How often should you defragment your hard drive and what kind of impact on performance does having a fragmented hard drive have? Should I go by Microsoft's reccomendation when I do analyze in Windows XP Disk Defragmenter? When I have used Windows XP's built in disk defragmenter, a lot of times it says that there were files that could not be defragmented? I have heard that using another software program like Norton's Speed Disk would be able to defragment a lot more files on the hard drive? Is this true and what program out there is the best for defragmenting a hard drive out of all the ones you may know about, as I only have heard of Norton's Speed Disk, but I'm sure there are many more?