Write precompensation (abbreviated WPcom in the literature) is a technical aspect of the design of hard disks, floppy disks and other digital magnetic recording devices. It is the modification of the analog write signal, shifting transitions somewhat in time, in such a way as to ensure that the signal that will later be read back will be as close as possible to the unmodified write signal. It is required because of the non-linear properties of magnetic recording surfaces.