Is digital music making CDs obsolete? Not yet, says streaming service Tidal, which on Monday started selling CDs of Prince's new album.

The prolific pop legend released his latest album, "HitNRun Phase One," exclusively on Tidal last week as he hailed the possibilities of online services that can quickly put out his work.

In a tacit acknowledgement that many music fans still prefer physical copies, the album came out on CD on Monday -- and Tidal, in a rare move for an Internet-driven company, started selling the CDs on its site.

Tidal is also selling the album as a digital download, believed to be the first time the service, launched last year, has allowed users to purchase music without becoming subscribers.

The album was also on sale at brick-and-mortar record stores and as a download on iTunes, Amazon and other online outlets. But it was not available on rival online streaming services such as industry leader Spotify and Apple Music.

Prince, who has released three albums in less than a year, has long dodged music industry convention and in the 1990s would appear with the word "slave" written on his cheek to protest his label's contractual conditions.

Tidal, led by rap mogul Jay Z, has tried to promote exclusive content as a way to compete in the fast-growing streaming sector, which allows subscribers to listen to unlimited music on demand.

Revenue from digital music matched physical sales worldwide for the first time last year, although CDs remain the dominant format in several key markets, including Japan and Germany.