An M.2 SSD is a solid-state drive (SSD) that conforms to a computer industry specification written for internally mounted storage expansion cards of a small form factor. The specification was originally known as the Next-Generation Form Factor (NGFF), but the "next generation" moniker was dropped in favor of the M.2 -- pronounced M-dot-2 -- designation.
M.2 SSDs are designed to enable high-performance storage in thin, power-constrained devices, such as ultrabook and tablet computers. They are generally smaller than mSATA SSDs, for which they are intended as an alternative.
The M.2 form-factor specification was defined by the PCI Special Interest Group (PCI-SIG) consortium of technology industry vendors and the Serial ATA (SATA) International Organization. M.2 is an interface specification that supports multiple protocols and applications such as Wi-Fi, Universal Serial Bus (USB), PCI Express (PCIe) and SATA. With its support for protocols such as USB and Wi-Fi, M.2-compliant products are not limited to solid-state drives. For example, a number of vendors offer Wi-Fi-Bluetooth combo cards in the M.2 form factor. Innodisk offers an AI accelerator card that uses the M.2 interface and was the first to introduce an M.2 graphics card.
SATA M.2 and SATA Express (SATAe) are described in the SATA v3.2 Specification.
M.2 SSD vs. mSATA
M.2 is commonly referred to as an mSATA replacement, but mSATA SSDs still exist and will probably continue for some time in laptop platforms that support that form factor. Because M.2 and mSATA cards are different form factors and have different connectors, they cannot be plugged into the same devices.
M.2 SSDs are faster and store more data than most mSATA cards. M.2 SSDs support PCIe 3.0, SATA 3.0 and USB 3.0 interfaces, while mSATA only supports SATA. M.2 SATA SSDs have similar performance to mSATA cards, but M.2 PCIe cards are faster. SATA SSDs have a maximum speed of 600 MB per second, while M.2 PCIe cards can hit 4 GB per second.
PCIe support also allows M.2 cards to take advantage of the non-volatile memory express (NVMe) protocol. An NVMe drive provides a large performance advantage over drives based on other types of interfaces due to reduced latency, increased input/output operations per second (IOPS) and lower power consumption.
As of early 2020, the largest M.2 SSDs support 2 TB of capacity, which is more than any mSATA drives but considerably less than other types of SSDs, such as 2.5-inch drives.
M.2 connectors support four lanes of PCIe bandwidth, or one SATA or USB lane.
M.2 SSD form factor
M.2 SSDs are rectangular. They are 22 millimeters wide and usually 60 mm or 80 mm long, although there are also 30 mm, 42 mm and 110 mm length cards. Longer length M.2 drives usually hold more NAND chips for extra capacity than the shorter versions. M.2 drives can be single- or double-sided. The card size is identified by a four- or five-digit number. The first two digits are the width and the remaining numbers are the length. For example, a 2260 card is 22 mm wide and 60 mm long.
The 22 mm width is standard for desktop and laptops. An 80 mm or 110 mm length card can hold 8 NAND chips for 2 TB of capacity.
M.2 module keys
Keys, notches in the edge connectors of M.2 modules, distinguish the types of M.2 products.
M.2 SSD modules plug into circuit boards through mating connectors on either side. Unlike mSATA, M.2 SSD cards have two types of connectors, also known as sockets: B key sockets and M key sockets. A single card can also have B and M keys. The type of key determines the number of PCIe lanes the socket supports. A B key holds one or two PCIe lanes, while an M key holds up to four PCIe lanes. The B key edge connector is six pins wide and the M key edge connector is five pins wide.
For Wi-Fi and Bluetooth wireless adapters, M.2 cards are keyed for A and E slots in a motherboard. Most M.2 wireless cards support both A and E key slots.
M.2 SSD pros and cons
Size and capacity are two of the M.2 SSD form factor's greatest benefits. In a laptop, for example, an M.2 SSD takes up far less space and uses much less power than a standard SATA or SAS interface 2.5 inch solid-state drive. But if massive storage capacity is required in a mobile device, other form factors will likely be a better fit.
M.2's performance is also a key feature. An M.2 SSD that is based on the NVMe spec can read and write at much faster rates that SATA or SAS SSDs.
M.2 interface is kind of a Swiss army knife of a connector, with the ability to support PCIe, SATA, USB 3.0, Bluetooth and Wi-Fi. So, if a laptop with an M.2 interface or two is purchased, there will be a lot of configuration options for peripheral gear.
The main drawbacks to M.2 SSD storage are price and lack of ubiquity. Prices for 2.5 inch SATA SSDs have plummeted as they have been produced in greater numbers. Currently, a 1 TB SATA SSD will cost about $100 or less; the price of an M.2 SSD with comparable capacity is about two and a half times the cost of the SATA drive.
Another shortcoming of M.2 SSDs is limited capacity. While 1 TB or 2 TB is probably adequate for most mobile applications, higher capacities will be required for M.2 to find its way into more enterprise storage systems.
M.2 SSD purchase considerations
The first consideration when planning to purchase an M.2 device for a computer is whether it has one or two M.2 plugs.
M.2 cards are typically used in newer mobile computing devices. Because the form factor is different from mSATA cards, M.2 SSDs are not compatible with older systems. And because it is designed for mobile devices, M.2 may not be a fit for large enterprise storage systems. However, enterprise storage vendors are beginning to incorporate M.2 SSDs in their hybrid and all-flash storage arrays. Even with limited capacities, the size and density of M.2 SSDs still allow storage vendors to pack a lot of high-performance capacity into a small box.
If a laptop is compatible with the M.2 spec, it will have the physical interface, and the device's operating system should already include the required Advanced Host Controller Interface (AHCI) drivers to allow installation of the M.2 storage card. It may also be necessary to make an adjustment in the device's basic input/output system (BIOS) so that it can recognize the M.2 storage.
For desktop computers that are not equipped with M.2 interfaces, adapter cards are available that plug into a PCIe slot and then can accommodate M.2 form factor cards.
It's becoming more common for flash memory to be used in secondary storage systems to enable speedier recoveries when computing operations have to switch over to backup, or secondary, storage during data center outages. Using solid-state drives in secondary systems helps to ensure that business can proceed at appropriate pace, even when it's running off backup systems.
The price of a 2 TB M.2 SSD typically ranges from $230 to $400; lower capacities are considerably less expensive (e.g., 256 GB M.2 SSDs are available for around $50). Samsung sells a variety of M.2 SSDs in different capacities. Other M.2 SSD vendors include Toshiba, Kingston, Plextor, Team Group, Adata and Crucial (owned by Micron). Intel is the largest vendor for M.2 wireless adapters.