On start up, it reads the whole directory tree once and then presents it in three useful views: Please visit the WinDirStat blog for more up-to-date information about the program.
Note: if you are looking for an alternative for Linux, you are looking for KDirStat ( apt-get install kdirstat or apt-get install k4dirstat on Debian-derivatives) or QDirStat and for MacOS X it would be Disk Inventory X or GrandPerspective. WinDirStat is a disk usage statistics viewer and cleanup tool for various versions of Microsoft Windows. Latest version: 1.1.2 Windows Directory Statistics WinDirStat - Windows Directory Statistics
