Growth of the HDD industry has in the past been explosive, as recording density effectively doubled each year. Yet, as shown in the table below, since 2003 this growth rate has radically slowed down, leveling off at about 30-40% a year. This slowdown has been attributed to difficulties in further increasing the density to meet continuing demands for ever-higher recording density. As a result, the HDD industry has continued to devise new technologies capable of allowing for higher recording densities. One such technology is the recording method known as PMR (Perpendicular Magnetic Recording).

PMR (Perpendicular Magnetic Recording) and LMR (Longitudinal Magnetic Recording) are recording methods. As indicated by their names, PMR arranges magnetized cells vertically while LMR does so in a horizontal fashion. This vertical arrangement allows PMR to record a greater number of data bits in the same area. The primary reason why density is limited through LMR is a result of what is called superparamagnetism. Superparamagnetism refers to the phenomenon by which magnetized materials move closer as the density increases, to the point where they eventually interfere with one another. As magnetized cells become unstable and as their magnetism changes direction, any stored data can be rendered unusable. By avoiding superparamagnetism, PMR enables one to further increase recording density. It is believed that PMR will reach a maximum recording density of 1 TB/in2 (LMR: 200 GB/in2).