Disk Defragmenter rearranges fragmented data on a volume (such as a hard disk or a storage device) so it will work more efficiently. For more information, see What is disk defragmentation?
In Windows 7, Disk Defragmenter runs at regular intervals when your computer is turned on, so you don't have to remember to run it. It's scheduled to run once a week at an early hour in the morning. However, you can change how often Disk Defragmenter runs, and at what time of the day.
Open Disk Defragmenter by clicking the Start button . In the search box, type Disk Defragmenter, and then, in the list of results, click Disk Defragmenter.
If you're prompted for an administrator password or confirmation, type the password or provide confirmation.
Click Configure schedule, and then do one of the following:
To change how often Disk Defragmenter runs, click the menu next to Frequency, and then click Daily, Weekly, or Monthly.
If you set the frequency to Weekly or Monthly, click the menu next to Day to choose the day of the week or month that you want Disk Defragmenter to run.
To change the time of day when Disk Defragmenter runs, click the menu next to Time, and then choose a time.
To change the volumes that are scheduled to be defragmented, click Select disks, and then follow the instructions.
Defragmentation can't be scheduled for solid-state drives (SSD), as well as some types of virtual hard disks (VHD). If you want to defragment a volume that isn't showing up in the Select disks dialog box, you can try defragmenting it manually. To learn how to do this, see Improve performance by defragmenting your hard disk.