Processing of Ex-Situ Acquired Signals from Magnetic Disks

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The ubiquity and high performance of hard disk drives for nonvolatile digital data storage cannot be denied. As the magnetic recording industry continues to develop new techniques for increasing storage density and reducing cost per bit, diagnostic and forensic tools for characterizing and interpreting the magnetic patterns recorded onto disk drive media become increasingly important. Therefore, this dissertation presents developments to the uniquely suitable spin-stand-based method of imaging magnetization patterns on media extracted from commercial hard disk drives. The emphasis of the presented research is placed on the following three areas: microscopy enhancement techniques for longitudinal magnetic recording media, "drive-independent" characterization and reconstruction of disk data, and the exploration of spin-stand microscopy in the novel context of perpendicular magnetic recording.

First, it is known that, while the spin-stand microscopy technique offers high-speed and massive scale imaging capabilities, the images obtained are corrupted by distortion due to the non-local sensing or finite spatial resolution of the imaging sensor. Two techniques for mitigating this distortion, one based on characterizing the head by means of its linear response function, and a new method based on spatial Hilbert transforms, are described and demonstrated. Furthermore, a two-dimensional extension of the Hilbert transform in the context of magnetic recording is derived based on physical arguments and its application to spin-stand imaging is demonstrated. Second, although magnetic media imaging is interesting in its own right, an extension of this capability is the identification of commercial hard disk drive write channels and the subsequent reconstruction of the data written to the associated disks in a "drive-independent" manner on the spin-stand. For fundamental and practical reasons, a multilayered encoding process is performed on digital data before it is written to the disk; the presented work details the theoretical and experimental results obtained in characterizing and reversing these codes. Finally, because perpendicular recording technology has recently come on the market in consumer disk drives, the spin-stand microscopy technique is extended to imaging the media employing this new mode of recording. In particular, the novel aspects of perpendicular recording are discussed and their impact on spin-stand microscopy is demonstrated.