The Optimize option lets you optimize your boot volume to improve the boot time of your computer. Optimization of your boot volume maximizes the usable free space by rearranging file fragments into adjacent and contiguous clusters. When the drive head of your hard drive accesses all of the file data in one location, the file is read into the memory faster.

When you use the Optimize option in Windows XP, Norton Internet Security optimizes only the boot volume (for example, C:Windows). Therefore, it requires less time to complete optimization. However, when you use the Optimize option in Windows Vista or Windows 7, Norton Internet Security optimizes the drive that contains the boot volume. Therefore, it requires more time to complete optimization.

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.