What is disk defragmentation and why should I do it?

Disk defragmentation is the process of reorganizing data on a disk drive so that all related pieces of a file are stored together. This improves disk performance because, when files are scattered all over the disk, it takes longer for the drive to locate all the pieces and read them into memory. By consolidating the parts of files together, disk performance and access times can be improved. Defragmenting your hard drive should be done regularly, as over time files become scattered and the drive must work harder to access them.