Microsoft Corp Chief Executive Steve Ballmer said on Tuesday the company has sold 4 million upgrades to Windows 8, signaling a strong start for its new operating system which launched on Friday.

Ballmer, speaking at a meeting for software developers at Microsoft's headquarters near Seattle, said hundreds of millions of Windows systems would be sold over the next year, and the company was seeing strong interest from business users.

Ballmer already said on Monday that Windows 8 was outselling the previous version, Windows 7, at the same stage after launch three years ago.

(Reporting By Bill Rigby)