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Windows Disk Defragmenter is a computer program included in Microsoft Windows designed to increase access speed (and sometimes increase the amount of usable space) by rearranging files stored on a disk to occupy contiguous storage locations, or 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.
Windows 2000, Windows XP, and Windows Server 2003 include a stripped-down licensed version of Diskeeper Corporation's (formerly Executive Software's) Diskeeper. Windows XP additionally shipped with a command line Defrag.exe utility.
The techniques used by the Disk Defragmenter are as follows:
1. Moving all the index or directory information to one spot. Moving this spot into the center of the data, i.e. one third of the way in, so that average head travel to data is halved compared to having directory information at the front.
2. Moving infrequently used files further from the directory area.
3. Obeying a user provided table of file descriptions to emphasize or ignore.
4. Making files contiguous so that they can be read without unnecessary seeking.
Windows Vista changes
In Windows Vista, Disk Defragmenter includes an option to automatically run at scheduled times using Task Scheduler and uses low CPU priority and the newly introduced low priority I/O algorithm so that it can continue to defrag using reduced resources (less CPU and disk read/write activity) when the computer is in use. The user interface has been simplified, with the color graph and progress indicator being removed entirely. It is also not possible to select which drives to defragment, though Windows Vista Service Pack 1 adds this feature.
If the fragments of a file are over 64 MB in size, the file is not defragmented if using the GUI; Microsoft has stated that this is because there is no discernible performance benefit since the time seeking such large chunks of data is negligible compared to the time required to read them.[5] The result, however, is that Disk Defragmenter does not require a certain amount of free space in order to successfully defrag a volume, unlike performing a full defragmentation which requires at least 15% of free space on the volume. The command line utility, Defrag.exe in Windows Vista, offers more control over the defragmentation process, such as performing a full defragmentation by consolidating all file fragments regardless of size. [6] Defrag.exe also does not require administrative rights. This utility can be used to defragment specific volumes or to just analyze volumes as the defragmenter would in Windows XP.
Disk Defragmenter is currently being maintained by Microsoft's Core File Services (CFS) team. The Windows Vista version has been updated to include the improvements made in Windows Server 2008 in Windows Vista SP1. The most notable of these improvements is that the ability to select which volumes are to be defragged has been added back. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
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