embedded-servo · shipping · also sector servo, wedge servo

Embedded servo

Embedded servo interleaves prerecorded head-positioning information with user-data regions on an HDD recording surface.

The data head reads positioning patterns between data regions, allowing the controller to locate it relative to a track. This differs from reserving an entire recording surface for servo information. [1]

A servo wedge spans tracks; its intersection with an individual track contains a servo sector. Position information feeds the positioning controller, rather than serving as user-data error correction. [2] [1]

The associated position error signal helps the actuator follow the selected track as the disk rotates. Track following is an active feedback task, not a one-time seek followed by an immobile head. [3]

Relations

related
Hard disk drive (HDD), Seek time, Rotational vibration (RV), Position error signal (PES)

Citations

  1. Maxtor: DiamondMax VL 30 Product Manual (2000), glossary GL-2 and GL-5 (accessed 2026-10-25)
  2. Ali / Seagate: Servo wedge skipping during track seeking, US10706882B1 (2020), Figs. 2-4 (accessed 2026-10-25)
  3. Honda: Temperature Dependent Robust Control of Hard Disk Drives (2016), sections 2.2-2.4 (accessed 2026-10-25)

Further reading

  1. Hesela: HDD mechanical faults, evidence and diagnostic limits (accessed 2026-10-25)
Sources & caveats
  • The 2000 manual supplies architectural terminology, not current performance specifications. The 2020 patent illustrates a design; it does not establish adoption in every drive.
  • No universal servo-area fraction, wedge count, sampling rate or positioning precision is assigned.

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Hesela team. Embedded servo. Hesela. 2026-10-25. https://hesela.dev/terms/embedded-servo/