CUPERTINO, Calif. » Apple says its next mobile operating system, iOS 7, will be available as a free download on Sept 18.

Craig Federighi, head of software at Apple Inc., said at an event at the company’s Cupertino, Calif., headquarters that "downloading iOS 7 is like getting an all new device."

The new system can be downloaded on the iPhone 4 and later models, as well as on the tablets beginning with the iPad 2.

Apple also says it expects to ship its 700 millionth iOS device next month. Apple CEO Tim Cook predicts that iOS 7 will become the most popular mobile operating system in the world.

The company is expected to unveil new phones later today.