Optimizing is defragging plus arranging the files in an optimum fashion for access efficiency based on usage and other factors. Most good defrag programs give you the choice. What happens with the XP defragger is it gets interrupted unless you disable all sorts of gee whiz automatic things in XP. Also, you need to fix your page file so that it doesn't dynamically change all the time. Every time it changes, and you have it on the C drive, it causes the defragger to start over. Also - if you have NTFS - your usable free space is a whole lot less than what you think it is. The MFT Reserved area can take as much as 25% of your free space, and the defragger is not allowed to use that area. If your drive is 80% full - you are at best marginal. Get a bigger drive or shuck some stuff. I like to keep a good 40% open with NTFS.