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Encoding the Head and Sector Address with Redundancy in the Servo Field in a No-ID Disk Drive

IP.com Disclosure Number: IPCOM000117828D
Original Publication Date: 1996-Jun-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 69K

Publishing Venue

IBM

Related People

Dobbek, JJ: AUTHOR [+2]

Abstract

Prior art disk drives traditionally included an Identification ("ID") field in each data region of the disk. The ID field comprised the cylinder, head, and sector number or the actual customer Logical Block Address (LBA), providing high data integrity, but at great cost in terms of overhead.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 53% of the total text.

Encoding the Head and Sector Address with Redundancy in the Servo
Field in a No-ID Disk Drive

      Prior art disk drives traditionally included an Identification
("ID") field in each data region of the disk.  The ID field comprised
the cylinder, head, and sector number or the actual customer Logical
Block Address (LBA), providing high data integrity, but at great cost
in terms of overhead.

      The present invention reduces the overhead associated with
prior art No-ID (TM)* disk drives and ID disk drives, while providing
comparable data integrity.  These objectives are achieved by:  1)
reducing the number of bits required to store the sector number in
the servo track id field as in prior art No-ID disk drives by
additional redundant checkers for sector number; and 2) splitting
head information into separate track id fields, thus reducing
individual servo field contribution to overhead.

      More specifically, the servo sector number is designed to have
several levels of redundancy, as described below:
  1.  In order for a servo sample to be considered a "good" sample
both
       the servo window must be found and the redundancy built into
the
       grey code for the track id must be valid.  A servo window
found
       will trigger the servo interrupt.
  2.  The free running servo clock provides an accurate counter which
       is used to predict the location of the next servo window.
This
       is used to trigger a servo processor interrupt if a real servo
       window was not found on the track.
  3.  With every servo interrupt there is an internal servo window
       counter state machine which increments until the number of
servo
       windows is exhausted.  It then wraps to zero and checks to
       confirm that index was found in that sample.  If the sample
was
       found good and index was not found, an error...