A platesetter is a machine which configures a lithographic plate.
For the most part, there are three types of platesetters: Capstan, External Drum and Internal Drum. Capstan type platesetters feed plates through the imaging area at a set, continuous speed. Capstan devices are generally considered the most affordable, but least accurate method of producing plates. External drum platesetters work by having the plate affixed to the outside of a rotating drum. As the drum rotates, the imaging unit moves parallel along the length of the drum, imaging as it moves. An Internal drum platesetters work by having a plate set inside of the drum. The imaging unit, or a spinning mirror, traverses the center of the drum, imaging as it moves.
Plates are often hole punched by the platesetter. External drum units typically punch a plate then load it onto the drum, using the punches to ensure registration on the drum. Internal drum machines will load the plate, punch and image the plate, then release the punches, also to ensure registration.