A very long process carried out primarily by users of the FAT16/FAT32 filesystems (ie. MS-DOS or Windows). It rearranges the physical location of files on a hard drive to ensure that all parts of the file are in one large block. Typically takes a very long time to complete, during which the computer is basically useless. Power failures during defragging usually cause data loss. Most modern filesystems, such as ext2, are designed to minimise fragmentation of files. In such cases, defragging is mostly eliminated (although some people still like to defrag their hard drives anyway).