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Median Selection of Position Error Signals in a Data Recording Disk File

IP.com Disclosure Number: IPCOM000039224D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Makansi, T: AUTHOR

Abstract

The sensing of the head position error signal (PES) in a data recording disk file is accomplished by magnetically reading a previously written pattern. The pattern is separated from the data by using disjoint areas of the magnetic surfaces. For example, in "dedicated" configurations, one surface of a disk in a stack of disks is devoted to PES information, leaving other surfaces for data. In "sectored" configurations, PES information and data occupy disjoint sectors, or wedges, within each disk surface. Defects of various sorts in the magnetic coating on the disk surfaces can cause inaccuracies in the PES, and hence disrupt the tracking servo, causing track misregistration (TMR).

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Median Selection of Position Error Signals in a Data Recording Disk File

The sensing of the head position error signal (PES) in a data recording disk file is accomplished by magnetically reading a previously written pattern. The pattern is separated from the data by using disjoint areas of the magnetic surfaces. For example, in "dedicated" configurations, one surface of a disk in a stack of disks is devoted to PES information, leaving other surfaces for data. In "sectored" configurations, PES information and data occupy disjoint sectors, or wedges, within each disk surface. Defects of various sorts in the magnetic coating on the disk surfaces can cause inaccuracies in the PES, and hence disrupt the tracking servo, causing track misregistration (TMR). The PES errors due to defects primarily impact the write-to-write TMR, or track squeeze, and these errors hence reduce the track density achievable by the head positioning system. In particular, differential amplitude-encoded PES patterns have high defect sensitivity. A technique for removing noise from the PES is simply to "ignore" PES samples that appear to be erroneous. For example, rather than average three PES samples, the middle value of the three PES samples is used. This is known as median selection. If one of the three samples is the result of a signal dropout due to a defect, then it is effectively ignored in the median selection, provided the other samples are normal. Hence, median selection is effective i...