Posted 14 April 2009 - 06:24 AM
Defragmentation of free space is also known as compaction. Strictly, defragmenting files reassembles those files that are in more than one segment, so they are contiguous (composed of a single block of sequential drivespace). It doesn't address the physical location of the files on the drive, so there can be empty gaps remaining, meaning the free space on the drive is fragmented. Compaction moves the position of files so they nestle together without empty gaps between them. Compaction is complex and time consuming, especially if the drive is nearly full, so most defragmenters compromise by performing modest compaction, but don't worry about some free-space fragmentation. (In some specific instances with the NTFS file system, modest free-space fragmentation actually enhances performance.)
Initiating defrag of free space will will cause every possible file to be re-located to give the largest possible amount of contiguous free space that can be made available. For average home or office purposes, this normally will not achieve a worthwhile benefit. But if you want to prepare for something like recording a large video file, and the drive is getting full, then defragging the free space first could mean the difference between a clean recording and a fragmented file that glitches.
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