Defragmenting the hard drive is just one of the hassles of using Windows. Many users do not even know what "defragmenting" the drive means, and their computers may run slowly because of it.
Fragmentation is when files are split into different pieces and are stored on separate places on the hard drive. Over time, more files get split up, and this slows the computer down. To fix it you can use the Windows defragmentation tool. In Windows XP, go to the Start Menu —> All Programs —> Accessories —> System Tools —> Disk Defragmenter.