The Magnetic Spacing Sensitivity of Perpendicular Recording

Perpendicular and longitudinal hard disk drives are compared in terms of their sensitivity to magnetic spacing. The heads in both drives have the same air-bearing design. When the ambient pressure is changed, both drives respond with the same change in spacing. The relative change in soft error rate and SNR as a function of spacing is the same for both types of drives. In addition, spacing is measured directly as a function of pressure. The Wallace spacing loss gives similar results for both designs in the limit where the reference wavelength is small relative to the distance between the head and the soft underlayer. The Wallace formula agrees as well with the hyperbolic formula that includes the effect of an ideal soft underlayer