{
  "slug": "racetrack-position-error",
  "term": "Racetrack position error",
  "aliases": [
    "racetrack shift error",
    "domain-wall position error"
  ],
  "definition": "In a racetrack read-channel model, a position error is an incorrect shift that causes a fixed read head to skip or reread stored domains.",
  "note": "In the read-channel model of Chee et al., overshifting skips a domain and produces a deletion in the observed bit sequence. A failed shift rereads the same domain, producing a sticky insertion: a repetition, not an arbitrary extra bit. The stored domain is not erased by the modeled deletion. These are synchronization errors, not simply flipped bit values. [c1]\n\nMultiple heads do not automatically provide independent observations. Their errors are correlated through the shared shift and head spacing; adjacent heads can return the same ambiguous sequence within a long run. The paper's bounded-error correction guarantees depend on coding constraints and head spacing, not merely the presence of a second head. [c1]\n\nPhysical positioning error is broader: continuous displacement from the intended position need not produce a discrete read error. Ishibashi et al. studied a Pt/GdFeCo wire about 5 micrometers wide using Kerr microscopy. Figure 4C reports 1,000 trials for Gd concentration x = 30.5%: bit-center position variance grew approximately linearly with average shift-pulse count at 14 V and 20 V, but nonlinearly at 8 V. The number of pulses per shift operation was adjusted between amplitudes to keep the average bit size near 5 micrometers. The shift pulse width was 2 ns, with 10 ms between pulses in the protocol. These are not a bit-error rate or sustained throughput measurement. [c2]",
  "status": "research",
  "advantages": [],
  "limitations": [
    {
      "text": "The cited work is a coding model, not a measured device failure rate.",
      "citationIds": [
        "c1"
      ]
    }
  ],
  "related": [
    "racetrack-memory"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "c1",
      "title": "Y. M. Chee, H. M. Kiah, A. Vardy, V. K. Vu and E. Yaakobi: Coding for Racetrack Memories, arXiv:1701.06874v1 (2017), sections I-III",
      "url": "https://arxiv.org/abs/1701.06874v1",
      "accessed": "2026-10-27"
    },
    {
      "id": "c2",
      "title": "M. Ishibashi et al.: Decoding the magnetic bit positioning error in a ferrimagnetic racetrack (2024), Fig. 4C; DOI 10.1126/sciadv.adq0898",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC11498212/",
      "accessed": "2026-10-28"
    }
  ],
  "updated": "2026-10-28",
  "provenance": [
    "Full-text review of a theoretical read-channel model; no hardware measurement, raw-data reanalysis or independent code-theorem proof is claimed.",
    "c2: full-text Results, Fig. 4C and Discussion; laboratory spatial variance, not raw-data reanalysis or measured read-error probability. Dense nanoscale behavior is not established by the micrometer-scale experiment.",
    "The distinction between continuous displacement, discrete read-channel events and measured event probabilities is a source-based interpretation, not a fitted conversion model."
  ]
}