In the early days of bowling, respotting the pins was a physically demanding job. There were actually people behind the lanes resetting the pins and sending back the balls.
Today there are amazing robotic devices that do all the pin setting. The automatic pinsetter, first patented by Gottfried Schmidt, was introduced by the American Machine and Foundry Company (AMF) in 1946. This first pinsetter was a monster, weighing nearly 1.8 tons and standing 2.7m tall.
Modern pinsetters are but a fraction of a size of their predecessors and much more intelligent — via Youtube