Magnetic Disk Drive Head Positioning Offset for Track Demagnetization
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Solution Overview
Problem
As magnetic disk drives increase in capacity, the narrow track pitch leads to demagnetization of adjacent tracks due to leakage magnetic fields, resulting in increased error rates and the need for frequent track refreshing, which decreases drive performance.
Innovation Solution
A magnetic disk drive with a write count memory and a read offset setting module that adjusts the head positioning by calculating an offset based on pre-stored erase widths to optimize the read position, reducing demagnetization and error rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If track refreshing is performed frequently to restore magnetization of adjacent tracks, then data reliability is improved, but drive performance deteriorates
Solution Approach 1:
The system performs preliminary actions by proactively adjusting the head reading position offset based on predicted erase width before significant demagnetization occurs. The controller calculates the offset by referencing stored erase width data corresponding to write counts, and positions the head accordingly during read operations. This preventive approach restores magnetization before it becomes critical, reducing the need for frequent track refreshing while maintaining data reliability.
2Productivity
If the threshold value for write count is set relatively high to reduce track refreshing frequency, then drive performance is improved, but error rate in reading tracks increases
Solution Approach 1:
The system dynamically adjusts the head reading position offset based on the current write count and corresponding erase width. Rather than using a fixed high threshold, the controller continuously adapts the offset parameter according to accumulated write operations. This dynamic adjustment allows the system to maintain optimal read positioning as demagnetization progresses, reducing error rates without requiring frequent track refreshing.
Solution Approach 2:
The system changes the parameter of head reading position offset based on write count and erase width data. The controller references stored erase width information corresponding to different write counts and adjusts the offset parameter accordingly. This parameter change allows the system to compensate for demagnetization effects progressively, maintaining data reliability while reducing the frequency of track refreshing operations.
3Ease of operation
If head positioning is performed at the center line of the target track, then positioning simplicity is improved, but demagnetization of adjacent tracks increases due to leakage magnetic field
Solution Approach 1:
The system introduces asymmetry in head positioning by deliberately offsetting the reading position from the center line of the target track. The controller calculates and applies an offset based on erase width data, positioning the head asymmetrically relative to the track center. This asymmetric positioning reduces the exposure of adjacent tracks to leakage magnetic fields during write operations, thereby reducing demagnetization while maintaining positioning through controlled offset adjustment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces read error rates and minimizes the need for track refreshing, maintaining drive performance by positioning the head at an optimal offset from the center line based on erase widths, thereby preventing data loss.
Implementation Method 1
a magnetic field generated by the head includes a component that makes no contribution to data writing
Implementation Method 2
data magnetically written in tracks adjacent to a target track might be magnetically degraded when data is magnetically written to the target track with a head (magnetic head)
Data Source
AI summary
According to one embodiment, a magnetic disk drive comprises a write count memory, a read offset setting module and a controller. The write count memory stores a write count for each track or for each zone on a disk. The read offset setting module sets, in accordance with a write count for an adjacent track to a target track or for a zone to which the adjacent track belongs, an offset from a predetermined position on the target track in a read position in which a head is to be positioned when the head is positioned on the target track for data read. The write count is stored in the write count memory. The controller positions the head in a position shifted from the predetermined position by the set offset.