Washington Post: Microsoft has unveiled the pricing details for Windows 8. If you currently use Windows XP, Vista or 7, upgrading to Windows 8 Pro will cost you just $39.99. That's significantly lower than the $199.99 it currently costs to upgrade to Windows 7.
According to NetMarketShare, 40 percent of PCs still run Windows XP, which is now more than a decade old. Thirty-nine percent of PCs run Microsoft's most recently released operating system, Windows 7.