SSD Connectors, Interfaces, and Transfer Protocols

Connectors:

• layer 1 – physical interface to connect devices. Examples: M.2, RJ45, ...

Link interfaces:

• layer 2 – handles data encoding. Examples: PCIe and SATA.

Transport protocols:

• layer 3 – handles data communication. Examples: NVMe, AHCI, and IDE.

M.2 – One connector, several transport protocols:

• M.2 connector = SATA link interface + SATA transport protocol.

• M.2 connector = PCIe link interface + AHCI transport protocol.

• M.2 connector = PCIe link interface + NVMe transport protocol.

M.2 Connector Interface

M.2, formerly known as the Next Generation Form Factor (NGFF).

• specification for internally mounted computer expansion cards.

• replaces the mSATA standard.

• more flexible physical specifications make it more suitable to:

  • solid-state storage.

  • particularly for use in small devices such as ultrabooks or tablets.

• protocols:

  • link interface: PCI Express 3.0 (up to four lanes).

  • transport protocol: Non-Volatile Memory Express (NVMe) as the logical device interface for M.2 PCI Express SSDs.

    • NVMe is designed to fully utilize the capability of high-speed PCIe storage devices to perform many I/O operations in parallel.

  • Serial ATA 3.0 and USB 3.0 (a single logical port for both).

  • the manufacturer selects which interfaces are supported.

• The M.2 connector has different keying notches:

  • to denote various purposes and capabilities of M.2 hosts (SSD, WiFi, 4G modem, . . . ).

  • to prevent plugging into feature-incompatible host connectors.

Peripheral Component Interconnect Express (PCIe) BUS

PCIe is a high-speed serial transfer interface standard.

M.2 connector supports up to four PCIe channels.

Evolution of PCIe

Apple SSD Proprietary Connectors