M.2 M vs M.2 (B+M): What's the Difference? - MiniTool Partition Wizard (2024)

Some users may be curious about SSD M.2 M vs B+M when choosing an M.2 SSD. Will they affect SSD speed? To make this problem clear, you should read this post, in which MiniTool Partition Wizard shows you their differences.

M.2 M vs B+M

Nowadays, M.2 SSDs are more and more popular among users. When it comes to M.2 SSDs, some people will label them with high speed. However, this is not so absolute. You should take the interface into consideration.

If you search M.2 SSD products online, you will find that most of M.2 SSDs look like the following two items:

The obvious difference between the two SSDs is their pin layouts (so-called ‘key’). The upper SSD in the picture uses M.2 B+M key, while the lower SSD uses M.2 M key. Why do they use different keys? The reason is that they use different Bus.

In general, M.2 SSDs have three types of keys: B key, M key, and B+M key. But later, B+M key combines B key and M key and then it substitutes B key. Please look at the following picture:

The reason why B+M key can substitute B key is that they support same Bus (SATA or PCIe x2). Similarly, the reason why B+M key can’t substitute M key is that they support different Bus. M key usually support PCIe x2/x4.

Please look at the following picture:

An M.2 B+M key SSD may support SATA bus or PCIe x2 bus. If the SSD only supports SATA bus (so-called M.2 SATA SSD), its speed will not exceed 600 MB/s. If the SSD supports PCIe x2 bus, its speed will be around 1000 MB/s.

As for the M key SSD, when it runs PCIe x2 bus, the speed is around 1000 MB/s; but when it runs PCIe x4, its speed may exceed 2000 MB/s. Therefore, in most cases, M.2 M key SSDs are faster than M.2 B+M key SSDs.

Should I Choose M.2 M or B+M Key SSD?

After reading the above content, you can see the difference between M.2 M vs B+M. Then, which one should you choose? Considering performance, you may like to choose M.2 M key SSDs.

However, when you plan to buy an M.2 SSD, you must take M.2 slot into consideration. In a computer, there is only an M.2 B-key socket or an M.2 M-key socket, but no M.2 B+M key socket.

Before you buy an M.2 SSD, you should check which type of slot your computer is using. An M.2 B key slot is only compatible with B+M key SSDs, and an M.2 M key slot is compatible with both B+M key SSD and M key SSD.

The last but not least, you should check whether the M.2 slot supports PCIe (check in motherboard information). If it is PCI Express, please check whether it supports 2x or 4x PCI-Express. After getting these details, you can then buy an M.2 SSD without worries.