The rise of SSDs is an unstoppable trend—a sweeping revolution destined to replace traditional HDDs. The triumph of this transformation is not far off. In this ongoing storage revolution, SSD interfaces are also continuously evolving to deliver faster speeds and better user experiences. Mainstream SSD interfaces now include SATA, M.2, PCIe, and mSATA. But what are the differences between these interfaces, and which platforms are they best suited for?
SATA 3.0 Interface: Now the Most Common SSD Interface
The SATA interface is the most widely used hard drive interface today. Its biggest advantage is its maturity. It also offers broad compatibility with devices and a high level of popularity. SATA has evolved from the original SATA 1.0 to the current SATA 3.0. Both regular 2.5-inch SSDs and HDDs use this interface, with a theoretical transfer bandwidth of 6Gbps. This bandwidth is far slower than the 10Gbps or even 32Gbps offered by newer interfaces. Nonetheless, the read and write speeds of a typical 2.5-inch SSD, which can exceed 500MB/s, are more than enough for most users. As for HDDs, the 6Gbps bandwidth is not a bottleneck. Hard drives have evolved very slowly. There has been no significant breakthrough in speed.
Although the SATA 3.0 interface specification is now outdated, ordinary users don’t have overly demanding performance needs, so SATA 3.0 will stay a mainstream choice for quite some time. There are quite a few representative SATA SSD options. These include the Intel 730 series, Samsung 850 PRO, and Plextor M6Pro, among others. Especially the Samsung 850 PRO, which signifies the pinnacle of SATA 3.0 SSD performance.
Yet, akin to notebook hard drives, the 2.5-inch form factor has a large amount of empty space when opened. It leads us to question: why not make a smaller-sized SATA SSD? This is where mSATA came into play.
mSATA Interface: Much Ado About Nothing
The history of mSATA is actually quite long. The “SATA-IO (International SATA Association)” introduced the new Mini-SATA interface controller specification in 2009. This new controller allowed SATA technology to be integrated into smaller devices. mSATA would offer the same theoretical interface transfer speeds as the current SATA interface standards. These speeds are namely 3Gb/s and 6Gb/s.
Intel actively promoted mSATA SSDs due to their small size, ultra-thin form factor, and space-saving nature. The company marketed them as storage devices for ultrabooks and other thin portable PCs. Intel even integrated this interface into some motherboards. With the same transfer standards as SATA 3.0, mSATA offered reliable performance. Its compact size made it the top choice for SSDs in dual-drive laptop configurations at the time.
Nonetheless, after mSATA SSDs were introduced to the market, they did not gain the popularity initially expected. Due to space limitations and fewer NAND flash chips, their performance and capacity couldn’t compete with contemporary 2.5-inch SSDs. Additionally, the small form factor made them more expensive. SSD technology was still developing, so the lower capacity-to-price ratio and limited standout features were unable to draw consumers. Eventually, mSATA SSDs were relegated to the second-hand market.
No matter the type of SATA 3.0 interface, its speed limitations made the “weakest link” effect increasingly obvious. The market wanted an I/O interface that could exceed the 6Gbps bandwidth. This was necessary to meet the growing demand for high-speed SSD performance. As a result, in recent years, the shift to new interfaces replacing SATA 3.0 began. So, who will be the chosen one?
SATA Express: The Embarrassing Endgame
To break through the limitations of SATA 3.0, the creators of the SATA standard took action. They wanted to offer compatibility with older SATA devices. The SATA-IO (SATA International Organization) developed a new disk interface called SATA Express.
SATA-Express is a hybrid of the SATA interface and PCI-Express. It offers a theoretical bandwidth of 10Gbps. This is 4Gbps higher than SATA 3.0. It is compatible with older SATA standard hard drives and can also support high-speed SSDs using the SATA-Express interface. Each SATA-Express interface can connect to one SATA-Express hard drive or two SATA hard drives.
The 9-series motherboards lack native support. Thus, the SATA-Express interface controllers are all provided by third-party chip manufacturers. Additionally, the theoretical bandwidth isn’t much higher than that of SATA 3.0, yet it occupies valuable motherboard and interface space. As a result, we are seeing less and less of SATA Express today.
M.2 Interface: A Ray of Hope After the Darkness
During the era when Intel was promoting ultrabooks, a storage interface standard had already been established. Corresponding SSD design standards were also set to suit the ultra-thin form factor. Due to the many limitations of mSATA, Intel had to reconsider its ideal storage device framework. Intel recognized that the mSATA interface could not meet the current development needs. At the 2012 IDF (Intel Developer Forum), they announced the technology standard NGFF (Next Generation Form Factor) for SSDs. This new standard was introduced to improve technology. It aimed to further reduce thickness. It also sought to increase transfer speeds to meet the demands of the new generation of ultrabooks.
Since NGFF was not concise enough, it was later renamed the M.2 interface. Compared to the SATA interface, the M.2 interface offers more advantages in terms of transfer bandwidth, capacity, and thinness. Today, the M.2 interface is no longer limited to ultrabooks. It has also made a strong impact in the DIY PC building market. As early as with Intel’s 9-series motherboards, M.2 interfaces were included, and by now, with the 100-series motherboards, it has almost become a standard feature.
Why can M.2 lead the speed revolution in SSDs? The reason lies in the fact that the M.2 interface uses the PCI-E lanes, rather than the traditional SATA lanes. As we know, mainstream motherboards have plenty of PCI-E lanes available, which means multiple lanes can achieve ultra-high bandwidth. This is why PCI-E lanes have become the interface standard for the next generation of SSDs.
In terms of size, M.2 comes in three specifications: 2242, 2260, and 2280, which are defined based on the different lengths of the products. A longer length means a larger capacity, as more flash memory chips can be arranged in a longer space. For example, in the M.2 2242, “22” refers to a width of 22mm, and “42” refers to a length of 42mm. The same principle applies to the 2260 and 2280 models. Hence, before purchasing, it’s important to check which length of M.2 SSD your device supports.
Now, M.2 interfaces are divided into two types: Socket 2 and Socket 3. Socket 2 uses the SATA channel and PCI-E 2.0 x4 lanes, with highest theoretical read and write speeds of 700MB/s and 500MB/s, respectively.
Socket 3 is specifically designed for high-performance storage, using PCI-E 3.0 x4 lanes. It can achieve speeds of up to 32Gbps. This translates to nearly 4GB/s in bandwidth. It is five times faster than SATA.
It’s important to note that Socket 2 supports two types of channels: SATA and PCI-E. For example, the Plextor M6e uses a high-speed PCI-E x2 storage interface, while the Plextor M6GV, also an M.2 interface, uses a SATA storage interface. So, there is a clear performance difference between the two.
As for Socket 3, besides utilizing the PCI-E 3.0 x4 high-speed lanes, it achieves ultra-fast transfer speeds. It also addresses the latency issues inherited from mechanical hard drives. Speed and latency are key performance indicators for storage devices. We know that three major factors contribute to hard drive latency. These factors are the storage medium itself, the controller, and the software interface standard. As a result, the new transmission protocol NVMe, which replaces AHCI, has emerged to influence the next generation of SSDs.
The NVMe transmission protocol is completely new. It was developed based on the characteristics of flash memory. It understands SSDs far better than AHCI. It allows the hard drive to connect directly to the CPU via the PCIe interface. This connection avoids the traditional method of going through the southbridge controller before reaching the CPU. This enables faster SSD transfer speeds and lower data latency.
The number of queues in NVMe has been increased from 1 in AHCI to 64,000. This change greatly improves the SSD’s IOPS (In/Output Operations Per Second) performance. It also introduces features like automatic power state switching, dynamic power management, and driver-free operation.
Overall, the performance of M.2 SSDs with Socket 3 interfaces far exceeds that of any current SSD interface standard. For example, the Samsung 950 PRO 256GB M.2 SSD has read and write speeds of an astonishing 2300MB/s and 951MB/s, far surpassing SATA SSDs. To make classification easier, we refer to these high-performance M.2 SSDs as NVMe M.2 SSDs.
With explosive performance and high prices, NVMe M.2 SSDs have become the benchmark for the future development of SSDs. Many SSD manufacturers are already tracking this market trend, eager to grab a share of the pie. We believe the future belongs to NVMe M.2 SSDs.
PCI-E Interface: The Other Side of M.2
PCI-E SSDs are not some black technology, as they originally use PCI-E 3.0 x4 lanes and support the NVMe interface standard. In other words, PCI-E SSDs are more “pure” compared to M.2 SSDs. For example, the Intel 750 is a purely PCI-E SSD.
Of course, some manufacturers convert M.2 SSDs to PCI-E SSDs by connecting them to PCI-E adapter cards with M.2 interfaces. Since the interface standard is the same, the performance is also the same. That’s why we say that the PCI-E interface is essentially the other side of M.2.
U.2 Interface
The U.2 interface, originally called SFF-8639, was primarily driven by Intel. It is essentially based on SATA Express. The SATA-E physical interface is modified from the SATA 6Gbps interface. This modification is somewhat akin to the SAS interface. It uses two SATA 6Gbps interfaces. It also uses a mini SATA interface with only 4 pins. The small interface can only connect to PCI-E lanes. The main advantage of this design is that it maintains downward compatibility. This is crucial because there are presently very few SATA-E drives available.
The design concept of the U.2 interface is like SATA-E, aiming to make the most of existing physical interfaces but with faster bandwidth. It upgraded from PCI-E x2 to PCI-E 3.0 x4 and added support for many new protocols, like NVMe, which the SATA-E interface does not support. In this sense, U.2 can be considered the full version of SATA-E.
The device-side interface of U.2 combines the features of both SATA and SAS interfaces. It fills in the gaps left by the SATA interface with extra pins. It also incorporates an L-shaped anti-reversal design. This allows it to be compatible with SATA, SAS, and SATA-E standards. On the motherboard side, the interface is mini SAS (SFF-8643), while the U.2 cable on the device side connects one end to the SATA power supply. The other end connects to the U.2 drive’s data port.
The most distinctive feature of the U.2 interface is its support for the NVMe protocol, offering high speed, low latency, and low power consumption. The bandwidth runs through PCI-E 3.0 x4. It has a theoretical transfer speed of up to 32Gbps. This speed is five times faster than the 6Gbps offered by SATA.
At this point, you think that the U.2 interface is quite like the M.2 interface mentioned earlier. In fact, they use similar standards, which is why U.2 and M.2 share similar names. But, unlike M.2, U.2 is designed for larger-sized drives.
For certain reasons, U.2 SSDs have a 2.5-inch size, which allows them to better integrate with the presently available SATA 3.0 interface solid-state drives. This makes them suitable for mainstream laptops and desktop computers, with considerable potential in the future. Nonetheless, the downside is that there are still relatively few SSDs equipped with U.2 interfaces, and it is still awaiting broader adoption.
Conclude: Choose the right SSD based on your needs.
Today, we briefly covered the mainstream SSD interfaces from start to finish. In this era of unified standards, only one type of SSD is to stay. It will be the long-term mainstream. SATA is beginning to decline, while M.2 is steadily rising. With strong support from manufacturers, it’s believed that the future very well belongs to M.2 SSDs.
We need to plan carefully if we are purchasing an SSD. It is necessary to gradually change the mindset of only choosing non-SATA SSDs. The mainstream SSDs in the future will inevitably break through the 6Gbps bottleneck that has lasted for years. We look ahead to smaller sizes, higher performance, and larger capacity SSDs becoming our mainstream choice.
Finally, here’s a simple summary to see which SSDs are more suitable for which platforms:
- SATA Interface: For older platforms, like 6-series, 7-series, and even 8-series motherboards, it’s recommended to choose SATA SSDs. These SSDs are ideal for upgrades. They offer strong compatibility. They are also backward compatible with SATA 2.0, making them ideal for older platforms.
- mSATA Interface: This interface is essentially being phased out, with few manufacturers releasing new products. The ones available are often old stock. mSATA interfaces are no longer included in 9-series or 100-series motherboards. Only some older platforms or laptops that originally had mSATA interfaces consider upgrading with it.
- SATA Express Interface: Ignore this. It has no compatibility support and no products available.
- M.2 Interface: This interface is now very popular, with many products available. The price difference is not significant compared to regular SATA SSDs. If you’re building a new system and your motherboard happens to have an M.2 slot, it’s highly recommended to opt for an M.2 SSD. For example, Intel’s 600-series, which offers fast speeds and affordable prices, is a great choice.
- PCI-E Interface: Now, PCI-E SSDs are positioned as high-end products with a high price tag. They are not recommended for mid-range or low-end platforms. The available PCI-E slots are limited. Additionally, the cost is quite high. For the price of one SSD, you can get an entire platform, which is not worth it. If you have a high-end platform, these performance monsters are worth trying. Don’t mind the cost, and you’ll surely be impressed.
- U.2 Interface: The U.2 interface is still in the “concept” stage, with limited motherboard support and even fewer U.2 SSDs available. You rarely see U.2 SSDs in the market at the moment.