Browse Prior Art Database

Technique for Assessing the Need to Reformat a Head Disk Assembly

IP.com Disclosure Number: IPCOM000105583D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 75K

Publishing Venue

IBM

Related People

McCrery, CF: AUTHOR

Abstract

A Head Disk Assembly (HDA), when subjected to thermal shock and/or mechanical shock, have a tendency to take on a permanent off-track shift of the data head relative to the servo head. This means that when the servo head is precisely on-track, some data heads are off-track; i.e., the head is in a different position from where it was when the track was formatted initially, having shifted toward one of the adjacent tracks. If this shift becomes too great, it can cause data errors when reading data from the HDA; and, in extreme cases, the shift can cause a write on track N to partially erase data on track N+1 or N-1 (depending on the direction of the shift). Either case can cause loss of customer data.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Technique for Assessing the Need to Reformat a Head Disk Assembly

      A Head Disk Assembly (HDA), when subjected to thermal shock
and/or mechanical shock, have a tendency to take on a permanent
off-track shift of the data head relative to the servo head.  This
means that when the servo head is precisely on-track, some data heads
are off-track; i.e., the head is in a different position from where
it was when the track was formatted initially, having shifted toward
one of the adjacent tracks.  If this shift becomes too great, it can
cause data errors when reading data from the HDA; and, in extreme
cases, the shift can cause a write on track N to partially erase data
on track N+1 or N-1 (depending on the direction of the shift).
Either case can cause loss of customer data.  Hence, there may be a
need after significant thermal and/or mechanical shocks to either
test the HDA to determine whether the shift is within acceptable
bounds or to reformat the HDA so that all data tracks are once again
aligned with the servo tracks.  Since the reformat operation is
undesirable from a customer standpoint, a test which can determine
whether too much shift has occurred is of significant value.  This
disclosure describes a method for doing so.

TECHNICAL DESCRIPTION - Head shift can be resolved into two
components:  the "DC" shift, which remains constant during the
rotation of the spindle, and the "AC" shift, which varies
sinusoidally as the spindle rotates.  The measurement technique
described here detects whether the combined "DC" and "AC" shift ever
causes the error rate to exceed some specified limit, thus requiring
a reformat of the HDA.

      In order to measure "AC" shift, the peak error rate (occurring
at those points around the track where the shift is greatest) must be
measured.  This is done by guaranteeing that the error rate will be
measured accurately on a record that is wholly within the top 10% of
the amplitude of the sinusoidal "AC" shift curve.  Since the "DC"
shi...