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Invented by IBM, which has trademarked the name and patented the technology, the TrackPoint system was developed by Ted Selker and Joseph D. Rutledge of IBM's Thomas J. Watson Research Center and first used in IBM notebook computers. In principle, the pointing stick is a miniature joystick that's stuck between the G and H keys of a conventional keyboard. The pointing stick protrudes just two millimeters above the normal typing surface. Its position enables you to maneuver it with either index finger while the rest of your fingers remain in the home row. Because in normal touch-typing your fingers should never cross the G/H boundary, it does not interfere with normal typing. The selection function of mouse buttons is given over to bar keys at the lower edge of the keyboard, adjacent to the spacebar. Figure 21.2 shows the placement of the TrackPoint.
The nub—which typically is removable in case you wear it smooth—mechanically connects to a pair of solid-state pressure sensors mounted at right angles to one another. When you press against one side of the TrackPoint device, it senses the pressure you apply even though the nub itself does not move. The TrackPoint electronics and software driver convert this pressure data into an indication of relative motion. The harder you press, the greater the signal the pressure sensor generates and the faster it tells your computer to move the mouse pointer. The paired sensors give you two axes of control corresponding to moving the mouse along its X and Y axes.
The TrackPoint system has several advantages in addition to its favorable typing location. It is entirely solid state and sealed so it, like a TouchPad, is environmentally rugged. It has no moving parts to wear out, except for the pointing nub, which you can readily replace. The disadvantage is that many people find it unnatural to use until they have acquired experience using it.
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