defragment

tool, file system /dee-frag(-ment)'/ (Or "defrag") To

coalesce files and free space on a file system.

As modern file systems are used and files are deleted and

created, the total free space becomes split into smaller

non-contiguous blocks (composed of "clusters" or "sectors"

or some other unit of allocation). Eventually new files being

created, and old files being extended, cannot be stored each

in a single contiguous block but become scattered across the

file system. This degrades performance as multiple seek

operations are required to access a single fragmented file.

Defragmenting consolidates each existing file and the free

space into a continuous group of sectors. Access speed will

be improved due to reduced seeking.

The rate of fragmentation depends on the algorithm used to

allocate space and the number and position of free sectors. A

nearly-full file system will fragment more quickly.

MSDOS and Microsoft Windows use the simplest algorithm to

allocate free clusters and so fragmentaton occurs quickly. A

disk should be defragmented before fragmentation reaches 10%.

(1997-08-29)