Defragmentation : Why ? What ? How ?

Why do we need to Defragment  ... ?

Use reuse of files , deletion, modification creates fragments in the system . which makes the system slower..

Some useful Terms :
Defragmentation ::
n the maintenance of file systems, defragmentation is a process that reduces the amount of fragmentation. 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). It also attempts to create larger regions of free space using compaction to impede the return of fragmentation. Some defragmentation utilities try to keep smaller files within a single directory together, as they are often accessed in sequence.

Fragmentation ::
Fragmentation occurs when the file system cannot or will not allocate enough contiguous space to store a complete file as a unit, but instead puts parts of it in gaps between other files (usually those gaps exist because they formerly held a file that the operating system has subsequently deleted or because the file system allocated excess space for the file in the first place). Larger files and greater numbers of files also contribute to fragmentation and consequent performance loss. Defragmentation attempts to alleviate these problem.

Common countermeasures ::
Partitioning ::
A common strategy to optimize defragmentation and to reduce the impact of fragmentation is to partition the hard disk(s) in a way that separates partitions of the file system that experience many more reads than writes from the more volatile zones where files are created and deleted frequently.
Offline defragmentation
The presence of immovable system files, especially a swap file, can impede defragmentation. These files can be safely moved when the operating system is not in use.

Note ::
Windows System Restore points may be deleted during defragmenting/optimizing
Besides defragmenting program files, the defragmenting tool can also reduce the time it takes to load programs and open files.

Download :
http://www.filehippo.com/download_auslogics_disk_defrag/