Sony is the last of the big music labels to offer DRM-free tracks

Sony has announced a deal to put its entire catalogue of tracks on the Amazon MP3 store by the end of January.

All of the songs on Amazon's store will be free of controversial Digital Rights Management (DRM) controls.

In early January Sony announced a plan to sell gift cards that let customers download albums free of DRM.

Copy control

The deal means Amazon is now the only company offering tracks from all four big music companies free of DRM.

This makes the Amazon store a more significant rival for Apple iTunes which has long had a commanding lead over rivals in the downloadable music market.

All the 3.1 million tracks in the Amazon store are free of DRM software. In contrast, only songs from EMI and some independent labels are available via Apple's iTunes without copy controls.

In February 2007, Apple boss Steve Jobs called on record labels to stop using DRM in a bid to boost the popularity of downloadable music.

The Amazon MP3 store, which launched in September 2007, is only available in the US. There have been no announcements about when or whether the service will be expanded overseas.

Songs prepared in the MP3 format can be played on any portable music player. Tracks protected with DRM software are typically bound to one service or a particular portable player.

Although sales of downloadable tracks have doubled in a year in countries such as the UK, many music fans have been frustrated by the limits that DRM places on what they can do with the songs they have bought.

The copy protection systems have been used in an attempt to limit piracy and stop people getting hold of music via illegal file-sharing.