Windows Disk Defragmenter

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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.

History

Defragmentation has been part of disk optimization since disk optimization stabilized in 1975. Few, other than Norton (Symantec) and Microsoft, have shipped defragmentation programs separate from disk optimization methods.

MS-DOS up to version 5 and Windows NT through version 4 did not come with a defragmentation utility.

When Defrag, licensed from Symantec, was shipped for free with MS-DOS 6.0, the use of the alternative commercial products became less frequent, because customers were unable to justify the additional expense.

Modern versions of Windows include a stripped-down licensed version of Diskeeper Corporation's (formerly Executive Software's) Diskeeper.

In Windows Vista, Windows Disk Defragmenter includes an option to automatically run at scheduled times. (In previous editions of Windows, this could be achieved by using the Task Scheduler to invoke Disk Defragmenter with command-line switches.)

How it works

The purpose of Windows Disk Defragmenter 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. The used techniques include:

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 head travel to data is halved compared to having directory information at the front.
2. Clustering files around the directory area.
3. Moving infrequently used files further from the directory area.
4. Obeying a user provided table of file descriptions to emphasize or ignore.
5. Making files contiguous so that they can be read without unnecessary seeking.