a programmable LEGO microcomputer. It can power motors and lamps connected to its three output ports and receive information from sensors connected to its three input ports.

The Robot Command Explorer (RCX) is a programmable LEGO brick with 3 output ports, 3 input ports, an LCD information screen, and buttons to control its operation. Programs are downloaded to the RCX via infrared transmission. The RCX is the "brain" around which the robot is constructed.