 An M.2 2280solid-state drive (SSD), 22 mm wide and 80 mm long with the key in the M position | |
| Connects to | Motherboard via one of: |
|---|---|
| Common manufacturers | |
| Design firm | PCI-SIG |
| Introduced | November 1, 2013; 12 years ago (2013-11-01) |
| Dimensions |
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M.2 (pronounced "em-dot-too"),[1] formerly known as theNext Generation Form Factor (NGFF), is a specification for internally mounted computerexpansion cards and connectors. It was developed to replace the older Mini SATA (mSATA) and Mini PCIe (mPCIe) standards.
M.2 supports a variety of module sizes and interface types, offering greater flexibility for modern devices. It is widely used in compact systems such asultrabooks andtablet computers, particularly forsolid-state drives (SSDs), due to its smaller size and higher performance compared to mSATA.[2][3][4]
The M.2 connector can provide multiple interface options, including up to four lanes ofPCI Express, as well asSerial ATA 3.0 andUSB 3.0. The supported interfaces vary depending on the device and host implementation. M.2 modules and slots use different "keying" notches to indicate supported interfaces and to prevent incompatible installations.[2][3][5]
For storage devices, M.2 supports both the olderAdvanced Host Controller Interface (AHCI) and the newerNVM Express (NVMe) protocols. AHCI provides compatibility with legacy SATA-based systems and operating systems, while NVMe is designed for high-speed SSDs and allows for much faster performance by supporting multiple simultaneousI/O operations.[2]: 14 [6]
M.2 modules can integrate multiple functions, including the following device classes:Wi-Fi,Bluetooth,satellite navigation,near-field communication (NFC),digital radio,WiGig,wireless WAN (WWAN), andsolid-state drives (SSDs).[7] TheSATA revision 3.2 specification, in its gold revision as of August 2013[update], standardizes M.2 as a new format for storage devices and specifies its hardware layout.[2]: 12 [8]Buses exposed through the M.2 connector includePCI Express (PCIe) 3.0 and newer,Serial ATA (SATA) 3.0 andUSB 3.0; all these standards arebackward compatible.
The M.2 specification provides up to fourPCI Express lanes and one logicalSATA 3.0 (6 Gbit/s) port, and exposes them through the same connector so both PCI Express and SATA storage devices may exist in the form of M.2 modules. Exposed PCI Express lanes provide a pure PCI Express connection between the host and storage device, with no additional layers ofbus abstraction.[9]PCI-SIG M.2 specification, in its revision 1.0 as of December 2013[update], provides detailed M.2 specifications.[2]: 12 [10]
Three options are available for the logical device interfaces and command sets used for interfacing with M.2 storage devices, which may be used depending on the type of M.2 storage device and availableoperating system support:[2]: 14 [6][9]
The M.2 standard is based on themSATA standard, which uses the existingPCI Express Mini Card (Mini PCIe)form factor and connector. M.2 adds the possibility of largerprinted circuit boards (PCBs), allowing longer modules and double-sided component population. Consequently, M.2SSD modules can provide double the storage capacity within the footprint of an mSATA device.[2]: 20, 22–23 [4][13]
M.2 modules are rectangular, with anedge connector on one side and a semicircular mounting hole at the center of the opposite edge. The edge connector has 75 positions with up to 67 pins, employing a 0.5 mmpitch and offsetting the pins on opposing sides of the PCB from each other. Each pin on the connector is rated for up to 50 V and 0.5 A, while the connector itself is specified to endure 60 mating cycles.[14]: 6 However, many M.2 slots (Socket 1, 2 and 3) found on motherboards only provide up to 3.3V power.[15][16][17]
The M.2 standard allows module widths of 12, 16, 22 and 30 mm, and lengths of 16, 26, 30, 38, 42, 60, 80 and 110 mm. Initial line-up of the commercially available M.2 expansion cards is 22 mm wide, with varying lengths of 30, 42, 60, 80 and 110 mm.[3][5][14][18] The codes for the M.2 module sizes contain both the width and length of a particular module; for example, "2242" as a module code means that the module is 22 mm wide and 42 mm long, while "2280" denotes a module 22 mm wide and 80 mm long.
An M.2 module is installed into a mating connector provided by the host's circuit board, and a single mounting screw secures the module into place. Components may be mounted on either side of the module, with the actual module type limiting how thick the components can be; the maximum allowable thickness of components is 1.5 mm per side, and the thickness of the PCB is0.8 mm ± 10%.[10] Different host-side connectors are used for single- and double-sided M.2 modules, providing different amounts of space between the M.2 expansion card and the host's PCB.[4][5][14] Circuit boards on the hosts are usually designed to accept multiple lengths of M.2 modules, which means that the sockets capable of accepting longer M.2 modules usually also accept shorter ones by providing different positions for the mounting screw.[19][20]
| Key ID | Notched pins | Provided interfaces | Dimensions | Uses |
|---|---|---|---|---|
| A (Socket 1) | 8–15 | 2 × PCIe ×1, USB 2.0,I2C andDP ×4 | 1630, 2230, 3030 | Wi-Fi,WWAN,GPS,Bluetooth,NFC |
| B (Socket 2) | 12–19 | SATA, PCIe ×2, USB 2.0 and 3.0, audio,UIM,HSIC,SSIC, I2C andSMBus | 2230, 2242, 2260, 2280, 22110 | SSD |
| C | 16–23 | Reserved for future use | ||
| D | 20–27 | |||
| E (Socket 1) | 24–31 | 2 × PCIe ×1, USB 2.0,I2C,SDIO,UART,PCM andCNVi | 1630, 2230, 3030 | Wi-Fi,WWAN,GPS,Bluetooth,NFC |
| A+E (Socket 1) | 8–15 and 24–31 | 2 × PCIe ×1, USB 2.0 andCNVi | 1630, 2230, 3030 | Wi-Fi,WWAN,GPS,Bluetooth,NFC |
| F | 28–35 | Future Memory Interface (FMI) | ||
| G | 39–46 | Reserved for custom use (unused in the M.2 specification) | ||
| H | 43–50 | Reserved for future use | ||
| J | 47–54 | |||
| K | 51–58 | |||
| L | 55–62 | |||
| M (Socket 3) | 59–66 | SATA, PCIe ×4, and SMBus | 2230, 2242, 2260, 2280, 22110 | SSD |
| B+M (Socket 2) | 12–19 and 59–66 | SATA, PCIe ×2, and SMBus | 2230, 2242, 2260, 2280, 22110 | SSD |
| Type ID | Top side | Bottom side |
|---|---|---|
| S1 | 1.20 mm | N/a |
| S2 | 1.35 mm | N/a |
| S3 | 1.50 mm | N/a |
| D1 | 1.20 mm | 1.35 mm |
| D2 | 1.35 mm | 1.35 mm |
| D3 | 1.50 mm | 1.35 mm |
| D4 | 1.50 mm | 0.70 mm |
| D5 | 1.50 mm | 1.50 mm |
The PCB of an M.2 module provides a 75-position edge connector; depending on the type of module, certain pin positions are removed to present one or more keying notches. Host-side M.2 connectors (sockets) may populate one or more mating key positions, determining the type of modules accepted by the host; as of April 2014[update], host-side connectors are available with only one mating key position populated (either B or M).[5][14][11] Furthermore, M.2 sockets keyed for SATA or two PCI Express lanes (PCIe ×2) are referred to as "socket 2 configuration" or "socket 2", while the sockets keyed for four PCI Express lanes (PCIe ×4) are referred to as "socket 3 configuration" or "socket 3".[2]: 15 [24]
For example, M.2 modules with two notches in B and M positions use up to two PCI Express lanes and provide broader compatibility at the same time, while the M.2 modules with only one notch in the M position use up to four PCI Express lanes; both examples may also provide SATA storage devices. Similar keying applies to M.2 modules that utilize provided USB 3.0 connectivity.[5][11][25]
Various types of M.2 modules are denoted using the "WWLL-HH-K-K" or "WWLL-HH-K" naming schemes, in which "WW" and "LL" specify the module width and length in millimeters, respectively. The "HH" part specifies, in an encoded form, whether a module is single- or double-sided, and the maximum allowed thickness of mounted components; possible values are listed in the right table above. Module keying is specified by the "K-K" part, in an encoded form using the key IDs from the left table above; it can also be specified as "K" only, if a module has only one keying notch.[5][14]
Beside socketed modules, the M.2 standard also includes the option for having permanentlysoldered single-sided modules.[14]
In 2017, Samsung introduced a new form factor calledNext Generation Small Form Factor (NGSFF), also known as NF1 or M.3, which may replaceU.2 in server applications.[26] The NGSFF connector is electrically and dimensionally compatible with M.2 (revision 1.1)'s connector; new functionality is achieved through previously unused (N/C) pins.[27] The main changes compared to M.2 are:
In 2018, the PCI-SIG issued a warning that NGSFF's new pin usage clashes with the pin usage in the upcoming 1.2 revision of the M.2 standard. The new revision uses some of the previously non-connected (N/C) pins to deliver 1.8 V power and USB 2.0 data on the "M" socket. Samsung has sought to standardize its NGSFF/NF1 throughJEDEC, but the process appears to have stalled.[29]
JEDEC JESD233 is another specification calledCrossover Flash Memory (XFM) for XFM Embedded and Removable Memory Devices (XFMD). It targets to replace the M.2 form factor with a significantly smaller one (also called XT2), so that it can also be designed as an alternative to soldered memory. XFM Express utilizes aNVMe logical interface over aPCI Express physical interface.[30][31]
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