All pop songs may not sound the same, but most are close to the same length. So many songs are close to three minutes long that that length has become lore. This lore is so popular that the Beastie Boys even wrote a song about it. It's not easy to create a masterful pop song that will stick in the minds of listeners and repeat over and over again in just three minutes.

But where did the "three-minute rule" come from?

History of the three-minute pop song

A flat record made between 1858 and the late 1950s is called a "78" by vinyl enthusiasts and collectors. It's called that because the record spins at 78 revolutions per minute. The 78 disc severely limits the length that a song can be, because only so much music can fit onto the disc. The 78 comes in two sizes: a 10-inch that holds three minutes of music and a 12-inch that holds four.

In 1949, RCA introduced a 45 rpm disk that quickly overtook the 78 and made it obsolete. These 45s were better than 78s in numerous ways. They were made of vinyl instead of shellac, which made them more durable and more easily portable. They were also cheap to make and to buy, which made them easy to market to teenagers in the mid-1950s. Like the 78, the 45 also holds about three minutes of music (depending on the range of sound a song required and the depth of the groove in the disc).

For a band to get its songs played on the radio, it needed to have a 45. Artists complied. This invented what was known as the "single," for a record containing a single song. The 45 record was cheaper for Americans to buy than a full album and easier for radios to share, making the single in many ways the bedrock of American music.

The songs that came out immediately after the creation of the 45 defined American popular music for decades. All of Elvis's singles were sold on 45, for instance, as did the singles of The Beatles, The Rolling Stones, and Pink Floyd. The seven-inch 45 single carried rock and roll, Motown, R&B, psychedelia, and the British Invasion into American households.

Has song length evolved with technology?

It makes sense to assume that since the basis of the three-minute song was the 78 and then 45 rpm single, then songs would become longer as technology evolved.

And there have, of course, been bands that wrote songs longer than four minutes even before the music industry switched to CDs. Rush and Jimi Hendrix have both recorded 20-minute-long songs. Pink Floyd, Led Zepplin, and Bob Dylan all have 10-minute songs. In no way are long songs unheard of in music, but the average song length is still — even as the industry has evolved almost entirely to digital media — under five minutes.

Based on data derived from musicbrainz.org, we can determine the average length of a song based on the year of its release. It would be easy to say that as new technologies have been developed that allow for longer music, the length of songs has increased. But the length of songs had its biggest jump, according to this data, between the '60s and '80s, and very little has changed from the'90s to 2008, a time period when the technology of music changed drastically.

"What drives what is heard on the radio is an artist's desire to have their music hit the mainstream, and a record label's desire to profit from that," Steve Jones, vice president at the Canadian radio firm Newcap, told NPR. Newcap is a radio firm that recently debuted a Top 40 station that offers "twice the music," which really means it cuts hit songs in half to make them shorter.

Jones is right. The length of a song on an album doesn't matter for anyone except for the artist and fans, but a song that hopes to make money and be played on the radio simply has to be a certain length. Either that, or radio stations will edit the song down to the standard, making it three to four minutes, just like the 45.