Microsoft Windows operating systems run the Disk Defragmenter utility to reduce the number of fragmented files on a hard drive. The utility helps improve the computer's performance by reorganizing the data blocks of each file so that they reside in contiguous locations in the storage device.

As the computer creates or deletes and modifies files, data that belong to particular files often break into fragments that reside in disconnected spaces in the storage device. This causes more disk head movement, which means the disk requires more time to read and write data. The Disk Defragmenter utility optimizes file placement in the storage device to help the disk get back its most efficient read and write speeds. The utility often offers an analysis feature to show how much fragmentation exists in the computer's storage device.

Recent versions of Windows have maintenance schedules to automatically run Disk Defragmenter, relieving users of having to manually run the utility. For instance, Windows 7 performs defragmentation once a week during an early part of the day. Users can change the schedule so that the utility runs on a daily or monthly basis instead. In addition, they can change at what time of day the utility runs, and which disk volumes must go through defragmentation.

Users who decide to manually run the Disk Defragmenter utility should back up their files beforehand and verify that the disk is free of errors. The utility must complete its task without interruption from other software and power outage.