The idea is simple. Man would not be able to exist without language and writing. Sharing written and drawn information is the most important means of cultural exchange. But computers do not understand the most simple strokes of our beloved gestures.
Computers are actual illiterates when it comes to recognizing hand-drawn writing.
The ease of information manipulation would result in an intensified concentration on contents, with the user being freed from technical restrictions. The pen replaces a keyboard and other input devices. Were it not for the additional output capabilities, e.g. video and sound, bystanders would not necessarily recognize this as a machine but as a paper notebook. The computer is also able to recognize handwritten text, i.e. it can convert scribbles to printed text. Pen-based computers exist in various sizes and for a multitude of application classes.