{
  "slug": "command-descriptor-block",
  "term": "Command descriptor block (CDB)",
  "aliases": [
    "CDB",
    "SCSI CDB"
  ],
  "definition": "A command descriptor block (CDB) is the byte-encoded description of a SCSI command.",
  "note": "Command and data: The CDB identifies a command and is distinct from its associated data payload. Common fixed-length formats are 6, 10, 12 and 16 bytes; the operation and command set determine the layout. [snia-cdb] [linux-guide]\n\nInterpretation: Decode the command using the applicable device command set, such as SBC for block devices or SSC for sequential-access devices. A shared SCSI transport does not make their operations interchangeable. [t10-architecture]",
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "related": [
    "scsi",
    "initiator-target",
    "logical-unit-number",
    "scsi-check-condition"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "snia-cdb",
      "title": "SNIA dictionary: Command Descriptor Block",
      "url": "https://www.snia.org/education/online-dictionary/term/command-descriptor-block",
      "accessed": "2026-10-20"
    },
    {
      "id": "linux-guide",
      "title": "Linux SCSI Interfaces Guide: protocol versus bus and subsystem layers",
      "url": "https://docs.kernel.org/driver-api/scsi.html",
      "accessed": "2026-10-20"
    },
    {
      "id": "t10-architecture",
      "title": "T10: SCSI standards architecture and command families",
      "url": "https://www.t10.org/drafts.htm",
      "accessed": "2026-10-20"
    }
  ],
  "provenance": [
    "The listed fixed lengths are examples, not an exhaustive limit on SCSI command formats."
  ],
  "updated": "2026-10-20"
}