There is also 16 RPM. You will find some vintage German Dual Turntables that play all four formats....
Why 78rpm, 45rpm, and 33.3rpm?
Does anyone know why these particular speeds were chosen for phono records? Early on there were 80rpm (one-sided) records, and 16 rpm was used for radio broadcast transcription and speech. I think that the CD sample rate 44.1 KHz has something to do with compatibility with movie frame rate. (The CD rpm varies as the disc plays so as to maintain a constant data rate).