Microsoft on Tuesday took the wraps off its second attempt to make a dent in Apple’s dominant position in the digital music business, a year after its first salvo fell far short of offering a serious challenge to the iPod.

At the same time, Bill Gates, chairman, sought to forestall any doubts about Microsoft’s willingness to keep taking losses in its pursuit of Apple, as he promised there would be more future generations of Zune, the software company’s digital music technology.