The piano roll was designed to play back recordings on a player piano. The roll is characterised by its perforations, one hole for each note. It is pulled over a metal bar which is fitted with a row of punch holes. Each punch hole connects to a system of valves and membranes. When a hole in the metal bar corresponds with a whole in the roll, air sucks through the paper and the metal bar. This lifts a connected membrane and which in turn moves a hammer to hit the corresponding string.
The roles can be applied to a regular piano by use of a separate device, the piano player. The player piano on the other hand has the pneumatic mechanism built into the piano directly.
During the early 20th century it was very popular to record famous pianists on piano rolls for playback on the reproduction piano, which was the only instrument capable of such refined performance.
The advertising efforts of manufacturers such as the Aeolian Company popularised the player piano as an essential feature to every home. Catering not only to music aficionados with beautiful recordings but also to potential buyers with musical aspiration themselves.sources