The 25mm IBM Trackball Keyboard is the second of two variants of the IBM's trackball-integrated Enhanced Keyboard variants. The Model M5-2 contrasts the Model M5-1 in being far more common and housing the trackball module in its own assembly on the top-right corner of the keyboard. The module also has the four mouse keys repeated facing the behind the keyboard to accommodate users using their thumbs for the trackball. The Model M5-2 remains in production via Unicomp as the Classic Trackball keyboard (also previously called "On-The-Ball").