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You can find this by clicking the Start menu, selecting All Programs, then Accessories, then System Tools. Select Disk Defragmenter from the list. You will need to have administrator access to run the Disk Defragment utility. You can also open the Disk Defragmenter utility by clicking Start then Search. Type “disk defragmenter” into the field and click Search. There will be a list of drives that are attached to your computer. Select the drive that you would like to defragment. This is typically the C: or D: drive. Click the Analyze button to see if the drive needs to be defragmented.  You can compare the graphs below the list of drives to see how defragmenting the drive will affect its space allocation. If you see a lot of red lines, that means you have a significant amount of file fragmentation.    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/0\/01\/Defragment-a-Windows-XP-Computer-Step-5Bullet1-Version-2.jpg\/v4-460px-Defragment-a-Windows-XP-Computer-Step-5Bullet1-Version-2.jpg","bigUrl":"\/images\/thumb\/0\/01\/Defragment-a-Windows-XP-Computer-Step-5Bullet1-Version-2.jpg\/aid1031512-v4-728px-Defragment-a-Windows-XP-Computer-Step-5Bullet1-Version-2.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/en.wikipedia.org\/wiki\/Fair_use\">Fair Use<\/a> (screenshot)<br>\n<\/p><\/div>"}  You must have at least 15% free space in order to defragment the drive. This is because files will be moved around in order to optimize the drive, and the system needs a place to temporarily put files that are being reorganized. Select the drive and click Defragment. Confirm that you wish to start the process in the pop-up window. After the process is complete, you will receive a report in a new window. This report will tell you which files were moved, and which couldn’t be moved, as well as your new free space readings.  Avoid using your computer during the disk defragmentation process. If you alter any files, the defragmenter may have to start over. You can watch the process by following the status bar at the bottom of the window. This will show you how far the process is, as well as what is currently being moved. The “after defragmentation” graph will adjust during the process as well.

Summary:
Open the Disk Defragmenter utility. Select your drive. Defragment the drive.