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Recently, additions to the available form factors and interfaces of storage drives have created more options for computer users. A pair of changes can be confusing to some users, however. This article explains more about what the M.2 form factor is and how it interacts with various interfaces.

M.2 form factor

M.2 is a form factor specification, designed to replace the mSATA standard. The specification spells out the physical size and shape of the card. The card itself can be used for multiple applications, but this article focuses on solid state drives.

The M.2 form factor has been designed to maximize PCB (printed circuit board) space while minimizing the footprint of the M.2 module itself. The module is rectangular, with possible widths of 12, 16, 22, or 30 millimeters. Generally, solid state drives are 22 millimeters wide. Lengths can also vary: 16, 26, 30, 38, 42, 60, 80, or 110 millimeters. Most motherboards will accommodate a variety of lengths for an M.2 module. The width is more fixed on motherboards as the connector is placed on the edge of the short side of the M.2 card.


M.2 SSD in a laptop

What is PCIe?

PCIe, also known as PCI Express® or Peripheral Component Interconnect Express, is a high-speed serial bus used in computers. This is a physical connection that transmits information and data from one device to another within the computer or between the computer and a peripheral piece of equipment.

The specifications for the PCIe interface are maintained and developed by the PCI Special Interest Group, a consortium of more than 900 companies that work together to form a common standard.

PCIe performance

The implementation of multiple lanes for the PCIe connection is one of the most important features of the standard. A lane is a single serial data connection, similar to a SATA connection. PCIe uses four lanes for storage devices, resulting in data exchange that is four times faster than a SATA connection.

All of these enhancements come with another benefit: reduced power consumption. The combination of NVME, PCIe, and an SSD's lack of moving parts results in a storage drive that sips power, extending battery life for laptops, notebooks, and tablets.

What is NVMe?

NVMe, NVM Express™, or Non-Volatile Memory Host Controller Interface Specification, is a communication protocol designed specifically to work with flash memory using the PCIe® (PCI Express®) bus. It was created to take advantage of the parallel nature of solid state drives. Combined with the PCIe bus and the increased read and write speeds of NAND technology, the NVMe protocol creates faster non-volatile storage. Learn more about PCIe here.

NVM Express Inc., is a computing industry consortium that was created to oversee the development of standards around this scalable host controller interface.

NVMe performance

The combination of the NVMe protocol and the PCIe connection with an SSD results in read and write speeds that are four times faster than a SATA SSD with a SCSI protocol.

NVMe complements the parallel structure of contemporary CPUs, platforms, and applications. Parallel structure allows more commands to flow simultaneously. NVMe uses an optimized path to issue commands and complete input/output and supports parallel operation with up to 64,000 commands within a single I/O queue and 64,000 possible queues. Older protocols such as SCSI are serial in nature, with a limited number of commands in the single queue.

Because NVMe was designed specifically for the NAND technology used in solid state drives, it takes advantage of how the underlying technology works to make a faster drive.

PCIe and SATA interfaces

M.2 is the form factor of a particular SSD. There is also a physical interface that connects the drive to the rest of the computer. Although there are a fair number of different interfaces, we're going to look at PCIe and SATA.

SATA interface

The SATA, or Serial ATA, interface is older than PCIe, but when it was first developed, it brought important advances to computing, such as hot swapping abilities. SATA for storage drives was developed for hard drives. When solid state drives came on the market, they adopted the same interface so users could easily upgrade their storage drive.

PCIe interface

The PCIe, or Peripheral Component Interconnect Express, interface is a newer interface that features a smaller physical footprint. The real advantage of the PCIe interface is the ability to transmit data on up to four lanes. When combined with the logical interface NVMe®, read/write speeds increase for SSDs compared to using SATA and the AHCI logical interface. 

SSD with PCIe interface

Which interface should I get?

The most important aspect of which interface is right for you is which one will work in your computer. It can be difficult to tell the difference between a PCIe and a SATA connection if you look at the slot on the motherboard. Check your computer specifications to see which interface your computer supports. You can also use the Crucial® Advisor™ tool or System Scanner tool to find a compatible part.

If you have the option of multiple M.2 slots where at least one supports PCIe, choose that slot for an SSD upgrade. PCIe, when combined with NVMe, will result in faster read and write times.

©2019 Micron Technology, Inc. All rights reserved. Information, products, and/or specifications are subject to change without notice. Neither Crucial nor Micron Technology, Inc. is responsible for omissions or errors in typography or photography. Micron, the Micron logo, Crucial, and the Crucial logo are trademarks or registered trademarks of Micron Technology, Inc. . PCIe are registered trademarks  of PCI-SIG. NVMe is a registered trademark of NVM Express, Inc.  All other trademarks and service marks are the property of their respective owners.