It is often helpful for computer users to see a visual representation of the file structure on their computers. The "explorer" in Microsoft Windows is an example of such a system. Before the days of graphical user interfaces, however, such visual representations were not possible. The best that could be done was to show a static "map"of directories and files, using indentation as a guide to directory contents. For example:
ROOT
| DIR1
| File1
| File2
| File3
| DIR2
| DIR3
| File1
File1
File2
This shows that the root directory contains two files and three subdirectories. The first subdirectory contains 3 files, the second is empty and the third contains one file.