Apple has a commanding lead in the business selling 80 percent of all digital music via its iTunes Store, USA Today reported Wednesday.

Of a total of 6 million songs, iTunes, Apple's music library, now has 2 million songs without digital rights management, meaning the songs can be transferred to different digital systems.

Six months after opening its MP3 Store, Internet retailer Amazon has amassed a collection that includes 4.5 million songs, all without digital rights attached, the report said.

The move away from digital rights management began a year ago with Apple's deal for 150,000 songs owned by EMI Music.

Former EMI executive Ted Cohen now appreciates Amazon's role, which "removed some of the stranglehold iTunes had on the market," he said.

The new systems measure a shift in the music industry. Digital song sales grew from 189 million tracks in the first quarter of 2007 to about 239 million for the same period of 2008.

By comparison, CD sales declined to 74.3 million in 2008 from 89.2 million for a similar period of 2007.