I can remember months when total copies sold ranged between 20 and 25 million per month earlier in the sales cycle, but that’s still pretty darned impressive. Considering that 400 million copies of XP were in use in January 2006 and that Microsoft stopped selling this incredibly popular Windows version in January, 2009, it’s possible that there may be more than 600 million copies of XP still in use today, but I’d be surprised if there were more than 800 million overall. These waters are also muddied somewhat by Microsoft’s Windows XP Mode giveaway, which puts a free copy of a Windows XP VM into the hands of any owner of Windows 7 Professional, Enterprise, or Ultimate who decides he or she wants one.

Last month’s Desktop Operating System Market Share numbers from NetMarketShare.com (May, 2012) seems to bear out my analysis. It still shows XP with a 3.34% edge in marketshare over Windows 7, with all other OSes combined comprising less than 15% of all desktop seats:

NetMarketShare Distribution for May 2012 For Desktop OSes

Windows 8 will certainly make all of this extremely interesting, probably right about the time that Windows 7 celebrates its third birthday this October. My guess is that Windows 7 will surpass, and quite possibly even eclipse, Windows XP, sometime in the next two to three years. Whether Windows takes off and runs in Windows 7 fashion, or limps along as Windows Vista did instead, is still anybody’s guess. But even though most of the experts I respect have learned to appreciate Windows 8 (especially Paul Thurrott and Ed Bott) though I don’t think anybody is expecting it to be as successful as Windows 7 has been, is right now, and will continue to be.