Serving as an important data storage medium for information and data processing systems, hard disk drives (HDD) are once again called to increase recording density toward regions of multi-terabyte (TB) per inch square to meet the ever-increasing demand for information storage. With such demand, requirement for high accuracy in positioning magnetic read/write elements on spinning magnetic disks for data accessing and recording has been rigorous and is now reaching down to sub-nanometer range, which motivates extensive research and development for advanced mechanical and servo systems applied in HDD. This paper will first conduct an overall review of magnetic recording mechanism in terms of position error signals (PES) in HDD. Secondly, repeatable runout (RRO) component of PES will be explained in details through signal processing technique, followed by extensive review and discussion of various methods and trends in identifying and minimizing written-in and real-time RRO contributors in high capacity magnetic hard disk drives. Finally, the key patents that have emerged in this subject will be identified accordingly in the context of this paper.
Keywords: Actuator, control, hard disk drives, positional error signals, repeatable runout, servo, spindle motor, Magnetic Hard Disk, repeatable runout (RRO), multi-terabyte (TB)
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