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.
Apple SSD Proprietary Connectors
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