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M.2 (NGFF) Connector Pinout & Keys Explained

A detailed look at the M.2 standard, its various module keys, and common pin assignments.

The M.2 standard, formerly known as Next Generation Form Factor (NGFF), is a versatile specification for internally mounted computer expansion cards. It was designed to replace the mSATA standard and is used for a wide variety of devices, including Wi-Fi, Bluetooth, WWAN (cellular), GPS, NFC, and most notably, Solid State Drives (SSDs).

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M.2 Module Keys and Sockets

M.2 modules feature notches (keys) that correspond to different socket types on the motherboard or host device. These keys prevent incorrect insertion and ensure compatibility. A single M.2 card can have one or more notches.

The keying is defined by which pins are "missing" or "notched out" on the 75-pin edge connector. Here are the most common keys and their typical applications:

Key A (Pins 8-15 Notched)

  • Primary Interfaces: PCIe x1 (or x2 with some configurations), USB 2.0. Also supports I2C, DisplayPort x4 (optional).
  • Common Applications: Wi-Fi, Bluetooth, WiGig (Wireless Gigabit), NFC (Near Field Communication).
  • Socket 1 PCIe x1 mapping: lane 0 uses PETp0/PETn0 on pins 35/37 and PERp0/PERn0 on pins 41/43. REFCLK0 is on 47/49, PERST0# on 52, CLKREQ0# on 53, and PEWAKE0# on 55.
  • Often combined with Key E (see Key A+E).

Key B (Pins 12-19 Notched)

  • Primary Interfaces: PCIe x2, SATA, USB 2.0/3.0, Audio, UIM (SIM card), I2C, SMBus.
  • Common Applications: SSDs (SATA or PCIe x2 NVMe), WWAN (3G/4G/5G cellular modems), GPS.
  • Modules can be 22mm wide and various lengths (e.g., 2230, 2242, 2260, 2280, 22110).

Key E (Pins 24-31 Notched)

  • Primary Interfaces: PCIe x1 (or x2), USB 2.0. Also supports I2C, SDIO, UART, PCM.
  • Common Applications: Wi-Fi, Bluetooth, WiGig. Similar to Key A.
  • Socket 1 PCIe x1 mapping: lane 0 uses PETp0/PETn0 on pins 35/37 and PERp0/PERn0 on pins 41/43. REFCLK0 is on 47/49, PERST0# on 52, CLKREQ0# on 53, and PEWAKE0# on 55.
  • Often found in an A+E keyed slot for Wi-Fi cards.

Key M (Pins 59-66 Notched)

  • Primary Interfaces: PCIe x4 (main interface for high-performance NVMe SSDs), SATA (optional, depending on host support).
  • Common Applications: High-performance NVMe SSDs.
  • Modules can be 22mm wide and various lengths.

Combined Keys (e.g., B+M, A+E)

Some M.2 cards and slots use a combination of keys to support broader compatibility or multiple interfaces:

  • Key B+M: These cards have two notches (one for Key B, one for Key M). They are typically designed for SSDs and can be inserted into sockets keyed for B, M, or B+M. They usually support SATA and/or PCIe x2 NVMe protocols. The host socket determines which protocol is used.
  • Key A+E: Commonly used for Wi-Fi and Bluetooth combo cards. These cards can fit in sockets keyed for A or E. For the common Socket 1 PCIe x1 link, lane 0 uses PETp0/PETn0 on 35/37 and PERp0/PERn0 on 41/43, with REFCLK0 on 47/49, PERST0# on 52, CLKREQ0# on 53, and PEWAKE0# on 55.

Important Note: Physical keying only prevents incorrect insertion. Electrical compatibility also depends on the host system supporting the protocol used by the M.2 card (e.g., a Key M slot might physically accept a SATA M.2 SSD with B+M keying, but if the slot only provides PCIe lanes, the SATA SSD won't work).

M.2 Form Factors & Mechanics

M.2 module sizes are commonly expressed as a four- or five-digit code in the form WWLL (e.g., 2280), where WW is the width in millimeters and LL is the length in millimeters. The most common width in PCs is 22 mm; length varies by application and chassis.

Common Sizes (WWLL)

  • 2230 → 22 × 30 mm — Very compact; Wi‑Fi/BT, WWAN, embedded.
  • 2242 → 22 × 42 mm — Compact SSDs or small form‑factor systems.
  • 2260 → 22 × 60 mm — Less common; some OEM platforms.
  • 2280 → 22 × 80 mm — Most consumer SSDs in desktops/laptops.
  • 22110 → 22 × 110 mm — Workstation/server or high‑capacity SSDs.
22 mm 80 mm (example length) 2230 2242 2260 2280 22110
Illustrative only. Standoff positions vary by board; consult your vendor documentation.

Thickness & Component Sides

  • Boards may be single‑sided (components on one face) or double‑sided. Chassis clearance and heatspreaders can limit supported module types.
  • Exact mechanical envelopes and tolerances are defined by the official specification; always verify your system’s supported thickness.

Sockets (1/2/3) and Typical Uses

  • Socket 1 — Typically wireless (Wi‑Fi/Bluetooth), often Key A/E.
  • Socket 2 — WWAN or SSD (SATA/PCIe x2) on some designs.
  • Socket 3 — Storage (NVMe PCIe or SATA), commonly Key M or B+M.

Mounting & Hardware

  • Modules fasten via a single mounting hole at the free end. Motherboards provide standoff positions at common lengths (2230/2242/2260/2280/22110).
  • Consumer boards typically use a small M2 screw with a standoff; don’t overtighten. Use the standoff location matching the module length.

Thermal Considerations

  • High‑performance NVMe SSDs can throttle thermally. Heatsinks or pads are commonly recommended by vendors and motherboard makers.
  • Ensure airflow and avoid obstructing thermal pads/heatsinks with cables.

RF Considerations (Wi‑Fi/WWAN)

  • Wireless modules may require external antennas via miniature RF connectors (e.g., MHF4/u.FL). Confirm connector type and cable routing.

Reading Module Labels

  • Size code (e.g., 2280) → width × length in mm.
  • Keying and interface (e.g., “Key M, PCIe Gen3×4 NVMe” vs “SATA”) determine compatibility and performance; match to the host slot’s capabilities.

For exact dimensions, tolerances, and keep‑out zones, consult the official specification and your motherboard/device vendor documentation.

M.2 Connector Pinout (75 Positions)

The M.2 connector has 75 positions, but there is no single universal per-pin function table that applies equally to Key A, Key E, Key B, and Key M. The same physical pin number can carry different signals depending on whether the slot is Socket 1, Socket 2, or Socket 3.

The safest way to read M.2 pinouts is by socket family. The reference blocks below group the most important pins by the socket definitions used in practice for wireless modules, WWAN/storage modules, and NVMe SSDs.

Socket 1: Key E And Common A+E Wireless Modules

Typical Wi-Fi / Bluetooth lane-0 mapping used by connectivity cards.

Signal Group Pins Notes
Power / Ground3.3V: 2, 4, 72, 74. GND: 1, 7, 18, 33, 39, 45, 51, 57, 63, 69, 75Common Socket 1 rails.
USB 2.03 / 5Bluetooth usually rides on USB2.
PCIe Lane 0 Tx35 / 37PETp0 / PETn0.
PCIe Lane 0 Rx41 / 43PERp0 / PERn0.
PCIe REFCLK047 / 49REFCLKp0 / REFCLKn0.
PCIe Sideband52 / 53 / 55PERST0#, CLKREQ0#, PEWAKE0#.
Wireless Disable54 / 56W_DISABLE2# and W_DISABLE1#.
Key E extras8-23, 32, 34, 36, 58, 60, 62SDIO, UART, PCM/I2S, I2C/ALERT and coexistence signals.
Dual A+E extras44, 46, 48, 58, 60, 62, 66, 68, 70COEX, SMBus-style sidebands, and UIM-related pins on common combo modules.

Mechanical Key A Is Not The Same Low-Pin Map As Key E

Mechanical Key A keeps USB2 on pins 3/5 and PCIe lane 0 on 35/37/41/43, but many pins that Key E uses for SDIO/UART/PCM are repurposed for DisplayPort or WiGig-style signaling. In the Socket 1 Key A mapping, pins 17-34 carry DisplayPort and related sidebands, while the optional second PCIe lane lives on 59/61 and 65/67 with sidebands on 66/68/70/71/73.

Socket 2: Key B And The Shared B+M Storage Subset

Used by WWAN modules and by SATA / PCIe x2 storage designs.

Signal Group Pins Notes
USB 2.07 / 9Key B WWAN base interface.
PCIe / SATA Lane 0 Tx47 / 49PETn0 / PETp0, shared with SATA A- / A+.
PCIe / SATA Lane 0 Rx41 / 43PERn0 / PERp0, shared with SATA B+ / B-.
Optional Lane 129 / 31 / 35 / 37PCIe lane 1, often multiplexed with USB 3.x or SSIC depending on the host configuration.
PCIe Sideband50 / 52 / 53 / 54 / 55PERST#, CLKREQ#, REFCLKn, PEWAKE#, REFCLKp.
Storage Sideband38DEVSLP.
UIM / SIM30, 32, 34, 36, 66UIM_RESET, UIM_CLK, UIM_DATA, UIM_PWR, SIM_DETECT.
Configuration Detect1, 21, 69, 75Used by the host to identify the intended Key B module interface.
B+M note12-19 and 59-66 removedB+M SSDs usually expose the shared storage subset of Socket 2, not a separate canonical socket definition.

Socket 3: Key M NVMe / SATA Storage

Main storage socket for NVMe SSDs, with optional SATA support depending on the host.

Signal Group Pins Notes
PCIe / SATA Lane 041 / 43 / 47 / 49PERn0, PERp0, PETn0, PETp0. Shared with SATA B+/B- and A-/A+.
PCIe Lane 129 / 31 / 35 / 37PERn1, PERp1, PETn1, PETp1.
PCIe Lane 217 / 19 / 23 / 25PERn2, PERp2, PETn2, PETp2.
PCIe Lane 35 / 7 / 11 / 13PERn3, PERp3, PETn3, PETp3.
PCIe Sideband50 / 52 / 53 / 54 / 55PERST#, CLKREQ#, REFCLKn, PEWAKE#, REFCLKp.
SMBus / Alert40 / 42 / 44SMB_CLK, SMB_DATA, ALERT#.
Other Sideband38 / 68 / 69DEVSLP, SUSCLK, and PEDET.

These reference blocks were aligned against Socket 1 / Key E, Socket 2 / Key B, Socket 3 / Key M, and the common dual A+E module references. Always verify the exact host wiring and module datasheet before routing a board or buying an adapter.

Configuration Pins (CONFIG_0-CONFIG_4)

Pins CONFIG_0, CONFIG_1, CONFIG_2, CONFIG_3, and CONFIG_4 are used by the M.2 module to indicate its presence and supported functionalities to the host system. The host reads the state of these pins (grounded by the module or left open) to determine how to interface with the card. The exact interpretation varies by module type (SSD, WWAN, Wi-Fi).

References & Further Reading

Need a Specific M.2 Pinout?

While this page provides a general overview, our M.2 Pinout Generator tool will help you find pinouts tailored to specific applications and keys!

M.2 Pinout Generator

This page provides a general overview. Always consult the official datasheets for your specific M.2 card and host device for precise pinout information and compatibility. Pin functionalities can vary significantly based on the device and its intended application.

FAQ - M.2 (NGFF) Pinout

What is the M.2 (NGFF) pinout used for?
The M.2 pinout maps PCIe, SATA and USB2.0 signals to the edge connector. The exact lanes and sidebands depend on the key (B, M, E) and the host wiring.
B-key vs M-key: what are the electrical differences?
B-key typically offers PCIe x2 and/or SATA plus USB2.0; M-key supports PCIe x4 for NVMe SSDs. Notch position prevents cross-insertion and the lane count differs.
Where are the USB 2.0 pins on M.2?
USB D+ and D- are present on specific pins for B/E keys so wireless or WWAN modules can enumerate even without PCIe. Many M-key NVMe slots omit USB wiring.
Does a SATA M.2 drive work in an NVMe-only M-key slot?
No. NVMe requires PCIe lanes. A motherboard must route SATA to the socket for a SATA M.2 SSD to work. Check the board manual for SATA vs PCIe support.
What does E-key expose for Wi-Fi/BT modules?
E-key usually exposes PCIe x1 and USB2.0, sometimes SDIO/UART depending on the host. RF control lines and CLKREQ#/PERST# sidebands follow the M.2 spec.
Which sideband signals are mandatory (CLKREQ#, PERST#, PEDET)?
PERST# and CLKREQ# are commonly required for PCIe power-management. Presence detect (PEDET) and REFCLK routing depend on platform design choices.
How to identify the key from the board only?
Check notch position and silkscreen. If the manual states 'PCIe x4/NVMe', it is M-key; 'PCIe x2/SATA/USB' typically indicates B-key; WLAN sockets are often E-key.

See Also