The data storage space on a disk is divided into discrete units. These units are called clusters. When files are written to the disk, they are broken up into cluster-sized pieces. When all of the pieces of a file are located in adjacent or contiguous clusters, the file can be accessed quickly.

Your computer's hard disk stores all of your files, applications, and the Windows operating system. The bits of information that make up your files gradually spread over the disk. This process is known as fragmentation. The more that you use your computer, the more fragmented the hard disk gets.


When a fragmented file is accessed, the disk performance is slower. The performance is slower because the drive head locates, loads, saves, and keeps track of all of the fragments of the file. If free space is also fragmented, the drive head might have to track adequate free space to store temporary files or newly added files.

Optimization rearranges file fragments into adjacent or contiguous clusters. When the drive head accesses all of the file data in one location, the file is read into the memory faster. Optimization also maximizes the usable free space on a disk by grouping most frequently used files and infrequently used files. Optimization consolidates free space to avoid fragmenting newly added files. It adds extra space after major data structures so that they can grow without immediately becoming fragmented again.