Apple's hit online music service iTunes has been made available to millions of PC-using fans for the first time.
The software, which offers tracks for 99 cents (60p), was launched for the Windows platform in the US.
It had previously only been available to users of Apple Mac computers - who bought 13 million tracks in six months.
iTunes' expansion is part of a plan to corner the growing market for legal online music, and is expected to become available outside the US next year.
It will boast a catalogue of more than 400,000 songs by the end of October.
Despite only being available for the Mac so far, iTunes accounted for 70% of all legal downloads as of last week, Apple chief executive Steve Jobs said.
But Windows-based PCs account for more than 90% of home computers, while Macs have a 5% share.
Jobs also set the target of selling 100 million songs by the service's first anniversary at the end of April 2004.
Internet and music companies are battling to win over fans to new legal download services and away from other hugely popular but unauthorised sites.
Napster is to be relaunched as a legitimate paid-for service at the end of October, four years after it burst onto the scene as a free, unsanctioned site.
And other websites like MusicMatch, BuyMusic and MusicNow have also launched pay services, with more on the way.