I’ve always wondered how radio DJ’s talk to people who call in to the radio station live (supposedly) on the air, and then somehow manage to immediately play their requested songs. How do they do this so quickly? Do they have some sort of a massive supercomputer with every song known to man on it that has lightning-fast retrieval of songs? 
Or are these call-in’s somehow pre-arranged or pre-recorded? My guess would be the latter, but I’m not sure…
They take the call, tape you, then get the song qued up for when they are going to play your call. Most of the big radio stations do have the songs on a computer.
Note that for songs on the playlist, they’re going to get dozens of calls asking for it. So the DJ just has to tape an occasional caller and play it when the song comes up in the rotation.
This one is soooo easy to figure out.