Computers write data onto hard drives into whatever open spaces are available on the disk. This can result in a file being broken up into smaller pieces that are stored in various locations, called “fragmentation.” Fragmenting slows down the drive, as the read head must bounce among those locations in order to access the file.
Under ordinary circumstances, this isn’t a huge problem, but if a drive is severely fragmented, access can slow down enough to impact audio or video file playback and recording.
Defragmenting is the process of rewriting the files on a disk into a single contiguous block. This maximizes the efficiency and file access of the drive.