Abstract
Current significant focuses of Hard Disk Drive (HDD) research and development are the next generation of recording technology and responding to the economic pressure from flash or solid state storage technology. The market share for flash storage has been gradually increasing for years in both high performance and mobile applications. Among the strongest factors for choosing HDDs are cost in $/TB and energy density in W/m 3 . Developers and researchers in solid state storage are working to improve in these areas as well. Common to future recording technologies (HAMR, MAMR, TDMR or BPM) is the consequently larger increase in radial density than linear density. In other words, the TPI will increase more significantly than BPI and the servomechanical design must improve dramatically to support future products. Traditional evolutionary approaches of internal disturbance reduction and controller enhancement will fall short when it comes to meeting the 1 MTPI challenge, largely because external disturbances are not under design control so they cannot be reduced to scale with track pitch. To reach 1 MTPI, HDDs will need evolutionary changes and will increasingly rely on other active elements such as sensors and controller stages to enhance the effective bandwidth of the control system. More effective use of sensors (new or current sensors) requires improvements in either SNR, or the correlation between signals and offtrack motion. Their usage is complicated because the market is sensitive to the cost per TB, and the cost per HDD. New recording technologies will add to HDD cost so using more and/or more complex sensors carries economic risk unless they can be added with minimal cost. As always with HDDs, the fundamental challenge remains: to improve performance within the current range of production cost.
