A trackball is a pointing device consisting of a ball housed in a socket containing sensors to detect rotation of the ball about two axes—like an upside-down mouse with an exposed protruding ball. The user rolls the ball with the thumb , fingers , or the palm of the hand to move a cursor . Large tracker balls are common on CAD workstations for easy precision. Before the advent of the touchpad , small trackballs were common on portable computers , where there may be no desk space on which to run a mouse. Some small thumbballs clip onto the side of the keyboard and have integral buttons with the same function as mouse buttons.

Advantages:

•  Easy precision.

•  It has the advantage of being in contact with the user's hand, which is generally cleaner than the desk or mousepad and doesn't drag lint into the chopper wheels.

•  Some mice, in place of a scroll wheel, acquired a small trackball between the ears, useful in maps, and other circumstances calling for scrolling in two dimensions.

Disadvantages:

•  The late 1990s advent of scroll wheels , and the replacement of mouseballs by direct optical tracking, put trackballs at a disadvantage and forced them to retreat into niches where their distinctive merits remained important.