M.2 Expansion Slot Fully Explained | The Future Of Compact, Robust Technologies.

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The transition from mSATA, mPCie to M.2

When observing the design of various small form factor devices, there are various interfaces such as mSATA, mPCIe, and more recently M.2 interfaces. These interface terms are related to technologies that enable I/O throughout  and data transfer within the hardware architecture for computers.  However, nowadays, the small form factor interface trend has transitioned from mSATA and mPCIe to M.2 interface, and it is moving fast to meet the demands for faster processing. Therefore, to cope with the development of robust and compact computer interfaces, it’s essential to understand the transition from each interface and what differentiates them in terms of benefits.  

In order to meet the demands for smaller and more compact devices, mini-SATA or mSATA was the early development to shrink the peripheral bus interface for computers. The current mSATA is the minimized version of SATA (Serial Advanced Technology Attachment), so they both use the SATA protocol as the logical communication interface. Mini SATA cards form factors come in 30 x 50.95mm full size and 30 x 26.8mm half-size, much smaller than the 2.5” SATA drives. The small form factors of mSATA cards make them a good fit for SATA storage expansion on space-confined systems such embedded computers, IoT gateways, and industrial panel pcs. With the SATA 3.0 protocol, the mSATA interface can reach 6Gb/s of transfer rate in terms of performance which, makes mSATA a good choice for compact and affordable storage.  

For a while, mSATA  was the popular  mini-expansion bus until mPCIe with PCIe 3.0 was introduced as the small form factor interface alternative. Mini PCIe or mPCIe is the miniaturized version of the PCI Express (Peripheral Component Interconnect Express) interface that utilizies the PCIe lanes in computer architecture The similarity between mPCIe and mSATA is that they both have the same form factor for their cards and slots, which can be confusing when comparing both side-by-side.  However, mPCIe utilizes one PCI Express Lane and USB 2.0 signals. By leveraging the PCIe 3.0 Lane, mPCIe is faster than mSATA, with a transfer rate reaching up to 8Gb/s, providing additional performance benefits.      

Furthermore, with PCIe and USB 2.0 signals, mPCIe has a wide array of applications, more than just a storage expansion bus like mSATA. Initially designed for graphics cards and other peripherals such as WiFi, Bluetooth, SIM cards, and I/O expansion, mPCIe can also support storage expansion. That is why you can find various mPCIe cards in different small form factor devices.    

Despite the dominance of mSATA and mPCIe interfaces within the small form factor devices, the M.2 interface is quickly replacing these legacy interfaces. Today’s modern, compact, and robust hardware often involves various high-end technologies such as AI (Artificial Intelligence) or real-time processing. These high-end technologies require low latency and reliable solutions to ensure their mission-critical applications will run smoothly. As a result, many new products nowadays incorporate the M.2 form factor as their compact and powerful computer bus interface. M.2 is the successor of the mSATA and mPCIe interface in terms of next generation form factors. M.2 interface utilizes multiple technologies, including x2 to x4 PCIe 3.0 Lanes, NVMe (non-volatile memory express), SATA protocol, and USB 3.0 signal. By utilizing NVMe protocol with x4 PCIe Lanes, M.2 devices are incredibly fast compared to mPCIe and mSATA devices. (remove)  

The mSATA and mPCIe standards are quickly becoming legacy technologies with m.2 as its replacement. Today, the m.2 interface is leading the advancement of compact, powerful, and blazing fast computing technologies to the next generation. Therefore, further in this blog, we will provide you a complete overview to recognize the potential of the M.2 slot, M.2 technologies, and M.2 devices in computing hardware technologies.


credits: Toshiba, Mfactors, Samsung                                                                    


What is the M.2 expansion slot?


M.2 expansion slot is the specification for on-board internal expansion cards on a motherboard. Intel first introduced the M.2 slot in 2012 as the Next Generation Form Factor or NGFF.  The M.2 form factor is great for numerous applications from basic wireless cards to complex AI accelerators. In addition, M.2 sockets are much faster than mSATA, thanks to their ability to utilize full PCI Express lanes. The M.2 slots on the motherboard can utilize two to four PCIe lanes, with PCIe 4.0 having a 16Gb/s transfer rate on each lane makes M.2 incredibly fast. As a result, M.2 devices are hundreds of times faster than the mSATA devices.  

Moreover, M.2 bus interfaces, logical interfaces, and device options  are much more flexible than mSATA:

  1. M. 2 bus interface supports PCIe lanes, SATA, and USB.
  2. M. 2 logical interface supports NVMe and SATA interface for modern and legacy technology compatibility.
  3. M. 2 devices have diverse applications such as solid-state drives (SSDs), wireless connection cards, I/O expansion cards, and performance accelerators cards.  

What are the benefits of M.2?  

  • Super compact module – Smallest M.2 devices are 18% smaller compared to smallest mPCIe devices.  
  • Flexible Measurements – some M.2 ports on a motherboard supports multiple lengths of M.2 cards.  
  • Power-efficient – M.2 power consumptions are limited to 7 watts (W).  
  • M.2 devices are much faster than SATA devices – around 50% to 650% faster.  
  • Blazing fast specification: NVMe protocol and PCIe 4.0 with up to x4 lanes (16Gb/s each lane)  


M.2 Expansion Slots | Form Factors and Keying Explained  

The M.2 interface is versatile and supports various M.2 cards with different form factors and socket types. Here, we will explain a wide variety of M.2 form factors and the specific type of keys to help you choose the correct specification of your M.2 devices and M.2 slots on your motherboards.  

M.2 Keying Explained  

It is important to note that not all M.2 ports are the same. When choosing M.2 devices or M.2 ports on a motherboard, you need to pay attention to the key's specifications identified on the motherboard. M.2 keys are the types of edge connectors that differentiate the M.2 connectors. The slot and the device are required to have the same key in order to be compatible. Here are some of the most common M.2 key types (B, M, B+M, A, E, A+E):  

  • B Key: Has a six pins gap at the left side of the card, and the right side is the host controller.  
  • B Key Common Usage: SATA, PCIe x2, and SSD.  
  • B Key Interfaces Support: PCIe x2, SATA, USB 2.0/3.0, UIM, HSIC, SSIC, I2C, and SMBus.  
  • M Key: Has a five pins gap at the right side of the card, and the left side is the host controller.  
  • M Key Common Usage: PCIex4 and NVMe SSD.  
  • M Key Interfaces Support: PCIe x4, SATA, and SMBus.    

B+M Key: Combination of both B Key and M Key with 6 pins gap at the left, 5 pins gap at the right side of the card, and the center is the host controller. B+M Key is compatible with both the B key and M key slots on the motherboard M.2 interface.  

  • A Key: Has a 4 pins gap at the left side of the card, and the right side is the host controller.  
  • A Key Common Usage: WiFi, Bluetooth, and Cellular modules.  
  • A Key Interfaces Support: 2x PCIe x 1, USB 2.0, I2C, and Display Port (DP) x4.    
  • E Key: Has a 12 pins gap at the left side of the card, and the right side is the host controller.  
  • E Key Common Usage: WiFi, Bluetooth, and Cellular modules.  
  • E Kay Interfaces Support: 2x PCI x1, USB 2.0, I2C, SDIO, UAT, PCM, and CNVi.  

A+E Key: Combination of both A key and E key with 4 pins and 12 pins gap at the left side of the card, and the right side is the host controller. A+E Key is compatible with both A key and E key slots on the motherboard M.2 interface.  


M.2 Form Factors  


Most M.2 expansion cards are 22 mm wide, with multiple length options of 30, 42, 60, 80, and 110 mm long. In addition, there are other varieties of M.2 width and length, such as modules with 12, 15, and 30 mm wide and modules with 12, 26, and 38 mm long for smaller form factors. The size coding method of the M.2 devices combines the width and length of a particular module. For example, the "2260" module code means that the M.2 card is 22 mm wide and 60 mm long. Furthermore, you want to make sure your motherboard M.2 expansion slot is compatible with your M.2 module's size and key. For upgradability, some motherboards support M.2 expansion slots with multiple length options by providing different positions for the mounting screw.  


Single-Sided and Double-Sided M.2  


M.2 modules have several thickness levels with single-sided and double-sided modules. The single-sided M.2 modules allow the device to be more compact for space-constrained applications. On the other hand, the double-sided M.2 modules enable more chips to fit into the M.2 PCB (plastic circuit board) increasing the overall capacity for the type of m.2 module. It’s Important to note that both sides of the M.2 modules' thickness cannot exceed 1.5 mm for each side, and the thickness of the PCB is 0.8 mm ± 10%.


How to install M.2 modules on your motherboard?  


credits: Tomshardware

To successfully install your M.2 modules on your motherboard, you want to make sure the M.2 module's form factor matches the motherboard M.2 socket specification. For example, an M.2 module with a specification code of "2240 Key E" requires the same key on the motherboard to have a 22 mm wide and 40 mm long Key E M.2 port. When the module and motherboard have the same m.2 compatibility, you can take off your system's enclosure to access the motherboard with M.2 socket and insert the card at a 30˚degree angle. After inserting the card into the socket, press the card down parallel with the motherboard, then screw the semicircle gap at the end of the card to secure the module on the motherboard. If every step is done correctly, your system should be ready for bootup with your designated m.2 module.  


M.2 Technologies | Signal Interface and Storage Protocol  


credits: PCI Express, Serial ATA, USB, NVM Express

Intel developed the M.2 interface to be highly flexible and powerful for a wide array of applications. M.2 supports multiple signal interfaces such as PCI Express (PCIe 3.0 and 4.0), Serial ATA (SATA 3.0), and USB 3.0. In addition, a variety of bus interfaces enable the M.2 expansion slots to be highly flexible for different applications such as storage applications, performance accelerators, wireless connectivity, and I/O expansion modules.    

Moreover, M.2 supports both SATA (AHCI) and NVMe storage protocol, providing legacy and modern compatibility. SATA is a legacy standard that uses AHCI or Advanced Host Controller Interface as the storage protocol that Intel initially defined to optimize data manipulation on spinning metal disks in an HDD (hard disk drive) storage. In contrast, NVMe or Non-Volatile Memory Express was createdto  take  the full advantage of the flash chip storage (NAND chip) and the PCI Express Lane for super-fast SSD (solid-state drive) storage.

What Applications Can Use M.2?  

With the versatility of the M.2 interface thanks to its support of multiple signal interfaces and storage protocols, there are a wide array of applications that can benefit from M.2 expansion slots. The applications that implement the M.2 form factor are constantly developing, from connectivity modules, storage solutions to performance accelerators. Especially with more and more devices requiring compact solutions, the m.2 form factor is great to meet a variety of applications in both enterprise and consumer workloads.

M.2 Connectivity Modules


credits: Intel, Thales, IO Crest

You can expand your system's wireless and wired connectivity with M.2 expansion ports. There are a lot of wireless cards and I/O expansion modules available in an M.2 form factor. These M.2 cards provide connection expandability in a compact form factor. Here are some of the M.2 connectivity modules you can get today:  

  • M.2 WIFI Card (up to WiFi 6 802.11ax)  
  • M.2 Bluetooth Card (up to Bluetooth 5.0)  
  • Sim Card Module (4G LTE and 5G modules)  
  • I/O expansion modules: COM, LAN, USB, etc.  


M.2 SSD Storage Solutions  


credits: Samsung, Bplus Technology

There are diverse M.2 SSDs available with different sizes and specifications. From a size perspective, M.2 SSDs offered various M.2 form factors depending on their storage capacity. A quick rule of thumb is that the larger the storage capacity, the more NAND flash storage chips they need, leading to a bigger M.2 SSD's size or length previously mentioned. On the other hand, from the specification's perspective, you can get M.2 SSDs either with SATA interface or NVMe interface SSDs.  

The main difference between M.2 SATA SSDs and M.2 PCIe NVMe SSDs is the speed. The SATA interface has a speed bottleneck at a 6Gb/s transfer rate compared to the PCIe 4.0 lane with a 16Gb/s transfer rate for each lane. Moreover, M.2 interface is capable of utilizing x2 or up to x4 PCIe lanes for high-performance, low latency SSDs. M.2 SSDs can transfer data 50% to around 650% faster than the SATA SSDs. When comparing the read and write speed of these two M.2 SSDs, SATA 6Gb/s SSDs have a 550MBps read and write speed compared to the blazing fast M.2 PCIe NVMe SSDs with 3,500Gb/s, and 2,450Gb/s theoretical read and write speed. Here are some specifications of M.2 SSDs you can get today:  

  • M.2 SATA SSD (AHCI Protocol) – 500MB/s read and write speed  
  • M.2 PCIe SSD (AHCI Protocol) – 2Gb/s and 1.5Gb/s read and write speed  
  • M.2 PCIe NVMe SSD – 3.5Gb/s and 2.45GB/s read and write speed    

Important note: NVMe SSDs are extremely fast. You want to get the fastest M.2 SSDs, choose the M.2 SSDs with M Keys since they support PCIe x4 lanes which fully optimize your SSDs speed.  

M.2 Performance Accelerators  


credits: Intel, Coral.AI, Advantech

Besides connectivity and storage expansion modules, performance accelerators have quickly adopted the M.2 form factor to benefit from its compact and powerful interface. These performance accelerators include memory accelerators, AI (artificial intelligence) accelerators, Deep learning accelerators, inferencing accelerators, and more. Here are some of the top M.2 performance accelerators you can get today:  

  1. M.2 Intel Optane Memory – Intel's developed speed-boosting cache storage in an M.2 format. It accelerates cache for another drive to enables high-speed computing.  
  1. M.2 VPU – Intel's Movidius VPU (Vision Processing Unit), developed to enhance machine learning and inferencing for edge computer vision that require robust and compact technologies.  
  1. M.2 TPU – Tensor Processing Unit, developed by Google to accelerate training on large and complex neural network models. A very powerful and energy-efficient AI accelerator in a compact M.2 form factor.

All being said, the incredible speed, compact form factors, and high flexibility of the M.2 interface have opened a vast opportunity for a myriad of computing solutions, from simple solutions to more advance and complex computing solutions such as AI, blockchain, and 5G technologies. It is exciting to see how the Next Generation Form Factor or M.2, PCI Express 4.0, and NVMe technologies will lead the advancement of compact and robust solutions in industrial-grade compute.  

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