Edison's recording cylinders were the first to market. Just as Steve Jobs famously insisted on the dimensions of early iPad screens, Edison's design was based on a size allowing sufficient fidelity and length of recording. His wax recording cylinders were approximately the size of a #1 tin can and dictated the approximate speed of 70-80 rpm. The 78 record was actually standardized at 78.26 rpm, because most recordings at the time had been made at close to the top end speed of Edison's and the common size was set at 10" and 12" for recoding length of a song. The 78 speed was also based on commonly available motors at the time. By WWII, RCA developed smaller 7" 45 records, intended to play a single song on each side and its record players smaller, while CBS developed 33-1/3 LPs for longer classical recordings, using the same 12" size as earlier 78s. The speeds, relatively arbitrary, were based on the intended recoding lengths and reasonable playback quality of the recordings. 16-2/3 and even 8-1/3 rpm were short-lived LP formats used mostly for audiobook recordings where only telephone-voice-quality was necessary. Thanks, I enjoyed looking up these formats, unaware of the latter two.