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Studio render of a motherboard with an M.2 SSD in its slot and a 2.5-inch drive connected by a flat SATA cable, both leading to a controller chip

Topic · 2 min read

Storage interfaces and controllers

Storage interfaces define how a host expresses commands and receives results. The protocol, controller, physical packaging, and persistent medium are related but separate properties of a storage device.

The bigger picture

A controller translates requests into operations the medium can perform and reports completion through a supported host interface. Modern paths can manage several outstanding operations rather than handling every request as one synchronous action. The operating system's software stack coordinates queues, buffers, and errors around that interface. Transport capabilities and the behavior of the storage medium should therefore be compared separately.

A device can also sit behind a bridge that changes the host-facing connection. The enclosure's transport then becomes another part of the capability and performance story. Read the following references as descriptions of interfaces, not as instructions to change a boot controller's mode. Such changes can affect whether an existing operating-system installation starts and belong in exact model-specific documentation.

Reading map: Storage interfaces and controllersFirst 1 topics in reading order: The bigger picture. Each topic links to its section or page.INSIDE THIS PAGEStorage interfaces and controllers1The bigger picture2 paragraphs

Storage

Note these before you change anything

Useful facts to have to hand while reading about storage interfaces and controllers.

  • A current backup before any change
  • Controller mode in firmware: AHCI, RAID or NVMe
  • Storage controller driver name and version
  • Drive health shown by the maker's own diagnostics

Storage: Reading and writing data

  1. File systemfiles and folders
  2. Storage stackvolumes and partitions
  3. Controller driverNVMe, AHCI or RAID
  4. Controlleron the board or a card
  5. DriveSSD or HDD
Conceptual schematic of a selected path, not every request. Shown in one direction; the reverse direction uses related layers. Real systems add services, filter drivers and firmware not shown. Highlighted: the layer a driver change affects.

Pages in Storage interfaces and controllers

Thumbnail for NVMe and command queues: a slim M.2 NVMe SSD with many short parallel, set beside a motherboard with an M.2 SSD in (Storage interfaces and controllers)Reference · 2 min read

NVMe and command queues

NVMe is a host interface and command set designed for nonvolatile memory devices. It defines how work is submitted and completed; it is not simply a synonym…

Thumbnail for SATA and the AHCI interface: a 2.5-inch SATA drive connected by an L-shaped data, set beside a motherboard with an M.2 SSD in (Storage interfaces and controllers)Reference · 2 min read

SATA and the AHCI interface

SATA describes a storage connection and protocol family, while AHCI defines a common programming interface for compatible host controllers. The two names…

Thumbnail for Storage bridges inside enclosures: a cutaway aluminium external enclosure showing a drive inside, set beside a motherboard with an M.2 SSD in (Storage interfaces and controllers)Reference · 2 min read

Storage bridges inside enclosures

An external enclosure can contain a bridge that translates between the computer-facing transport and the storage device inside. The bridge is an active part…

Thumbnail for Storage queue depth and workloads: an SSD in front of three rows of machined, set beside a motherboard with an M.2 SSD in (Storage interfaces and controllers)Reference · 2 min read

Storage queue depth and workloads

Queue depth describes how many storage operations can be outstanding within a particular part of a path. It is a workload and scheduling concept, not a…

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