Jongseung Park

Capacity Advantage of Array-Reader-Based Magnetic Recording (ARMR) for Next Generation Hard Disk Drives

This paper proposes an array-reader-based magnetic recording (ARMR) approach for enhancing recording capacity in hard disk drives (HDDs). The HDD industry is now at crossroads to choose a technology that will support continued increase in recording density, and the top contenders are bit patterned media recording (BPMR) and heat-assisted magnetic recording (HAMR) for near-term and 2-D magnetic recording for long-term. Deployment of BPMR and HAMR has been delayed due to the challenges in media and heads. We propose the ARMR approach as a viable technology that can deliver significant capacity by combining array-reader-based readback with modest changes in readback signal processing. Offtrack performance evaluation using waveforms captured at various squeeze levels show that ARMR offers about 30% enhancement in capacity for single-track detection with two or three read elements positioned at different cross-track positions in the track.

Intertrack Interference Cancellation for Shingled Magnetic Recording

The intertrack interference in squeezed tracks of a magnetic hard disk drive is investigated based on captured waveforms. Specifically, extracted intertrack interference impulses and statistics are presented as a function of track squeeze and read offset. The bit-error-rate improvement of intertrack interference cancellation is shown based on simulations with captured drive waveforms. Architecture and implementation aspects for hard disk drives with intertrack interference cancellation are described.

Signal Model for Shingled Magnetic Recording Based on Data Dependent Erase Band Analysis Under Track Squeeze

In this study, a new signal model for shingled magnetic recording (SMR) is developed based on the drive waveform analysis with squeezed side tracks. Shingled recording effects are modeled by the data dependent effective write width or erase band, and the readback signals are represented by the weighted sum of the individual target and side track signals without intertrack interference (ITI). The weights of the target and side track signals, denoted by the ITI coefficients, are estimated from the drive waveforms collected from the track squeeze tests. Near the track edge location, the ITI coefficients are reduced by the erase band and the data-independent electronic noise is effectively increased. In addition, the ITI coefficients also depend on the recorded data patterns due to such effect as track width broadening by low frequency data patterns. Cross-track ITI coefficient profiles are modeled by Gaussian read sensitivity and rectangular magnetization functions and applied for various SMR conditions. Two data sets of 50% and 44% bit transition rates are investigated to take into account data dependent erase band. Based on the proposed signal model, the cross-track bit error rate (BER) performance of the SMR are evaluated with the readback signals, synthesized for various read offsets. The results show that modulating the data bits to have fewer bit transitions may improve the on-track BER performance, while its off-track performance can be limited by the increased ITI due to the low frequency data patterns. In addition, BER performance of SMR can be improved by the ITI cancellation (ITIC) scheme.