A disk usage analyzer is a utility which helps users to visualize the disk space being used by each folder and files on a hard disk or other storage media. This type of application often generates a graphical chart to help the visualization process.
Disk usage analyzers are popular with system administrators as one of their essential tools to prevent important directories and partitions from running out of space. Having a hard disk with insufficient free space can often have a detrimental effect on the system's performance. It can even stop users from logging on to the system, or, in extreme circumstances, cause the system to hang.
http://www.linuxlinks.com/portal/news/article.php?story=20100920142851208