Why did records spin at 78, then 33 and 45 turns a minute?

Records spun at 78 revolutions a minute largely by accident, and the later speeds came from a hunt for longer sides and a format war: 33⅓ for the LP, 45 for its rival. The literature does not record why 78 was chosen: it apparently just happened to be the speed of one of the early machines, and it kept being used. Early discs ran anywhere from 60 to 130 turns a minute. In 1912 the Gramophone Company set 78 as its standard, based on the average of the records it was already selling, and by 1925 it was becoming standard across the industry.

The disc itself came from Emile Berliner, who made the first commercially sold disc records in the 1880s. The speed mattered because playing time is the length of the groove divided by the turning speed. A standard 10-inch disc at 78 rpm held about three and a half minutes a side, so most popular recordings were limited to that length.

Then came the "War of the Speeds". For two years, from 1948 to 1950, record companies and customers did not know which format would win. RCA Victor introduced a 7-inch disc turning at 45, with a much larger centre hole, as a rival to the 33⅓ rpm LP. In 1949 Capitol and Decca adopted the LP, and RCA Victor gave in and issued its first LP in January 1950. In the end the 12-inch 33⅓ rpm LP became the dominant format for albums. The big hole on the 45 made it easier for jukebox machines to handle.

The slower speed follows from the playing-time formula: a disc turning at 33⅓, less than half the speed of a 78, plays the same length of groove for more than twice as long.