The most distinctive feature of a PDA is its touch-sensitive screen. In contrast to many portable computers, a PDA (usually) does not not contain a traditional, large "QWERTY" keyboard (which would make it less portable). Instead, you use a stylus to tap on-screen for entering and accessing data. Although stylus handwriting recognition doesn't take long to learn, it has been one of the biggest issues many people have with PDAs. To overcome the limitations of stylus input and to remain fully portable, HP's engineers came up with a new - patented - idea: simply attach a "QWERTY" keyboard to your handheld!
The keyboard, which has a size and shape similar to the PDA, is divided into two separated sections, which are pivotally connected to the body and rotationally move between a closed and open positions. In a closed position, two keyboard sections are stacked on top of the body and can function as a protection cover. In the open position, they move together into a full alphanumeric keyboard which can then be used as an alternative to stylus input.
For a better illustration, have a look at the five attached images from HP:
Figure 1 depicts a
perspective view of a PDA with the keyboard in an
extended open position;
Figure 2 depicts a
perspective view of a PDA with the keyboard in an
open position;
Figure 3 depicts a
top view of a PDA with the keyboard in a
closed position;
Figure 4 depicts a
bottom view of a PDA with the keyboard in a
closed position;
Figure 5 decpits a
side view of a PDA with the keyboard in a
closed position.