The first generation of Lego Mindstorms was built around a brick known as the RCX (Robotic Command eXplorer). It contains a 8-bit Renesas H8/300 microcontroller as its internal CPU. It also contains 32K of RAM that stores the firmware and user programs. The brick is programmed by uploading a program (written in one of several available programming languages) from a Windows or Mac computer to the brick’s RAM via a special infrared (IR) interface. After the user starts a program, an RCX-enabled Mindstorms creation may function totally on its own, acting on internal and external stimuli according to the programmed instructions. Also, two or several more RCX bricks can communicate with each other through the IR interface, enabling inter-brick cooperation or competition. In addition to the IR port, there are three sensor input ports and three motor output ports (also usable for lamps, etc.). There is also an LCD that can display the battery level, the status of the input/output ports, which program is selected or running, and other information.