Disk defragmentation?
As you save and delete stuff on your hard disk, it will eventually be scattered around. Say, you had files A,B,... saved like this (x is for empty space):
AAAAABBCCCCDDEEEEExxxx
Then you delete files B and D:
AAAAAxxCCCCxxEEEEExxxx
and save file F which takes space of 5 there:
AAAAAFFCCCCFFEEEEEFxxx
Now the file F is all over the place and handling it is slower than if it were not.
Defragmentation is putting the files neatly together.
As you save and delete stuff on your hard disk, it will eventually be scattered around. Say, you had files A,B,... saved like this (x is for empty space):
AAAAABBCCCCDDEEEEExxxx
Then you delete files B and D:
AAAAAxxCCCCxxEEEEExxxx
and save file F which takes space of 5 there:
AAAAAFFCCCCFFEEEEEFxxx
Now the file F is all over the place and handling it is slower than if it were not.
Defragmentation is putting the files neatly together.