The Pandora player is a free, Web-based Flash application. You don't need to download anything to use it as long as you have Flash 7 or 8 installed on your computer. The only difference between the free service and the subscription service ($36 per year or $12 for three months) is the ads in the free version. Everything else is the same.
Pandora delivers a 128-Kbps stream of music, and it only works with a broadband connection. It derives its music license from the DMCA (Digital Millennium Copyright Act of 1998) guidelines for streaming Internet radio, and the digital rights management (DRM) scheme it employs is notable in a few ways. First, Pandora will never play a specific song on demand; if you add a song to a station, it will show up eventually, but Pandora can only work it in at random. Also, you can only skip 10 songs in an hour -- this is so you can't just skip to the song you're looking for. The license also limits the number of times Pandora can play a particular song or artist in a particular time period, and to this effect Pandora stores a list of the songs played on your station in your computer's Flash local storage so it knows what it has played already. It also stores your user data there so it recognizes you when you arrive at Pandora.com.
Probably the most interesting stuff going on behind the scenes has to do with the Music Genome Project that Pandora taps into. Unless you've got a degree in music theory, most of the Genome's terms of analysis are outside the realm of common usage, but it's still cool to check out some of the parameters it's using to determine which songs are genetic matches for your seed song or artist.
The Music Genome is not a single, homogenous set of traits. Different types of music require some different subsets of genes. There are four basic groupings within the Genome: pop, jazz, rap/hip-hop/electronica and world. According to Music Genome Project founder Tim Westergren in a Tiny Mix Tapes interview:
Speaking of profanity, an interesting side note: Pandora only plays the explicit version of songs. The people at Pandora discussed it at length and decided to stay true to the artists' original intentions. When you register for Pandora, you need to provide your date of birth, and maybe that's part of the reason why.
In the next section, we'll take a look at how the Pandora playlist is assembled.