At its current growth rate, Windows 7 could replace XP in 2.5 years

It's been one year since Windows 7 launched to the world, and to celebrate the passing of the year, Microsoft has released some information about the milestones Windows 7 has passed.

Most importantly among them, Microsoft announced that 240 million Windows 7 licenses have been sold worldwide, which gives it a 17% global OS market share. Microsoft communications manager Brandon LeBlanc today said Windows 7 is "the fastest selling operating system in history."

Last August, market research firm Net Applications found that Windows 7 beat Vista in domestic market share just eight months after its release. But given the unfavorable light in which Vista was viewed, replacing it was the easy part.

The real task for Windows 7 is to replace Microsoft's decade-old mainstay XP, which continues to hold more than 60% of the OS market.

But looking at Net Applications' figures and comparing them with Microsoft's, Windows 7's trajectory could accomplish that task fairly easily, too.

If Windows 7's share equals 240 million units, then the entire OS install base shown above equals 1.41 billion; and XP's share equals 846.4 million units. So at its current rate of adoption (and without taking into account other operating systems or extenuating circumstances,) it would take only two and a half more years for Windows 7 to replace Windows XP.

That's fast, indeed.