Effect of Trackwidth and Linear Spacing on Stability and Noise in Longitudinal and Perpendicular Recording

Abstract

Results from spin-stand and MFM experiments showing the effect of demagnetizing fields for both perpendicular and longitudinal media are presented. Spin-stand experiments involved measurement of the current required to erase square wave recordings to half amplitude. While longitudinal media require smaller currents to erase higher density recordings, perpendicular media require higher currents. MFM studies indicate differences in the onset of the magnetization reversal. The reversal initiates near the transition in longitudinal media but further from the transition in perpendicular media. Experimental results showing an increase in transition jitter with decreasing trackwidths are also reported for both longitudinal and perpendicular media.

An Efficient Noise Generator for Validation of Channels Equalizers

“…Figure 3 gives the curves of 10 consecutive captured sets of filter coefficients from the same drive, plotted on top of each other. The abscissa is the index of the filter coefficients (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12), the ordinate is the value of the corresponding coefficient byte (P1-P12). A curve plotted in one color shows the 12 filter coefficient values of one example set, connected by straight lines.…”

“…By plotting the histograms of each filter coefficient from contiguous measurement sequences of a disk drive (Figure 4) we will observe that each individual coefficient attains only a few distinct values, and almost all their variability is preserved in their few least significant bits (bits [1,2]-bits [1][2][3][4]).…”

“…The noise sources and levels have been extensively studied in [3,4], their effects on the signal in the read channel have also been investigated in [5][6][7][8]. The resulting inherent randomness in the channel filter coefficients has been proposed for use for random number generators in [9], but the included randomness extraction algorithm is very inefficient.…”