What is disk fragmentation?

 The files on the hard drives are not entire units, they are file fragments that are saved on the hard drive whose addresses are saved to locate each file, when using the disk to sort these fragments it becomes a more difficult task for the system, therefore the computer starts to take longer when searching for files and consequently, it becomes slower, that is why defragmentation is used.

Defragmentation is the process by which the system reorganizes file fragments to facilitate the task of finding them, in this way the computer is optimized, the useful life of the disk is reduced and a little space on the hard disk can be freed up.

All of this only happens on mechanical hard drives (HDD) and not on solid state drives (SSD).