In computing, a mouse (plural mice or mouses) functions as a pointing
device by detecting two-dimensional motion relative to its supporting surface. Physically,
a mouse consists of a small case, held under one of the user's hands, with one or more buttons.
It sometimes features other elements, such as "wheels", which allow the user to perform various
system-dependent operations, or extra buttons or features can add more control or dimensional input.
The mouse's motion typically translates into the motion of a pointer on a display.
The name mouse, coined at the Stanford Research Institute, derives from the resemblance
of early models (which had a cord attached to the rear part of the device, suggesting the idea
of a tail) to the common mouse.
The first marketed integrated mouse — shipped as a part of a computer and intended for personal
computer navigation — came with the Xerox 8010 Star Information System in 1981.
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. An early example of the trackball, perhaps the earliest,
was employed in the Canadian military's DATAR system.
When mice and trackballs still had chopper wheels, trackballs had 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. 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. Most trackballs now have
direct optical tracking which follows dots on the ball. Some mice, in place of a scroll wheel,
acquired a small trackball between the buttons, useful in maps and other circumstances calling
for scrolling in two dimensions.
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