Write precompensation (abbreviated WPcom in the literature) is a technical aspect of hard disk design. It is the use of a stronger magnetic field to write data in sectors that are closer to the center of the disk. In constant angular velocity recording, in which the disk spins at a constant speed no matter where the data is written, the sectors closest to the spindle are packed tighter than the outer sectors and so require a stronger magnetic field to write the data.
In the past one of the hard disk parameters stored in a PC's CMOS memory is the WPcom number, a marker of the track where precompensation begins. Modern hard disks rarely access the CMOS memory and internally store the WPcom number if write precompensation is used.