defragmentation

In the maintenance of file systems, defragmentation is a process that reduces the degree of fragmentation, files that are stored in multiple segments that are not contiguous on the storage medium. It does this by physically organizing the contents of the mass storage device used to store files into the smallest number of contiguous regions (fragments, extents). It also attempts to create larger regions of free space using compaction to impede the return of fragmentation.

Defragmentation is advantageous and relevant to file systems on electromechanical disk drives (hard disk drives, floppy disk drives and optical disk media). The movement of the hard drive's read/write heads over different areas of the disk when accessing fragmented files is slower than accessing the entire contents of a non-fragmented file sequentially without moving the read/write heads to seek other fragments.