M.2 interface description

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1. SSD Dimensions and Specifications
When we buy ssd, merchants will say whether the ssd is 2280 or 2242. The specification here is actually the size of the represented ssd.


There are currently 11 sizes of M.2 modules, represented by Type xxyy, where xx represents the width, and yy represents the length, in millimeters. For example, Type 2230 mentioned above means its width is 22nm and its length is 30nm; Type 2242 means its width is 22mm and its length is 42mm; Type 2280 means its width is 22nm and its length is 80nm. Currently, there are three common types of M.2 SSDs, namely 2230, 2242, and 2280.

2. SSD interface
According to the interface type, the m.2 interface can be divided into Socket 2 and Socket 3

Socket 2 can also be called B key, support sata, pcie x2

Socket 3 can also be called M key, support sata, pcie x4




The B key's foolproof key is on the left of the slot, and the M key is on the right. The number of pins on the short side of the two types of sockets is different




At the beginning, the B key can only be inserted into the b key (Socket 2) interface, and the m key can only be inserted into the m key (Socket 3) interface, but with the popularity of the m key interface, more and more The computer motherboard only has the m key interface, and the ssd of the b key cannot be inserted at all, so the manufacturers have designed an ssd with the b&m key interface.

The b&m key interface can be plugged with b key or m key. The channel supported by b&m key is the same as the channel supported by b key, which is sata pcie x2, but b&m key can be compatible with both m key and b key, while b key can only be compatible with b key, which leads to the fact that b key has no No advantage, b key is replaced by b&m key, now there are only two m2 ssds on the market, b&m key and m key, and b key m2 ssd has disappeared

It is worth noting that there are three types of gold fingers for SSDs: b key, m key, and b&m key, but the m.2 interface on the motherboard only has two types: b key and m key.

When the m2 interface on the motherboard is the b key, only the b&m key and b key ssd can be plugged in, and the m key cannot be plugged in, as shown in the figure below:






When the m2 interface on the motherboard is the m key, only b&m key and m key ssd can be plugged in, but the b key cannot be plugged in, as shown in the figure below:




3. SSD protocol
According to the agreement, m.2 ssd can be divided into ssd using sata channel and ssd using pcie channel. Note that only the ssd with m.2 interface is discussed here. Even if the ssd is with m2 interface, the sata channel and pcie channel are also separated.

First of all, we need to know that nvme and ahci are protocols. The nvme protocol is specially designed for solid-state drives with pcie channels, and achi is specially designed for hard drives with sata channels. Both pcie and sata are channels.

Now more and more people call the achi protocol as the sata protocol, and we will use the name of the sata protocol below.

There are two types of m2 interface, one is through sata (achi), and the other is through pcie (nvme).

The speed of using sata is the same as that of the traditional sata interface, that is, the interface has become m2.

The one that uses pcie is what we call nvme, and its performance is much stronger than sata.

Generally speaking, when buying m.2 ssd, merchants will clearly mark those that support nvme (because this is a big selling point), and those that do not support are generally not marked.

According to our understanding of the m2 interface model above, we know

B key supports sata, pcie x2.

M key supports sata, pcie x4.

b&m key supports sata, pcie x2.

Here is a direct conclusion. Among the ssds you can buy on the market, most b&m key ssds do not support the nvme protocol, but only support the sata protocol. All m key ssds support the nvme protocol, (as for the b&m key The ssd of the key has now been eliminated and will not be discussed here)

Most b&m key ssds do not support the nvme protocol, only the sata protocol

As technology advances, such ssds will become less and less. Therefore, when we buy ssds, most b&m keys support sata protocol, but not nvme.

To sum up, we have two ways to judge whether an ssd supports the nvme protocol

The first and most direct method is to directly check whether nvme is written on the ssd. If it is written, it is supported, and if it is not written, it is not supported. In this way, you don't need to care about the interface of the ssd.

The second is to observe the interface of the ssd. If we get an m key ssd, we can directly determine that it supports nvme. If we get a b&m key ssd, we can’t tell. I can only say that most b&m keys are It does not support the nvme protocol (supports the sata protocol).

4. Compatibility

The ssd can be plugged into the m.2 interface on the motherboard, which is only the minimum requirement for compatibility. Some ssds cannot be used normally even if they can be plugged in. You need to understand the design of the motherboard in detail, and analyze specific problems. Before buying an SSD, you should ask in detail whether the motherboard is compatible with the SSD you purchased.




To sum up, when we buy an ssd, we need to understand two issues.

1. Whether the ssd can be plugged into the m.2 interface on the motherboard, this is only the minimum requirement for compatibility

2. Ask the merchant to see if the design of the motherboard is compatible with the ssd you bought

When buying ssd, compatibility issues are the most troublesome for consumers. Different manufacturers have different ssd designs. As a piece of hardware, when the interface can be plugged in, there are still cases where it cannot be used. The design of this interface is very failed. I believe that in the near future, as the standards become more and more standardized, this phenomenon will gradually disappear.