The Disk Defragmenter feature has been renamed as "Optimize Drives" under Windows. To defragment your hard drive under Windows 8.
How To Defragment Hard Drive
Click on the Charms Bar
> Optimize Drives
. Next, the Optimize Drives dialog shall open, displaying the list of drives.
Then, select the drive of your choice (Note that: the Current status field will give you the % fragmented) and click on Optimize
The defragmentation process will start.
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