The M.2 standard for SSDs is new, exciting, and promising. First, let’s look into why it was needed in the first place.
SSDs, and the Need for M.2
SSDs or Solid State Drives are flash storage devices that have, for the most part, replaced their predecessors (the more traditional HDDs). SSDs are faster, lighter, and take up much less space inside your PC.
In the past few years, there have been many new SSD releases. The problem is that sometimes the buses that these drives are connected to cannot keep up with how fast they are. There’s really no point in having a more capable drive if those same capabilities are being hindered by the interface that it’s connected to.
To solve this problem, we can use a number of different standards, such as the SATA Express. The M.2 standard, however, has been the most efficient so far and shows the most potential. So let’s take a look at how it works.
What exactly is M.2?
The M.2 standard was initially called the Next Generation Form Factor or NGFF but later came to be known as simply M.2. It is used in space-constrained devices like mini laptops and ultra-thin ones. It improves on the mSATA standard and adds features like a reduced module footprint.
You can connect an M.2 SSD module to a host either through a SATA interface or a PCI Express (PCIe) lane, because M.2 supports both (although it can only be inserted in one of these, so it is always a good idea to check your motherboard beforehand to see which one you have) and whether it’ll work with the M.2).
Comparing M.2 to its Predecessor: mSATA
The mSATA interface was designed for the same devices that now work better with M.2. The idea was to create a thin enough profile card, but one that still worked with the SATA interface. Things were all good until it became evident that the SATA 3.0 standards were limiting the performance of SSDs.
The M.2 standard was thus created using SATA 3.2 specifications, which is what the SATA Express uses as well. More than anything else, M.2 provides a certain versatility that mSATA alone never could, which you will realize as we talk about the M.2 vs SATA debate.
Under the SATA 3.0 specifications, the effective bandwidth of any SSD being used with that interface is restricted to around 600MB/s. Most drives can easily cross this speed. The mixed approach provided by SATA 3.2 allows M.2 to either stick to the existing SATA 3.0 specs and their measly 600MB/s, or switch to using PCI-Express instead, and enjoy PCI-Express 3.0’s 1GB/s bandwidth.
A fun twist here is that this 1GB/s is for a single PCI-Express lane. The M.2 standard allows you to use multiple lanes, so using two or four lanes (for instance) would effectively double and quadruple this bandwidth. Again, this depends on the device you’re using. Some systems will only allow two PCI-Express lanes, and so on.
It is really their speed which allows SSDs to be used for gaming and other resource-heavy activities which involve a lot of data being copied over from the storage to the RAM.
SSDs are already thinner and lighter than hard drives, but M.2 drives reduce the overall size of storage devices even further. For one thing, the cards are narrower than they were for the mSATA form. mSATA cards are 30mm and 50mm in width and length respectively, whereas M.2 cards are 22mm and 30mm.
However, while most mSATA drives come in standard sizes, M.2 cards range from the size mentioned here, to ones that are 110mm in length. Increased lengths provide space for more chips and hence more capabilities. M.2 boards can also be either single or double-sided, which further increases these capabilities.
SSDs alone, again, do a lot to reduce the energy consumption in mobile computers. Such computers only have limited runtimes, which depend on the power drawn by various components, including, of course, storage. The reduced energy consumption by SSDs was good, but not enough. The SATA specs in M.2 drives also introduce features like DevSleep, which helps extend runtime even further.
More to Consider: NVMe drives
The second debate that we look into is the NVMe vs M.2 question. NVMe stands for Non-Volatile Memory Express, and it is also a standard designed for SSDs, for the similar purpose of allowing them to read and write data at the speeds that they are actually capable of. It forgoes SATA altogether by allowing your drive to connect to your PC directly through the PCIe interface.
To clear up any confusion, in short: M.2 can work with either NVMe or SATA, but results aren’t the same for both combinations. We’ve talked about the first combination, now let’s see how M.2/NVMe are different together.
The Defining Factor: Command modes
The command structure used in SATA called AHCI or Advanced Host Controller Interface is somewhat problematic. Even though it results in a simpler user interface, the single command queue (with 32 commands) in AHCI drivers restricts the performance of SSDs.
NVMe attempts to solve this problem by providing up to 65,536 command queues with up the 65,536 commands per queue. This means more parallel processing is possible than was with the AHCI system. M.2 does allow you to use both the NVMe and the AHCI drivers, but switching between the two will require that you reformat them first.
Problems with M.2
M.2 sounds like a dream when you first hear about it, and in some ways it is, but it does have some problems, at least for now, such as these.
Older Operating Systems
The NVMe command mode perk cannot be utilized by everyone. AHCI comes pre-built into modern operating systems, but NVMe drivers need to be installed and this may not be possible with older operating systems.
Problems with Booting
As you know now, using the PCIe bus is the way to have the best M.2 experience, but this isn’t always possible. SSDs are best used as boot drives, but older Windows versions don’t allow drives to boot using PCIe instead of SATA.
This leaves you stuck with a boot drive that is still as slow as any SATA 3.0 drive. Even combined with a faster data drive, you won’t have optimum results. Windows 10 doesn’t have this issue though, and neither does Apple OS X.
M.2 Limits Other Features
Depending on how you’re using M.2, other options may become limited. For instance, all your SATA or PCIe lanes could be used by the M.2 drive slot. Even if the lanes are shared with expansion cards, problems still arise, so being familiar with the design of your motherboard and its potential is extremely important.