Disk Defragmenter is a computer program included in Microsoft Windows designed to increase access speed by rearranging files stored on a disk to occupy contiguous storage locations, a technique commonly known as defragmenting. The purpose is to optimize the time it takes to read and write files to/from the disk by minimizing head travel time and maximizing the transfer rate. As of Windows XP, Disk Defragmenter is also used to improve system startup times*

Auslogics Disk Defrag is one of the best and fastest defragmenter that I have found. Supporting FAT 16/32, and NTFS file systems it is supplied with advanced optimization techniques.

QUICK TIP - when you run Auslogic you can choose a standard defrag or defrag & optimize. Choosing defrag & optimize will place the most frequently used programs in the quickest part of your hard drive (this is a longer processes however)