The performance of games and graphics-intensive programs depends a lot on the graphics card, CPU, and memory - this a lot of people know. However, there is another factor in performance that is often ignored - the hard drive. Most games have a few large compressed files which hold the game's data. If those files are fragmented (and they often are), both performance and loading times will suffer a lot. Defragmenting those files is easy, quick, and will improve game performance a lot. They can be defragmented without having to defragment the entire disk.
There are many programs available for defragmenting separate files. Some good free ones are Defraggler, and a command line utility called Contig. Rapid File Defragmenter works the best, but it costs money.
In my case, for Supreme Commander, doing this has improved performance a lot, most noticeably loading times, which were now about four times shorter. My case is somewhat of a worst-case scenario; the data files had over 40,000 fragments.
