One reason that disks get fragmented is due to the SWAP file and the fact that Windows can vary the size of this. It starts at one size and if the PC needs more, it can be enlarged. When you restart your computer, the SWAP file returns to its original, minimal size and frees up the HD space it was using. This causes fragmentation of the hard drive. If HD space is not an issue, then stop Windows from bing able to change its SWAP file size, just set it to the maximum values.