Windows 8 and Windows Phone users only
Source
A Guy
For a limited time, Microsoft is offering 100 free albums when you install the company's Music Deals app. That's pretty incredible, but there's a catch: only Windows 8 and Windows Phone users can take advantage of the giveaway. Also, it's kind of a pain to get the albums, at least on a PC. (I haven't tried on a phone.)
It's well worth the effort, though, as the freebies include lots of big-name artists: Eminem, U2, Katy Perry, Norah Jones, Mumford & Sons, James Taylor, the Rolling Stones, Green Day, Ellie Goulding and so on. Most of the albums are at least a year or two old, but that doesn't make them any less appealing.
Source
A Guy