The M.2 slot: What is it and how can I use it?

Almost every current mainboard comes with at least one M.2 slot.

But what exactly can you use it for? Is every M.2 slot the same? Are there perhaps alternatives?

This and more you will find out in the following article.

Which physical standards are there?

Due to the M.2 connector, which is permanently soldered to mainboards or adapter cards, the board width of M.2 hardware is always 22 mm. However, there is more variation in length:

Standard Length x width (in mm)
M.2 2230 30 x 22
M.2 2242 42 x 22
M.2 2260 60 x 22
M.2 2280 80 x 22
M.2 2210 110 x 22

The thickness of M.2 hardware is not specified. Especially powerful M.2 SSDs like the Corsair MP600 rely on heatsinks, which can greatly increase the thickness of the module and, under certain circumstances, interfere with graphics cards or mainboard trays.

Most M.2 SSDs rely on M.2 2280, but there are exceptions. For example, the Kioxia BG4 only uses the M.2 2230 standard.

M.2 WLAN modules, on the other hand, mostly use the M.2-2230 standard.

Intel AX200
One M.2 WLAN card | Image: Equippr

But not every M.2 module can be inserted into every M.2 slot. This is where the so-called “key”, the specification of the connector, plays a role. The most common keys are:

Key name Pins Connection Frequent use with
A-Key 8-15 PCIe x2 / USB WLAN cards
E-Key 24-31 PCIe x2 / USB WLAN cards
M-Key 59-66 PCIe x2 or x4 PCIe-SSDs
B-Key 12-19 SATA SATA SSDs
B-M-Key 12-19 & 59-66 SATA / PCIe x2 or x4 SATA or PCIe SSDs

If you want to use an SSD with the highest possible sequential read and write rates, you should use an M-Key SSD. These use the NVMe protocol and are therefore often referred to as “NVMe SSDs”.

B-Key SSDs, which are connected via SATA and use AHCI as protocol, do not offer any speed advantage over fast 2.5-inch SSDs. On the contrary, under certain circumstances the warm exhaust air from the graphics card can cause the M.2 SSD to heat up and have to throttle down. By the way, this behavior is commonplace with NVMe SSDs; this is due to the fast read and write rates combined with small physical size.

A special form of the M.2 slot is ASUS’ “DIMM.2”, which is part of Bo(a)rd in some of the manufacturer’s high-end models. This is basically a riser card that is inserted into a slot next to the RAM slots. One or more M.2 slots are located on the riser.

One ASUS DIMM.2 module

Of course, there are also risers that are designed for normal PCIe slots. They offer space for one or several M.2 SSDs.

What can the M.2 slot be used for?

Besides SSDs, the M.2 slot is most commonly used for WLAN cards, especially in notebooks. Here, the more compact form and lower weight of M.2 SSDs pay off compared to a regular 2.5-inch SSD. But the compact memory is also increasingly finding its way into desktop PCs. Since consumer hardware generally does not have any U.2 connections and PCIe slots are scarce, especially on inexpensive motherboards, M.2 SSDs connected via PCIe offer a good way of installing very fast flash memory.

How is M.2 hardware mounted?

The M.2 hardware is first inserted into the slot at an angle, then it is carefully pushed down. Finally, a 3 mm long screw with M2 thread is screwed into the spacer, which must first be fixed in the correct hole, of the M.2 slot.

Depending on the mainboard, however, it may happen that one or more SATA ports are switched off when one of the M.2 slots is occupied. It is best to consult the manual of your mainboard before buying an M.2 SSD to avoid unpleasant surprises.

M.2 screw
One M.2 screw with spacer. | Image: ssdscrews.co.uk
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Simon Lüthje

I am co-founder of this blog and am very interested in everything that has to do with technology, but I also like to play games. I was born in Hamburg, but now I live in Berlin.

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