system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 How or where do radio stations get their music?

Do they buy the CD albums? Do they download the music online? How did they get the music in the early days when radio just started?
gpt
Six-year radio station employee here. 

Most commercial music stations have an agreement with a programming/distribution company like Dial Global. Every week, your station gets discs loaded with new music that fits your station's format (Top 40, adult contemporary, country, etc.). In exchange for these discs, the station plays what are called "barter" commercials. Their agreement with the distribution company may be 2 minutes per hour of commercial time, for example. The distribution company has sales people that then sell this nationwide airtime to big companies like Pepsi, Home Depot, etc. Every week, the station then gets a list of commercials to play in each of those 2 minutes per hour. This is how the distribution companies make money. The stations, of course, sell the rest of their alloted commercial time to local advertisers, which is how the station itself makes money. 

The station's program director likely also has a weekly phone conversation with someone at the distribution company about what songs they're going to add to the station's rotation that week. It's a negotiation process, so that the company can get the songs they want on the air, and the program director can make the station sound the way he/she wants, as they know the local market and what the local listeners want. Record labels and promoters are likely dealing with the guy at the distribution company, not the local program directors across the country. This is why radio station playlists are often very similar across the country. 

College radio is a different game. No distribution companies, just a lot of music promotion companies that send CDs and MP3s of new artists to college music directors every week. The promoters then have weekly phone conversations with each station's music director to try to get them to add the music that has just been sent to them to the station's rotation.