SAN FRANCISCO (AP) — Microsoft CEO Steve Ballmer can’t afford to be wrong about Windows 8.

On Thursday in New York, Microsoft will unveil a dramatic overhaul of its ubiquitous Windows operating system. If it flops, the failure will reinforce perceptions that Microsoft is falling behind competitors such as Apple, Google and Amazon as its stranglehold on personal computers becomes less relevant in an era of smartphones, tablets and other mobile devices.

If Ballmer is right, Windows 8 will prove that the world’s largest software maker still has the technological chops and marketing muscle to shape the future of computing.