Running disk defragmenter on Windows pc can go a long way in helping improve the performance of your machine. By defragmenting your hard drive you make sure that all the files on your hard drive are stored in consequent locations which means all the parts* of the file that it has been broken down by the operating system lie on one stretch, which makes it faster for the hard drive to access and display the file on your screen rather that when the parts of file are stored all over the place on the hard drive. So what defragmenter does is to make sure that all the parts of the file are located in one stretch.

To run defragmenter on your Windows XP machine you can go to Start > All Programs > Accessories > System Tools > Disk Defragmenter (click here to see image ). On the defragmenter window clicking on analyze button will show you how much your computers hard drive is fragmented and if it needs defragmention or not and if it does you can start defragmentation by clicking on defragment button (click here to see image). 

* According to different file systems and also depending on the size of the file it can be broken down into different numbers while writing it on the hard drive.