It was not so long ago that we would tap away on a PalmPilot with a tiny stylus, or exercise our thumbs on a BlackBerry micro-keyboard. Then, in January 2007, along came the , and everything changed. Suddenly, people were wiping their fingers across screens, pinching images and performing other maneuvers that had not previously been part of the interface.

Now we not only take touch input for granted, we expect to be able to use multitouch (using more than one finger on the screen at a time) and gestures as well. What made this touch screen revolution possible, and where is it likely to take us?

Many paths to touch

To begin with, not all touch is created equal. There are many different touch technologies available to design engineers.

According to touch industry expert Geoff Walker of Walker Mobile, there are 18 distinctly different touch technologies available. Some rely on visible or infrared light; some use sound waves and some use force sensors. They all have individual combinations of advantages and disadvantages, including size, accuracy, reliability, durability, number of touches sensed and -- of course -- cost.