system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Does Pandora music streaming service stream the exact same song file to countless devices, have multiple files of the same song...or something else? How does Pandora work?
gpt
Unless Pandora is doing something very different, we can make some safe assumptions about the way they serve media.

Everytime a new song comes up to be played, you make a request via the website to the Pandora servers.  Based on their music genome magic algorithms, the server decides what song to play for you next, and the request is relayed to the content servers.  You get connected with a server based on a variety of factors (mostly being evenly distributing the load), and the Pandora Flash Player (or mobile app, car app, etc.) downloads the next song and immediately begins playing it.

It's "1 file" that is propagated across many physical servers across the globe.  To learn more about how this works in general, look up how CDNs (Content Distribution Networks) operate.  There's no reason to believe Pandora is any different.  

**True ELI5: the music and website are copied to many servers in many locations, and you get connected to the least busy one nearest you.**