Windowing vs scrolling on a visual display terminal

To study a different star the astronomer moves his telescope. To study a different bacterium the biologist moves his microscope slide. In the case of the astronomer, it is the viewing instrument that is being moved, while in the case of the biologist it is the viewed object that is being moved. These scientists have no choice, the nature of their equipment requires that they operate in a pre-defined way. The user of a video display terminal (VDT), however, can be given a choice. The VDT user views a representation of an area of computer memory. In most cases the portion of memory the user wishes to examine is much larger than that which will fit on the screen at one time. For this reason almost all VDT's are equipped with some sort of “scroll function” that allows the user to display data that is located beyond the limits of the screen.