Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Pen Computing refers to a computer user-interface using a pen (or stylus) and tablet, rather than devices such as a keyboard and a mouse. Pen computing is also used to refer to the usage of mobile devices such as wireless tablet PCs, PDAs and GPS receivers. The term has been used to refer to the usage of any product allowing for mobile communication. An indication of such a device is a stylus, generally used to press upon a graphics tablet or touchscreen, as opposed to using a more traditional interface such as a keyboard, keypad, mouse or touchpad.