Apple's director of marketing consumer applications, Peter Lowe, confirmed the plans in an interview with a top digital-media analyst.
Lowe said, "There is a broad set of stuff that needs to be supported. We are working away at it and are on track to deliver it by the end of the year. Developing Windows software can be a challenge at the best of times, as there are so many configurations of Windows PCs and connectivity peripherals."
Discussing the response to the service, Lowe added: "It has been more successful than we hoped. Some of our music partners hoped for a million sales in the first month. We sold over three million tracks in the first month."
Apple's triumph in a traditionally tricky area has boosted the entire market. While Lowe didn't discuss extending the company's service to other territories, the impact has already been felt in Europe and the UK.