# 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.

<figure><img src="https://620581463-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FNrxMTPBjxxzJFosGtQvH%2Fuploads%2FBvk341kA2EiAHcYRcWcm%2Fa.png?alt=media&#x26;token=990049f2-2dc9-47af-8a63-f31e152559c5" alt=""><figcaption></figcaption></figure>

## Peripheral Component Interconnect Express (PCIe) BUS

PCIe is a high-speed serial transfer interface standard.

M.2 connector supports up to four PCIe channels.

<figure><img src="https://620581463-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FNrxMTPBjxxzJFosGtQvH%2Fuploads%2F2iRAMOeLqrYBP2iEk47e%2Fa.png?alt=media&#x26;token=a9063199-32e7-4122-9f2e-07e4dd7cae8a" alt=""><figcaption><p>Evolution of PCIe</p></figcaption></figure>

## Apple SSD Proprietary Connectors

<figure><img src="https://620581463-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FNrxMTPBjxxzJFosGtQvH%2Fuploads%2F2rJzivVnxhluqNLhUbqR%2Fa.png?alt=media&#x26;token=7cc45008-733f-45dd-b710-a657e92b96ea" alt=""><figcaption></figcaption></figure>

<figure><img src="https://620581463-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FNrxMTPBjxxzJFosGtQvH%2Fuploads%2Fp725LZSiew50Lk80zd33%2Fa.png?alt=media&#x26;token=9ff57df8-47d8-495a-8c96-33e761810912" alt=""><figcaption></figcaption></figure>
