UltraDefrag is powerful Open Source defragmentation tool for Windows NT. It is very fast, because the defragmenting is done by kernel-mode driver. They are three interfaces to them: graphical, console and native. The GUI is very useful, because it represents your filesystem visually as a color coded cluster map. The console is another option for those that prefer the command line. It allows you to run UltraDefrag from the task scheduler and scripts. Finally, the native executable will run at boot time in a manner similar to chkdsk. The design of UltraDefrag is very simple. There are no skins and other unnecessary stuff. It is a small and powerful program! It can be used on Windows NT 4.0, Windows 2000, Windows XP, Windows Server 2003, Windows Vista and all of the 64-bit editions of Windows. Also check out Vista installation faq to see how to run UltraDefrag on Windows Vista without errors