In the early days of the movie industry, there was no sound stored on the film. As the movie played, a lone musician sat on the bench of a huge pipe organ and played intricate music that would invoke the mood of the film.
The sound was so encompassing that it would paint vivid pictures in the imagination of those who watched and listened.
This organ was known then as the unit organ or "Unit Orchestra", because one man, the organist, could sound like a complete ensemble. Later, after many of these were installed, it came to be known as "The Theatre Pipe Organ". Today, we lovingly refer to it as "The King of Instruments", and indeed, it is.
On either side of the silver screen were special rooms, behind curtains, that were full of pipes. Some of these were as big as trees and others smaller than a golfer's scoring pencil. The bigger the pipe, the lower the note, from brilliant highs to room shaking bass.
Some of these pipes were made out of various metal alloys and others were fabricated from wood. All were driven by huge electric air blowers that supplied air under pressure to the chests the pipes were mounted in. Many folks who know of pipe organs have often likened these instruments to huge "boxes of whistles".