The trouble with miniaturization is that input can be difficult without a proper keyboard. This has been a problem for PDAs ever since they first appeared, and it gets worse as devices become smaller. A typical mobile phone may have no more than 12 small buttons, while tablet-sized devices may have none at all. Mice are even harder to implement without a desk to roll them over, so even laptops large enough to accommodate a comfortable keyboard usually rely on touch-sensitive pads or small sticks instead.
The keys on a full-size, typewriter-style board measure 19 mm square and can be pressed down at least 3 mm, shown in Figure 10.2. This means that the keyboard needs to be at least 200 mm wide for the Qwerty layout alone, ...