I'm not sure what the current exchange rate is, but at one time a picture was purported to be equal to a thousand words. So here's a picture of the hard drive of one of my computers:
OK, so actually it is a graphical representation of the files on the hard drive. Each colored block represents a single file. The colors and block size have meaning: The color indicates the type of file and the size indicates the number of bytes relative to the other files. This wonderful visualization is produced by the program WinDirStat (Windows Directory Statistics) that you can download from a link on that page. What makes this a useful tool is for those occasions when you need to free up space on crowded hard drive. By examining the Treemap created by WinDirStat, you can quickly discover what files, and types of files, are hogging all the space on the drive.
Take the large green block in the upper right of the picture. Selecting that block reveals it is a GPS update program I downloaded a couple of months ago. The file is occupying 2.1 gigabytes of space that could be used for something more useful. A press of the delete key removes the file, but not before a popup window first questions your technical competency. (It begins by asking, "Do you know what you are doing?")
WinDirStat is freeware and runs on Windows 95 (IE5), Windows 98 SE, Windows ME, Windows NT4 (SP5), Windows 2000, Windows XP, Windows Server 2003 and Windows Vista. It probably runs on Windows 7 too.