M.2 (NGFF) Connector Pinout and Keying Explained

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, orangetooth, WWAN (cellular), GPS, NFC, and most notably, Solid State Drives (SSDs).

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:

[Image placeholder: Diagram of M.2 Key Notches (A, B, E, M etc.)]

Visual representation of different M.2 key notches would be beneficial here.

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, orangetooth, WiGig (Wireless Gigabit), NFC (Near Field Communication).
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, orangetooth, WiGig. Similar to Key A.
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 orangetooth combo cards. These cards can fit in sockets keyed for A or E.

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 Connector Pinout (75 Positions)

The M.2 connector has 75 positions, with pins on both the top and bottom edges. Pin numbering is from 1 to 75. Not all pins are used by all modules; the specific pins used depend on the module's keying and the interfaces it implements.

The following table provides a general overview. Refer to specific device or motherboard documentation for precise implementations. Signals are often differential pairs (e.g., PETp0/PETn0 for PCIe Transmit Pair 0).

Pin	Pin	Pin	Pin
1	CONFIG_3	2	3.3V
3	GND	4	3.3V
5	GND	6	W_DISABLE# (Module Disable)
7	GND (PCIe_REQ#)	8	UIM_PWR (Key A/E) / Notched (Key A)
9	GND	10	UIM_DATA (Key A/E) / Notched (Key A)
11	PERn0 (PCIe Rx-)	12	Notched (Key B) / UIM_CLK (Key A/E)
13	PERp0 (PCIe Rx+)	14	Notched (Key B) / UIM_RESET (Key A/E)
15	GND	16	Notched (Key B) / UIM_VPP (Key A/E)
17	GND	18	Notched (Key B) / GND
19	Reserved / Notched (Key B)	20	Notched (Key B) / USB_D-
21	CONFIG_0	22	Notched (Key B) / USB_D+
23	PERn1 (PCIe Rx-)	24	Notched (Key E) / 3.3V
25	PERp1 (PCIe Rx+)	26	Notched (Key E) / GND
27	GND	28	Notched (Key E) / I2C_SCL
29	GND	30	Notched (Key E) / I2C_SDA
31	PETn0 (PCIe Tx-)	32	Notched (Key E) / I2C_IRQ#
33	PETp0 (PCIe Tx+)	34	Notched (Key E) / GND
35	GND	36	USB_D- (Key B) / UART_RXD (Key E)
37	GND	38	USB_D+ (Key B) / UART_TXD (Key E)
39	SATA_DEVSLP / PCIe_CLKREQ# (SSD)	40	GND
41	SATA_B_P / PETn1 (PCIe Tx-)	42	SATA_B_N
43	SATA_A_P / PETp1 (PCIe Tx+)	44	SATA_A_N
45	GND	46	PCIe_WAKE# / LED1#
47	REFCLKp (PCIe Clock+)	48	GND
49	REFCLKn (PCIe Clock-)	50	PCIe_RESET#
51	GND	52	PERST# (PCIe Reset) / SMB_CLK
53	PERn2 (PCIe Rx-)	54	CLKREQ# / SMB_DATA
55	PERp2 (PCIe Rx+)	56	PEWAKE# / SMB_ALERT#
57	GND	58	GND (DisplayPort HPD)
59	Notched (Key M) / CONFIG_1	60	Notched (Key M) / GND
61	Notched (Key M) / PETn2 (PCIe Tx-)	62	Notched (Key M) / GND
63	Notched (Key M) / PETp2 (PCIe Tx+)	64	Notched (Key M) / GND
65	Notched (Key M) / PETn3 (PCIe Tx-)	66	Notched (Key M) / GND
67	GND / PETp3 (PCIe Tx+)	68	SUSCLK (32kHz)
69	CONFIG_2	70	3.3V
71	GND	72	3.3V
73	GND	74	3.3V
75	CONFIG_4 / GND

Note: Pin functions can vary depending on the specific M.2 module type and the host system's implementation. "Notched" indicates pins removed for a specific key.

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

Primary Source: M.2 (NGFF) Connector Pinout at PinoutGuide.com
PCI-SIG
Wikipedia: M.2 on Wikipedia

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.