IntroductionHigh areal density recording requires advancement in both linear density and track density. In order to resolve the side-writing issue and the edge noise reading issue associated with high track density, discrete track recording (DTR) technology was proposed by some researchers recently [1], [2]. While the DTR technology offers many advantages, there are difficulties yet to be overcome. With the DTR media configuration proposed by Wachenschwanz, et al. [1], slider flyability becomes more challenging due to the land-groove structure. In addition, the discrete nature of the DTR makes the magnetic write width (MWW) narrower than its continuous counterpart (continuous track recording, CTR), resulting in lower signal amplitude. Therefore, it is the objective of this paper to evaluate the performance of DTR technology. Both tribological performance and electric performance were evaluated. Flyability and Tribology The DTR media were manufactured by an etching process at substrate level, and the magnetic layer was sputtered on the entire surface, including the lands and the grooves. Therefore, the groove needs to be deep enough to be effective (>20 nm). While the head/media clearance is measured from the slider body to the top surface of DTR media, the slider flying characteristics is a function of the distance from slider body to DTR disk's "mean plane". As a result, DTR sliders have softer air bearings, therefore, worse flying height tolerance and sensitivities to most parameters. In order to compensate for this shortcoming, implementation of dynamic fly height control (DFH) is necessary. In this project, air bearing was designed based on the mean plane flying height. The head/media clearance was verified by measuring the contact RPM at sea level, and the contact altitude at constant RPM. Magnetic Model and Parametric Test A custom-built recording system model was applied in this study. The model calculates the signal amplitude through the convolution of reader sensitivity and written track magnetization profiles. Magnetic and electronic noises were separately obtained by solving the well established analytical equations. When combined with the drive level track mis-registration (TMR) distribution, the model is capable to predict both on-track and off-track signal-to-noise ratio (SNR) and bit error rate (BER) performance. Furthermore, adjacent track squeeze (ATS) and write-unsafe (WUS) events can be simulated with the model. As expected, the on-track SNR and BER of DTR are generally worse than CTR, due to its narrower effective magnetic writer width (MWW) and not-enough gain from erase band noise reduction. The best scenario is DTR equivalent to CTR at the optimized land/groove ratio and reader width. In this model, adjacent track's side reading is assumed to be equally influential for both DTR and CTR, and its value is determined by reader skirt width. Although the on-track performance is not as promising, the model does show that DTR has advantage in off-track performance, such as ATS
To meet the areal density growth (∼60% compound annual growth rate) challenge in the disk drive industry, track density (tracks per inch, TPI) has been increasing at ∼30% rate. As the track density increases, the size of the erase band, unless controlled, becomes a significant portion of the written track. In this work, special equipment was developed to study (i) the size of erase bands, (ii) the effect of pole trimming on erase band and hooks, (iii) the effect of disk anisotropy on erase bands and hooks, and (iv) the effect of hooks and erase bands at high TPI. We demonstrated servo pattern writing and reading capability (through the drive preamp and channel) on a spin stand level, showing that for properly trimmed pole heads, hook and erase band size becomes insignificant. With untrimmed pole heads, isotropic disks showed smaller hooks compared to oriented disks. From this work, we concluded that at higher TPI, erase bands must be scaled so that the servo Gray code signal-to-noise ratio is not unduly degraded.
N. Suhrahmuny".llck. M. Chue' (1) Western Digital Corporalim. SX63 Rue Ferrilri Sasi lohe. CA 92118. USA limoductionAs the recording industry has pushed towards higher areal densities, lhe MR sensor sensitivity has progressively increased with n concomilant decrease in the sensor size to suppoii higher SNR and TPI requirements. The.% changes have made the render sensitive I O noise phenomena and bwlinc popping (BLP) evenls 111. The observed effecl in all head instahilily cases is extra pulses. missing pulses and T A like events.The servo psllern in the drive usually benrs the hrunl o l the elkcis o f (he inslahiiily kcause il is the least r o b u l in terms d dealing with the instahilily effect.; and i d w due 10 the delayed rcliiriilion ar inslability cvcnis. So an clkcctive drivc dcsign and mmur:sluring slrnlcgy has Io cope with all forms of head iimlahility. In this paper we propose n method to characterize head isslabilitics and propox Ihc MC olGray Hanuning. Golay. and Rccd Solomon (RS) codcs IO dcal with Track ID errors in the servo sector during write and read operations. We tiral discuss the churucteriratinn method and then show sew" system perbrmance with different ECC coder. Chariiclcrizalion Mcl hodIn order to understand the nature of the instability events disk drives were characleiired. The characterinlion method accessed lhc d i k e in iiiltive Inode using lbe setup sliow~~ iii Figurrl. A random seek operation WI F performed to a drive data track and the Servo Gray Code (GCI data for that track were captured using an oxillowope. Scrvo GC values for a numher of sew" tracks were collected rimiliirly lhrough rilndoin wrilelreild aeeka. A wriwure prugram was lhen used Iu compaile the expected GC to the captured GC values and count the numher of errors and genet ate a histogmm. A typical histogram of lhc rcsults is shown in Figure 2. Details oflhe Error Correcting CodeAs Seen in Figure 2 most errors are single hit (missing and exlra bill errors. This suggests lhal 1hit and 2-hit error correcling code9 cm he used IO mitigate the effect of these errors on the l r x k ID decvding prwess. In lhis nule we consider Hitmming. Gul;iy and RS Cutler. These cudrs have k e n modified in order to mainlain Ihe gray properly or the Gray Code. This is done hy ensuring that adjiiccnt track id's arc mvppcd 10 codcd valucs in Ihc code domain that arc il minimum dktmce apan. When more Ihan n single codeword is used to rcpre3eilt adjacent track id's rhe firs1 aid second codewords arc inlapped in reverw order. The decoding ol t h e e codes iF done lhrougll
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