In the Golden Era of Top 40 Pop-Rock and similar formats, those of us in radio relied on the charts published weekly in Billboard or Cash Box, weekly newspapers that covered the amusement industry. By the 1960s, most of the space in those papers (and Billboard dominated) was devoted to radio programming, record sales, and jukebox operators. You can easily have a look at Billboard and its charts for yourself. Billboard compiled separate popularity charts for 45 rpm singles and LPs/tapes, and for various genres of popular music: pop/rock, soul/R&B, country, even classical. Various genres (easy listening, urban, hip-hop) were dropped or added as needed.

Radio stations had a music director, or at smaller stations, the program director himself, who would each week receive Billboard and then put hot new records into the rotation (and remove older ones). Of course, record companies desperately wanted to get airplay, particularly at the big-city rockers like WABC New York, WLS and WMAQ Chicago, and KPRC Los Angeles, as those would set off the self-perpetuating rise to popularity and a Top 10 listing. That desperation had in the early 1960s let to the payola scandals of actually bribing DJs and music directors. By 1970, The Man was watching and so most bribery was less audacious: promising that artists would appear at an ungodly hour as guests on the morning show, or concert tickets to be given away in on-air promotions. Casey Kasem's syndicated radio show American Top 40 was on a prominent outlet in almost every market, meaning an entire nation (of white teens) was passionately interested in who'd made it into the top spot that week. Some of the big-city rock stations published their own playlists as weekly "surveys."

By the mid-1970s, specialty formats with very tight rules were making headway in popular radio, and new publications like Radio & Records catered to this shift with their own charts. Billboard's listings became more accurate, with scientific polling techniques (and later, UPC reporting) replacing the previous "gut feeling" reports from record stores, radio stations, and jukebox operators. FM listening also finally became significant enough that most markets essentially saw a doubling of radio outlets. That, and changes in the musical landscape, led to the splintering of popular music that we have today. FM's obvious advantage for audio fidelity and Reagan-era regulatory changes led to the abandonment of most AM stations to sports, news, and talk shows, while MTV became (for a while) the nation's Top 20 music source.