What is the principle of Disk Defragmenter?

Disk defragmentation, is through the system software or professional Disk Defragmenter software to the computer disk during the long-term use of the fragmented and messy files to reorganize, freeing up more disk space, can improve the overall performance of the computer and speed of operation.
Disk fragmentation should be referred to as file fragmentation because files are scattered across different parts of the disk, rather than being kept in contiguous clusters of disks. After a hard drive has been in use for a period of time, due to repeated writes and deletions of files, the free sector in the disk is dispersed across the entire disk in a discontinuous physical location, so that the file cannot exist in a contiguous sector class. In this way, to read and write to the file, you need to go to different places, to increase the head of the move back and forth, reducing the disk access speed.
When the application requires insufficient physical memory, the general operating system generates temporary swap files on the hard disk and uses the hard disk space that the file occupies for virtual memory. The Virtual memory management program frequently reads and writes to the hard disk, producing a large amount of fragmentation, which is the main cause of disk fragmentation. Other settings, such as temporary files or temporary file directories that are generated when browsing information from IE browsers, can create a large amount of fragmentation in the system. File fragmentation generally does not cause problems in the system, but too much file fragmentation can cause the system to look back and forth when reading files, causing the performance of the hard disk to degrade, and to shorten the hard disk life.
Hard drives are like a house and need to be sorted out, to defragment the disk to use the "Disk Defragmenter" This thing, Disk Defragmenter can use the File allocation table (FAT) file system, the FAT32 file system and the NTFS file system formatted volumes to defragment. Disk defragmentation is the fact that the files on the hard disk are re-written on the hard disk so that the files remain contiguous.   only a continuous, frequent, read-write drive can cause damage to the disk, but defragmenting is not an injury to the hard drive, because most people do not tidy up every day, and the time of each finishing is also very short, and will not read and write to the hard disk for a long time. There's no need to be too concerned about defragmenting your hard disk's lifespan. It is recommended that you make disk defragmentation up to two times per month to keep your hard disk read and write at peak speed.
General Home users 1 months to tidy up, business users and the server half a month to organize

What is the principle of Disk Defragmenter?