Attaching a bulbous, glowing sphere to the top of a device is one way to make it stand out, but the PlayStation Move's ball isn't just for looks -- it's actually an integral part of the controller. Working in tandem with Sony's PlayStation Eye camera, which comes included with the Move bundle, the ball allows for 3-D motion tracking in real-time.
Inside the ball is an RGB LED, which means the sphere can light up with practically any color. When multiple Move controllers are used simultaneously (the PlayStation 3 supports up to four at once), it's easy to tell them apart by the color of the sphere.
The ball's primary function, however, is providing a visual reference for the PlayStation Eye. The PlayStation Eye is a USB camera that plugs into the PlayStation 3 system and captures video at a resolution of 640x480 at 60 frames per second. Those specifications translate into a very quick response time, meaning actions the PlayStation Eye perceives are displayed on the screen with minimal delay or lag [source: Sony].
Things get interesting when the Move comes into play: The PlayStation Eye has been programmed to recognize the exact size and shape of the ball on top of the Move remote. Once the Move controller is visible to the camera, it's able to detect the exact positioning of the ball in 3-D space. By tracking the size of the ball (and easily following it, thanks to the glowing LED) the PlayStation Eye can accurately tell where the ball is at any time.
In addition to tracking the ball's coordinates, the PlayStation Eye can identify human faces and perform head tracking -- once it recognizes the people in front of it, the Eye can accurately follow the movements of their heads, but not quite as accurately as following the Move's sphere -- after all, people don't come in an exact size and shape! This entire process can be carried out within the span of less than one frame of movement (out of 60 per second) thanks to the power of the PlayStation 3's processor [source: Joystiq].
The video interface isn't the Eye's only ability. It can also pick up audio via an array of four microphones. Primarily, though, the Eye's task is keeping up with the Move remote's location. But location only paints half the picture -- it takes a whole other mess of sensors to interpret the orientation and movements of the Move, and they're all packed tightly into the controller itself.