For other uses of this acronym, see also: Resale Price Maintenance
Revolutions per minute, usually abbreviated rpm, refers to the speed at which record albums are played.
The four standard speeds are 16-2/3, 33-1/3, 45, and 78 rpm. The first two are often just referred to as "16" and "33". 16-2/3 rpm was mainly used in recordings of books made for the blind, and otherwise not much used (it was also used in an ill-fated "Highway Hi-Fi" system marketed 1956-1959 by Chrysler which played 16-2/3 rpm records in automobiles). 78 rpm was the standard speed for records made before and during World War II. Immediately following WWII, the 78 rpm standard was discontinued and replaced by two new speeds, 33-1/3 rpm and 45 rpm. 33-1/3 rpm records were used for albums, usually 12 inches in diameter, containing multiple songs, while 45 rpm was used for singles, usually 7 inches in diameter, containing one song on each side. Despite its discontinuation, 78 rpm continued to be available as a selection on turntables well into the 1960s and 1970s so people who had them could continue to play them.