When files are created and data written to the file, the operating system
allocates space for the file from the free cluster list. Over a period of time,
the clusters that are allocated to a file may no longer be sequential
(contiguous or one after the after) but scattered over the disk.
Why is this a problem? An operating system reads data from secondary storage in contiguous clusters more efficiently and faster than from non-contiguous clusters.
Windows operating systems such as Windows 95/98 provide a defragmentation utility that scans the file system for fragmented files and moves them to a contiguous space. This results in faster loading and accessing of files.