Gapless Servo Sectors in Disk Drives
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Solution Overview
Problem
Conventional servo systems in disk drives consume a significant portion of the recording surface with write-to-read gaps, limiting the space available for user data and requiring complex hardware and firmware adaptations.
Innovation Solution
Eliminating the write-to-read gap in selected sectors, referred to as gapless SIDs, allows for additional space to be used for user data or servo information, such as RRO fields, while maintaining servo system functionality by using PES bursts for track-following and delaying servo gate control signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If write-to-read gap is included in all sectors, then servo system can reliably switch from writing to reading, but data format efficiency decreases and user data space is reduced
Solution Approach 1:
The patent divides servo sectors into two categories: full servo sectors that include the complete write-to-read gap, and gapless servo sectors that eliminate the gap. This segmentation allows different portions of the disk to have different gap configurations, enabling the system to achieve both reliability (through full servo sectors) and improved data efficiency (through gapless servo sectors).
Solution Approach 2:
The patent applies different gap configurations to different local regions (sectors) of the disk based on specific conditions. Gapless sectors are used when the servo system can reliably determine track position without the gap, while full servo sectors are used when additional switching time is needed. This local differentiation optimizes overall system performance.
2Productivity
If write-to-read gap is eliminated in selected sectors, then data format efficiency increases by 0.8 to 1.0%, but servo system must accurately determine track position without gap assistance
Solution Approach 1:
The patent uses PES (Position Error Signal) bursts to provide preliminary track position information before the actual write operation begins. This preliminary positioning data allows the servo system to accurately determine track position even in the absence of a write-to-read gap, enabling gapless sector operation while maintaining measurement precision.
3Productivity
If gapless sectors are used, then more space is available for user data, but complex hardware and firmware adaptations are required
Solution Approach 1:
The patent implements a dynamic sector format that can switch between full servo sector mode and gapless servo sector mode based on disk surface location and operational conditions. This dynamic adaptation allows the system to optimize for either reliability or data efficiency as needed, while the servo control firmware automatically manages the transitions without requiring complex hardware modifications.
Data Source
AI summary
Disk drives are described in which the conventional write-to-read gap is omitted in selected sectors which frees up space that can be used for other purposes including writing a higher number of bits in the user data area in the gapless selected sectors. Alternative embodiments can use the additional space for servo information such as a repeatable run out (RRO) field. Conventional servo sector SID formats can be used for both gapped and gapless SIDs, which means that during seeking and reading operations full SIDs can be read for every wedge. The tradeoff for being able to write data much closer to the gapless SIDs is that the servo system does not detect the SAM or read the TID in the gapless SIDs during write operations.