Microsoft to launch Windows 10

Microsoft's new Windows 10 operating system debuts tomorrow, as the longtime leader in PC software struggles to carve out a new role in a world where people increasingly rely on smartphones, tablets and information stored online. The launch will be accompanied by a global marketing campaign for an even.

Windows 10 is coming to PCs and tablets first, but it's also designed to run phones, game consoles and even holographic headsets. It has new features, a streamlined web browser called Edge and a desktop version of Cortana, the online assistant that is Microsoft's answer to Google Now and Apple's Siri.

Still, the company insists Windows 10 will seem familiar to users of Windows 7, the six-year-old operating system still running on most PCs. Microsoft and PC makers want to erase the memory of the last big update, 2012's Windows 8, which alienated many with its jarring, unwieldy design. Microsoft skipped the name Windows 9, as if to distance itself further from the last release. While many analysts believe Windows 8 made sagging PC sales even worse, it's unclear if Windows 10 will spur the industry back to growth.

Microsoft plans promotional events in several cities tomorrow, tied to a global ad campaign and a series of charitable donations. About 5 million people who enrolled in an earlier test program will be able to download Windows 10 right away. The company is also offering Windows 10 as a free download, any time over the next year, to anyone who has the Home or Pro versions of Windows 7 or 8 (but not the Enterprise versions used by big organizations).

The company wants to get the new software on as many devices as possible. Microsoft needs a large pool of users to convince independent programmers that it's worth their time to build useful or entertaining apps for Windows 10 devices.