Files download from share sites often end up spread out on your HD. Fresh downloads fill the empty spaces on the HD, and if you are downloading different files at the same time the peaces can end up sharing the same general area. The computer uses more RAM to read a file that is in peaces all over your HD. If one of these files is one you are using or uploading, it will eat more RAM than if it has been organized. I have 320 MEG of RAM and I defrag once or twice a week. After I defrag I use 50 to 100 fewer MEG of total RAM while running Xolox.