Apple has sold in excess of 400 million songs since it launched its iTunes Music Store service two years ago.

The song aquisition rate is climbing exponentially, driven by Apple's huge and growing iPod community and the ease-of-use of its iTunes music software (available for Windows, as well as Mac).

Announcing the four new iTunes Music Stores this morning, Apple's vice president of applications Eddy Cue said: "The iTunes Music Store has revolutionized the way we discover and enjoy music, and is now selling more than half a billion songs per year."

This is a huge increase in demand - as of Apple's first annivresary of teh service on April 28 2004, the company had sold a relatively modest (in comparison) 70 million songs.

The launch of Apple's European stores helped drive things forward. Within a week of the launch of the first three such stores in June last year, Apple sold almost a million songs in one week - 450,000 to UK music fans alone.

iTunes broke the 100 million songs sold barrier a relatively short time ago, on July 12, 2004.