Why is it that songs use to not be played on the radio if they were over three m!
Question: And why did that change?
Answers: And why did that change?
The only addition to an excellent answer by Calast is to put some perspective on the dating.
The 45 really came into its own on Top-40 radio in the
mid-late fifties and into the early 70s. By the mid-late 70s, even the smallest of stations had switched to cartridges. These were more reliable and longer lasting and no way to scratch them. They also stored easily and the title info could be read without turning your head around at 45RPM ;<)
As the technology improved, some 45s, as early as mid-60s could handle more information (just as CDs have grown) and longer songs were played on Top-40. But thaey had to be blockbusters like "Light My Fire;" "Hey Jude;" "Whole Lotta Love" etc.
Even then some radio stations, in order to live up to their claim of "More Music," would insist the label release two versions. Some stations would play one version at night and the other (shorter version) during the day. That gave them more music plus more time for commercials.
By the late 60s, most stations were also playing 33RPM albums (LPs). In fact the turnbtables had been able to play 33RPM since the early 50s and most stations had the capability, there just wasn't the demand. Except on EZ Listening (or elevator music) stations.
Today almost everyone is on hard drives, but I yearn for the days of an excellent and very tight 45 slip-start.
-a guy named duh
It seldom had anything to do with radio, except that the purpose of playing songs on the radio was to encourage kids to buy records and play those songs at home. And songs were distributed on 45 RPM singles that had a physical limitation of about three minutes per side. So songs had to be written to that length limit, or else they would not sell in large quantity, which is what the record companies were after. Since the songs were all three minutes or less, that's what got played. Of course, the radio stations went out and bought equipment to play 45 RPM singles, but that's just the popular way music was delivered in the old days.
Why did it change? Harder question, really. Radio stations discovered there was a market for album-oriented rock, songs that wouldn't fit on a 45 and were only available on LP records and eventually CDs and other media. New media were invented (some of which have since disappeared from the marketplace, thankfully) that displaced 45s. FM took over from AM, and people wanted to listen to music in stereo (45s were monaural). Lots of factors killed the 45 RPM single, so no one cared about the three minute limitation any more. Artists cheered - it was pretty limiting to not be able to write a four minute song. Ah, the bad old days.