Make it safer to use so that it does not overwrite boot sectors or damage the file system and system files required to start Windows.

I tried Advance Defrag once and was impressed with its relative speed and interface. But, when I rebooted later, I just got a black screen with a blinking cursor - had to do a full reinstall of Windows XP. Other brands of disk defragmenters do the same thing. Defragging a hard disk from within the Windows environment probably isn't such a good idea anyway.