For the first year it will be a free upgrade for current Windows 7 and 8.1 users, incluidng mobile. The investors were not impressed and share price dropped after the announcement.

Well a slight correction . . .

Terry Myerson, executive vice president of the operating systems group, said that anyone running Windows 7, Windows 8.1 or Windows Phone 8.1 will be able to upgrade for free to Windows 10 in the first year after the operating system launches. And he noted that it's not just a one-time upgrade -- Windows will continue to be upgraded for free for the life of the device.