Fragmentation refers to the condition of a disk in which files are divided into pieces scattered around the disk. Fragmentation occurs naturally when you use a disk frequently, creating, deleting, and modifying files. At some point, the operating system needs to store parts of a file in noncontiguous clusters. This is entirely invisible to users, but it can slow down the speed at which data is accessed because the disk drive must search through different parts of the disk to put together a single file.
In DOS 6.0 and later systems, you can defragment a disk with the DEFRAG command. You can also buy software utilities, called disk optimizers or defragmenters,that defragment (remove fragmentation) from a disk.
Fragmentation can also refer to RAM that has small, unused holes scattered throughout it. This is called external fragmentation. With modern operating systems that use a paging scheme, a more common type of RAM fragmentation is internal fragmentation.This occurs when memory is allocated in frames and the frame size is larger than the amount of memory requested.