Just how does Shazam work?

I found this editorial to be quite interesting, just how does Shazam work. "Many of us are prone to using the Shazam music-identification service whenever we encounter unfamiliar songs. After all, it's just so easy to whip out our phones, open an app, and know everything about a mystery song in seconds. But how does Shazam gives us all this information so quickly?" Read in full.