3. Defragmentation utility

Files are stored in memory. On a hard disk, memory is divided into chunks called 'sectors'.

When a file needs to be stored, the operating system looks for free sectors on the disk. However, these sectors are rarely sequential (i.e. next to one another), instead they are usually scattered in different places across the hard disk.

If a file is broken up ("fragmented") across too many separate memory sectors, it becomes difficult for the hard disk to access all of the pieces of a file in a timely manner. This can make the computer appear to be running slowly.

To prevent this, defragmentation utilities juggle the contents of memory sectors around to keep files together as much as possible. This ensures that the computer runs quickly and efficiently.