Core XY is a Cartesian arrangement that is rapidly growing in popularity. The movement on the XY gantry depends on a combined effect of X and Y motors, best explained here: http://www.corexy.com/theory.html. CoreXY is a parallel manipulator system, which means that the motors on a CoreXY system are stationary. Parallel manipulator systems give more rapid acceleration than serial stackup configurations like Cartesian-XZ-head. Compare 3D printers with a Core XY configuration below.