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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, originally known as the Next-Generation Form Factor (NGFF), is pronounced M-dot-2.
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 International Organization. The M.2 specification supports applications such as Wi-Fi, Universal Serial Bus (USB), PCI Express (PCIe) and Serial ATA (SATA).
SATA M.2 is 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 nonvolatile memory express (NVMe) protocol, which brings a large performance advantage over other types of interfaces due to reduced latency, increased IOPS and lower power consumption.
As of early 2017, the largest M.2 SSDs support 1 TB of capacity, more than any mSATA 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 (mm) 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 1 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 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 is not a fit for large enterprise storage systems.
M.2 SSDs typically cost from $0.25 to $0.75 per gigabyte. Samsung sells a variety of M.2 SSDs available 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.