What does defragmentation consist of?

When you copy a file to the hard disk, Windows looks for a free space to copy it to and places it there. Additionally, when you delete a file from the hard disk, it leaves a gap that Windows will use to copy a new file to, etc.
 

A file is fragmented when Windows tries to copy a file to an area that is too small to accommodate it completely. In these cases, Windows fragments the file into pieces so that it fits in the gaps available on the disk.  
 

This should not be a problem, however, over time, fragmentation can become excessive and slow down the computer. This is because Windows must look for all fragmented sections of a file every time it tries to access it.
 

For this reason, it is advisable to defragment the disk regularly.
 

Defragmenting consists of rewriting files so that all of their fragments occupy adjacent sectors on the disk, thus improving data access speed.
 

Note: Before defragmenting the disk, it is advisable to clean up all unnecessary files.