How Disk Defragmenter Works

The main goal of the Disk Defragmenter is to place every ?le in one contiguous
space,so when you access a ?le,it can be read in one stream.The tool will ana-
lyze the volume to determine to what extent the ?les on it are defragmented.For
FAT/FAT32 volumes,it checks the File Allocation Table (FAT);for NTFS vol-
umes,it uses the Master File Table (MFT).Both table types record the data blocks
that are used by each ?le,so the defragmenter can easily determine which ?les
are using discontiguous volume space.
After the Disk Defragmenter has analyzed the volume,it can defragment it by
going through the list of fragmented ?les,and every ?le is moved to a place of
suf?cient free storage to hold the complete ?le.If such a space is not available,it
will try to defragment the other fragmented ?les ?rst,assuming it can open up
more contiguous space.The Disk Defragmenter will move a ?le to the free space
that is closest to the size of the ?le.This means that it will move a ?le even it is
surrounded with free space,as long as there is a better ?tting piece of storage.
Remember that Disk Defragmenter has its limitations,especially because a run-
ning system will always be subject to storage changes.The best proof is running
two consecutive defragmentations,whereupon you will notice that it will make
changes to the volume.

You also will notice that after a defragment operation there will still be
pockets of free disk space.This occurs because the Disk Defragmenter is neither a
disk reorganizer nor a compacter.In general,defragmenting will improve your
system performance,because the process will improve average ?le access speed.
The Disk Defragmenter will not always defragment all ?les,and you should
not be surprised that at the end of the defragmentation if it reports that it was
not able to defragment small ?les,even if enough free space is available to do so.
Before you start wondering about the usefulness of Disk Defragmenter,we
should look to the purpose and intent of this tool and the limitations that come
with it.

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