Have you ever gone to a file cabinet to get a file, but it was not where you had left it? That's kind what fragmentation does to your hard drive. Disk Defragmenter in Windows 7 arranges all of the folders and files on your hard drive, making it easier and faster for Windows to find your data. Disk Defragmenter can be run manually or on a schedule.
Click on the Start button, then All Programs, then Accessories, then System Tools.
Click on Disk Defragmenter. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
Note:
Here's another way to open Disk Defragmenter: Click the Start button. In the Search box, type Disk Defragmenter or defrag, and then, in the list of results, double-click Disk Defragmenter.
Click Defragment Now.
Disk Defragmenter might take from several minutes to a few hours to finish, depending on the size and degree of fragmentation of your hard disk. You can still use your computer during the defragmentation process.