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Optimal Method of Increasing Life of Magnetoresistive Head in Sector Servo

IP.com Disclosure Number: IPCOM000122277D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Brown, DH: AUTHOR [+2]

Abstract

The magnetoresistive (MR) head has "power-on" time limitations due to the electromigration of the MR element. This invention allows MR heads to be used as servo transducers for files with lifetime operating hours hundreds of times greater than the safe power-on hours for an MR head.

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Optimal Method of Increasing Life of Magnetoresistive Head in Sector
Servo

      The magnetoresistive (MR) head has "power-on" time
limitations due to the electromigration of the MR element. This
invention allows MR heads to be used as servo transducers for files
with lifetime operating hours hundreds of times greater than the safe
power-on hours for an MR head.

      The MR head used on direct access storage devices (DASDs) is
comprised of two elements mounted on a single slider.  One element,
the MR stripe, is used to read the magnetic flux transitions recorded
on the disk surface.  The other, an inductive thin film head element,
is used to write the information on the disk during write operations.

      This invention uses the ability of the thin film write element
to read back servo pattern flux transitions when the DASD is idle.
Since idle time is a significant portion of the power-on hours of a
file, the life of the MR head can extend considerably by turning off
the bias current during these idle times.  The advertised lifetimes
of a low end DASD are 40,000 to 50,000 power-on hours.  The lifetime
of an MR head with 10 ma of bias current is on the order of
100 hours before electromigration begins to increase the failure rate
of the MR head to unacceptable levels.

      File idle time is that time where the file is not performing a
seek, read, or write operation.  At those times, the actuator is
merely in a holding pattern so that if a request to move to a track
comes in, the servo controller can determine which direction and how
fast to move toward the requested location.  Obviously, if the servo
readback were turned off by shutting down all of the MR heads, the
actuator would wander to a new location and disk speed variations
would make it impossible for the servo control circuitry to remain in
sync with the sector servo bursts on the track.  Therefore, even
during idle time, the servo circuitry must stay actively synchronized
to the disk servo patterns.

      This article overcomes the impracticality of hooking up
multiple inductive t...