The full form of RCX is Robotic Command eXplorer. It’s used on Technology ,Robotics & Automation in Worldwide

The LEGO RCX brick (Robotic Command Explorer) is a large LEGO brick included in the LEGO Mindstorms kit that contains an embedded microcomputer that serves as the “robotic brain” of a robotic construction.  Students use LEGO bricks and other materials to build their construction around the RCX brick.  The programmable logic controller allows users to 

program functions that their LEGO creations will then be able to perform.  An infrared tower acts as a bridge between the computer and the brick. The RCX has three input connections (for attaching light, sound, and rotation sensors) and three output connections (for driving motors and lights), and an infrared communications port.  The IR port can be used to communicate with another RCX.  The LCD display on the RCX brick displays information about the motors and sensors along with data stored in the processor.  The RCX can be used by itself to power a relatively simple robotic device or can be linked to the infrared tower and other RCX bricks to control increasingly complex robotic creations.  “Because it does not need to be connected to the computer (the program can be downloaded through the tower), children have flexibility in the type of creations they can make, as well in deciding the behaviors of their projects” (Bers, 2008).

Newer versions of the RCX operate off 6 AA batteries, while older versions contained a 9VDC input for using optional AC power (Hystad, 2002).  Available from LEGO Education, the RCX can be purchased as part of a Mindstorms kit, or separately for about $100.00 (“Lego education: rcx programmable brick,” 2011).
 
The RCX brick can interface with Mindstorms software as well as with RoboLab, a software program designed specifically for using robotics in school settings.  Due to the widespread popularity of LEGO products with children, the RCX brick is a useful tool for practicing constructionism in the early childhood classroom (Bers, 2008).