The 7-inch, 45 records were released in 1949 by RCA Victor. It was a smaller, higher fidelity, more durable replacement for the 78-rpm shellac disks.
45s really caught on in the early 60s and lasted into the 80s. Originally, record companies didn’t put a lot of weight on LPs, or albums. Their efforts were put into promoting singles, because that’s what the market bought. Elvis was initially on Sun Records and never put out an album.
In the 60s, albums became more important, often viewed as complete works, not just a collection of songs – think Sgt. Pepper. By that point, a 45 single was put out to garner interest in the album, which would contain the single, sometimes more than one. The Beatles always felt that was a bit of a rip-off for the fans, so they didn’t put singles on the albums, so the fans could get real value for their money, not buying the same recordings numerous times. Think how incredible Sgt. Pepper would have been with Strawberry Fields Forever and Penny Lane. both of which were recorded during the Sgt. Pepper sessions.
Often times, the record company would edit the 45 records single to fit to 3-minute format. They tried it with both Hey Jude and Bohemian Rhapsody, but neither The Beatles or Queen were playing that game! The 45 record picture sleeve is sometimes worth more than the record itself.