Microsoft KB Archive/105068

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Defrag May Not Be Able to Defragment a Drive 100%

Article ID: 105068

Article Last Modified on 11/16/1999


  • Microsoft MS-DOS 6.0 Standard Edition
  • Microsoft MS-DOS 6.2 Standard Edition
  • Microsoft MS-DOS 6.21 Standard Edition
  • Microsoft MS-DOS 6.22 Standard Edition

This article was previously published under Q105068


In certain circumstances, Microsoft Defragmenter (Defrag) may be unable to defragment a drive 100 percent. Even after fully defragmenting a drive, you may receive a message similar to the following:

99% of drive C: is not fragmented.
Recommended optimization method:
Unfragment Files Only

Even if you perform a full optimization, the drive may not become 100% defragmented.


This problem occurs when there are unmovable blocks (clusters) on the drive and a movable file is made noncontiguous by one of these blocks. Defrag tries to fit files around the unmovable blocks so that the files remain contiguous, but it is not always possible to achieve a perfect fit.

In the following simplified example, the drive has only ten clusters and three files; file A has five movable clusters, file B has two unmovable clusters, and file C has two unmovable clusters:

   CLUSTER:  1   2   3   4   5   6   7   8   9   10
   FILE:     A   B   B   A   A   A   C   C   A
   STATUS:   O   X   X   O   O   O   X   X   O   O

   CLUSTER = The cluster number on the drive.
   FILE    = The file that occupies the cluster.

In this example, files B and C cannot be moved. Because there are not five contiguous, movable clusters on the drive, file A cannot be fully optimized and the drive cannot be 100% defragmented.

Although it appears you could work around this problem by making unmovable files movable, doing so is not a good idea. Many programs mark a file as unmovable because the program keeps track of the exact location of the file. Moving the file can cause the program it is associated with to fail. For example, some programs use unmovable files as part of a copy-protection scheme.

It is better to have a slight level of fragmentation than risk moving an unmovable file that should not be moved.

Additional query words: 6.22 6.20 6.00

Keywords: KB105068