The primary function of the optional handler is to make plates available on demand to the imaging engine. A multitude of plates are stored inside cassettes and these cassettes are loaded into the handler. There may be up to four cassettes residing in the handler. Inside a cassette there may be a protective interleaf sheet, sometimes called a slip sheet, between each plate which is removed by the handler and discarded. The handler receives commands from the engine control sequencer which provides instructions as to what cassette needs to be accessed to make a plate available to the picker mechanism so the plate may be conveyed to the imaging engine. Conversely the handler provides status information to the engine to make full interaction with the system possible.