company has done that before, most recently last year. Until June 2010, it provided security updates for Windows 2000 in addition to XP, Vista and Windows 7.
But one analyst argued that Microsoft may need to pick up the pace even more, a move that would increase the number of editions that must be supported.
"They're dealing with two competitors, one the hyper-iterative Google, which seems to always be updating its software," said Wes Miller, an analyst with Directions on Microsoft, in an interview last week.
"The other is Apple, which is logistically iterative," said Miller. "They update almost by clockwork."
Apple annually updates iOS, the mobile operating system that powers the iPad, and has upgraded Mac OS X approximately every two years since 2003.
"You're in a constant race now," said Miller of software development. "I'm not sure if every three years is often enough."
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer , or subscribe to Gregg's RSS feed . His e-mail address is [email protected] .
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