M.2: A Compact SSD Form Factor and Fast Bus Interface

As technology advances each day, the terms get geekier and tougher to understand. Data storage is one particular area that continues to witness tremendous growth. It has shifted from spinning disks to IC chips on circuit boards. While almost everyone is conversant with SSD, there's more to learn about Solid-State Drive performance. If you are building a high-performance computing system, speed is a crucial factor and, therefore, you need to consider M.2 SSDs. But what are M.2 SSDs? Take a look! We have looked at them in detail below, plus how they compare to their predecessors.

What are M.2, PCIe (NVMe), and SSD?

We need to go back and start with the Hard Disk Drive (HDD) to understand these terms. HDDs had magnetic disks for storing data coupled with a read/write magnetic head.

SATA and SATA III

HDDs used SATA (Serial Advanced Technology Attachment) as the interface or computer bus for transmitting data between them and the motherboard.

The latest interface used for hard drives was SATA 3.0, and the software interface standard (driver) used to communicate with SATA 3.0 was AHCI (Advanced Host Controller Interface).

Because the HDDs are electro-mechanical, they are relatively slower than SSDs, which use flash memory. SSDs used SATA 3.0 initially, but it led to slow speeds.

An HDD vs. SSD (old vs. new)

Engineers built SATA for HDDs, so it did not allow SSDs to deliver optimal performance. Therefore, when SSD storage came of age, it was necessary to improve its interface to cope with its fast throughput speeds.

An HDD and SSD. Note the size difference.

mSATA

The first improvement was the mSATA (mini SATA). In terms of form factor, these SSDs were smaller. Compared to the 2.5-inch (63.5mm) SATA 3.0 SSDs, mSATA SSDs measured 30 x 50.95mm (full-size) and 30 x 26.8mm (half-size).

However, the performance of the two is similar. The SATA 3.0 protocol has a throughput of 600MB/s, and the mSATA interface matches this, reaching speeds of up to 6Gb/s.

A SATA SSD

Therefore, the only advantage was the size, which made the interface more practical for SSDs because it enabled them to fit in smaller devices.

Technically, 600MB/s is equivalent to 4.8Gb/s (1 Byte = 8 bits), but using the 8b/10b encoding, SATA has a theoretical throughput of 6Gb/s.

PCI and PCIe

PCIe (Peripheral Component Interconnect Express) is also a high-speed bus standard for computer expansion and a popular choice for several devices, such as a graphics card, SSD, Wi-Fi card, Ethernet hardware, etc.

The standard became popular because it provided a direct connection to the CPU. SATA first transfers data to the memory, then from memory to CPU, and vice versa. SATA also relies on cables to connect to the power supply and motherboard.

Compared to PCI, PCI Express is a serial interface with a higher frequency, which means it gives the connected devices a dedicated link to the processor with duplex communication. The result is a higher transmission rate and quality.

PCI has a parallel interface or architecture, which means a shared connection, hence limited bandwidth on the bus.

mPCIe

It was necessary to look at PCI and PCIe to understand the origins of mPCIe (mini PCIe). Since the standard relies on the PCIe architecture, it was an improvement to mSATA SSDs, providing multiple direct lanes or buses to the CPU. It has one PCIe lane and a USB 2.0 signal, enabling it to attain transfer speeds of up to 8Gb/s.

Such performance benefits made it the popular choice for SIM, Wi-Fi & Bluetooth cards, and several I/O expansion slots. However, the form factor is similar to mSATA for both the ports and SSD card size, so it is almost impossible to differentiate them.

It is important to note that the mini versions of PCIe and SATA were improvements from the larger PCIe and SATA form factors, respectively( compact is better). But the performance was the same.

M.2 Connector

Both mPCIe and mSATA provide quick data transmission speeds, and they were dominant in the SSD industry on small form factor devices. However, M.2 came along and is quickly turning the two into legacy technologies due to its high performance.

Intel introduced the M.2 interface in 2012 as the NGFF (Next Generation Form Factor), and it utilizes the NVMe protocol (Non-Volatile Memory express). This protocol has four PCIe lanes, and each of these lanes has a 16Gb/s data transfer rate, resulting in 64Gb/s.

A 512GB NVMe M.2 SSD

Therefore, M.2 is super fast compared to mPCIe and MSATA. The connector can have two to four PCI Express lanes, but two channels (32Gb/s) are still quick.

Even though the technology is expensive, it makes sense to migrate to it because modern high-end technologies like AI and real-time processing applications require quick, reliable, low latency data transfer speeds to operate smoothly.

The M.2 interface is also flexible because:

• The bus interface supports USB, PCIe lanes, and SATA
• The logical interface supports SATA and NVMe to make legacy and modern technologies compatible
• It has diverse applications, such as in SSDs, performance accelerator, expansion, and wireless cards

M.2 SSD

With the M.2 expansion slot came the M.2 SSD. The SATA International Organization and the PCI Special Interest Group defined the M.2 form factor specification, and even though it integrates several devices, it is commonly associated with SSDs.

An M.2 SSD connects directly to the motherboard via the M.2 slot. You can use an M.2 SSD with SATA or PCIe protocols, but these limit its performance. It is best to use it with the NVMe protocol, which accelerates the data transfer speeds between itself and the client systems.

An NVMe M.2 SSD

M.2 SSDs can be single or double-sided. The former is thin and ideal for ultra-slim computers, but it has a low storage capacity. On the other hand, double-sided M.2 SSDs are thicker but feature high storage capacity. However, most M.2 SSDs have a maximum storage capacity of 2TB.

M.2 Form Factors and Keying

M.2 expansion cards have several form factors, but most have a 22mm module width. Some of the sizes include the following:

• 22 x 80mm
• 22 x 60mm
• 16.5 x 30mm
• 22 x 42mm
• 22 x 30mm
• 30 x 30mm
• 30 x 42mm

When buying such a card, you will encounter the sizing code, which factors in the width and length in that order. For example, 2280 implies the card is 22mm wide and 80mm long. Since the sizes are many, it is vital to check which one your computer's motherboard supports, especially when upgrading.

Apart from the size and mounting screw position, keying is a critical factor to consider.

Keying

The keys or pins/contacts are not the same in all M.2 ports. Some of the most common ones are A, E, A+E, B, M, and B+M.

A and E

An A-key has four pins on the left, followed by a gap, then the rest on the right side for the host controller. It is common in cellular modules, Wi-Fi, and Bluetooth cards. The interface supports USB 2.0, I2C, 2x PCIe x 1, and DisplayPort (DP) x4 slots.

An A key M.2 SSD. Note the four pins on one side.

On the other hand, an E module key has 12 pins on the left, followed by a gap, then the other pins on the right for the host controller. Its application areas are similar to A key's, but it supports USB 2.0, I2C, 2x PCI x 1, UAT, SDIO, CNVi, and PCM.

The A+E key combines the features of A and E. It places a 4-pin and 12-pin gap on the left side, while the pins on the right side are for the host controller. It is compatible with A and E M.2 motherboard slots.

B and M

A B module key has six pins on the left, followed by a gap, then the rest of the pins on the right side for the host controller. They are common in PCI express x2, SSDs, and SATA. The interface supports SMBus, PCIe x2, USB 2.0/3.0, HSIC, SATA, I2C, UIM, and SSIC.

On the other hand, an M key has five pins on the right side, followed by a gap, then the other pins on the left for the host controller. It is common in NVMe SSDs & PCIe x4 and supports SATA, SMBus & PCIe x4.

B+M combines the two, with a 6-pin gap on the left side and a 5-pin gap on the right side. The center pins are for the host controller, and such a card is compatible with B and M M.2 motherboard slots.

How to Install An M.2 SSD Drive?

Before getting into the installation, disconnect the computer from the wall outlet or remove the battery if it is a laptop. Also, apply the required anti-static precautions, then follow these steps:

• Pick the suitable SSD
• Check the motherboard to identify the M.2 connector

• Try using an adapter if there's no M.2 connector
• Install the M.2 SSD
• Enable the M.2 device in the BIOS/UEFI PC settings

What Are The Benefits Of M.2?

• Super compact module
• Energy efficient
• 50%-650% faster than SATA
• Flexible measurements to fit different motherboards
• Blazingly quick specifications

Which SSD Is Best to Use?

It depends on the following factors:

• Technical constraints: The SSD interface should match the one on the motherboard. Old devices usually don't have the fast M.2 (NVMe) interfaces, so SATA or PCIe SSDs might be best. You can fit an M.2 SSD on the interface, but you won't get high-performance speeds.
• Price: PCIe NVMe (M.2) are more expensive than SATA and PCIe. If you are on a budget, go for SATA or PCIe SSDs.
• Capacity: Although M.2 SSDs have high bandwidth, most have a 2TB max capacity (a few go up to 8TB). However, SATA SSDs can go up to 16TB. If you want more space, pick SATA SSDs.
• Speed: If you are after high performance, M.2 (NVMe) SSDs are the fastest.

Summary

In conclusion, the M.2 form factor has made data storage devices more compact. But most importantly, it has drastically increased memory bandwidth. Although expensive, the technology makes sense for modern, high-speed computing. If you need any more information about M.2 or need such devices for your project, contact us for more details.