{
  "slug": "embedded-servo",
  "term": "Embedded servo",
  "aliases": [
    "sector servo",
    "wedge servo"
  ],
  "definition": "Embedded servo interleaves prerecorded head-positioning information with user-data regions on an HDD recording surface.",
  "note": "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. [servo-manual]\n\nA 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. [servo-patent] [servo-manual]\n\nThe 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. [servo-honda]",
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-25",
  "related": [
    "hdd",
    "seek-time",
    "rotational-vibration",
    "position-error-signal"
  ],
  "citations": [
    {
      "id": "servo-manual",
      "title": "Maxtor: DiamondMax VL 30 Product Manual (2000), glossary GL-2 and GL-5",
      "url": "https://www.seagate.com/staticfiles/maxtor/en_us/documentation/manuals/dm_30vl_ultra_ata66_manual.pdf",
      "accessed": "2026-10-25"
    },
    {
      "id": "servo-patent",
      "title": "Ali / Seagate: Servo wedge skipping during track seeking, US10706882B1 (2020), Figs. 2-4",
      "url": "https://patents.google.com/patent/US10706882B1",
      "accessed": "2026-10-25"
    },
    {
      "id": "servo-honda",
      "title": "Honda: Temperature Dependent Robust Control of Hard Disk Drives (2016), sections 2.2-2.4",
      "url": "https://dept.aem.umn.edu/~SeilerControl/Thesis/2016/Honda_16PhD_TemperatureDependentRobustControlOfHDDs.pdf",
      "accessed": "2026-10-25"
    },
    {
      "id": "mechanics",
      "title": "Hesela: HDD mechanical faults, evidence and diagnostic limits",
      "url": "https://hesela.com/analyses/hdd-mechanical-failure-points/#servo-positioning",
      "accessed": "2026-10-25"
    }
  ],
  "provenance": [
    "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."
  ]
}