How Many PCIe Lanes Does M.2 Slot Use?

Mehak Sohail | Last Updated On December 12th, 2021

If you’re looking to build a computer or upgrade your existing one, you may be wondering about how many PCIe lanes does M.2 slot use and if your computer build offers SSD support.

NVMe SSDs with an M.2 slot use a maximum of 4 PCIe lanes. However, the exact lanes needed depend on the specifications of your unique component and how your motherboard is configured. PCIe lanes offer exponentially faster read speeds than SATA ports and are ideal for SSD use. 

M.2 slots are an interface that’s widely used for lighting quick SSD cards. Compared to the older generation M.2 SATA SSD cards, M.2 NVMe SSDs utilize PCIe lanes.

Furthermore, NVMe SSDs come in a smaller form factor which takes up less space inside your computer.

However, the exact amount of PCIe lanes on the M.2 slot and its PCIe version dictate the performance it offers.

So, I’ll discuss everything you need to know about M.2 slots and PCIe lanes in this in-depth guide today.

PCIe Lanes Explained

Before diving into the M.2 slot specifications, it’s essential to go over PCIe lanes.

This is because the number of PCIe lanes directly impacts the slot’s overall speed and throughput rate.

Furthermore, the exact version of the PCIe slot affects how fast the slot performs.

So, a PCIe 4.0 slot with 16 lanes would have a significantly higher throughput rate than a PCIe 2.0 (see also PCIe 2.0 vs 3.0) slot with two lanes.

In fact, every newer generation of PCIe doubles its transfer speed in relation to the previous generation.

Here’s a summary of PCIe versions and lanes, along with their throughput rates.

Version x1 (GB/s) x2 (GB/s) x4 (GB/s) x8 (GB/s) x16 (GB/s)
1.0 0.250 0.500 1.000 1.969 4.000
2.0 0.500 1.000 1.969 4.000 8.000
3.0 0.985 1.969 3.938 7.877 15.754
4.0 1.969 3.938 7.877 15.754 31.508
5.0 3.938 7.877 15.754 31.508 63.015

The denotation x1, x2, x4, etc. indicates how many lanes are on that PCIe slot. For instance, an x1 PCIe slot has one lane while an x16 PCIe slot has 16 lanes.

Let’s discuss a few critical points about SSDs and their throughput rates:

  • SATA 3 slots have a max speed of 0.75 GB/s. So, an M.2 SATA slot has a max potential throughput speed of 0.75 GB/s.
  • PCIe 4.0 lanes offer a throughput rate of 1.969 GB/s each.

PCIe 4.0 M.2 NVMe slots with four lanes have a theoretical max throughput rate of 7.877 GB/s

  • PCIe 4.0 M.2 NVMe slots with two lanes have a theoretical max throughput rate of 3.938 GB/s
  • PCIe 3.0 M.2 NVMe slots with four lanes have a theoretical max throughput rate of 3.938 GB/s
  • PCIe 3.0 M.2 NVMe slots with two lanes have a theoretical max throughput rate of 1.969 GB/s

However, it’s important to know that SSDs usually don’t reach the theoretical max throughput rate.

We also have an article here about what can be plugged into PCIe slots which you might be interested in.

How Many PCIe Lanes Does M.2 Slot Use

Hard disk SSD m2 on the motherboard background. Hard disk SSD m2 on the motherboard background. M2 technology can develop the speed of reading and writing information up to 3500 mbs.

As I mentioned before, the maximum amount of lanes an M.2 slot uses is four or an x4 slot. M.2 slots using 4 PCIe lanes support the fastest NVMe SSDs available on the market today.

However, your motherboard may only offer M.2 slots with x2 PCIe lanes. If this is the case, NVMe SSDs requiring an x4 PCIe lane with be bottlenecked with only have half of the throughput needed for optimal performance.

So, let discuss how different configurations of motherboards affect M.2 slots.

Motherboard Chipsets and M.2 Slots

Your specific motherboard’s chipset will determine the configuration of the M.2 slot. For example, the M.2 slot could be using the PCIe lanes of the CPU or connected to the motherboard chipset lanes instead.

If the motherboard has two M.2 slots, it could use a combination of CPU lanes and motherboard chipset lanes.

For example, a B550 motherboard can be used in different ways:

  • One M.2 slot equipped with four PCIe lanes
  • Two M.2 SATA slots and one NVMe SSD slot with two PCIe lanes
  • Two NVMe SSD slots with two PCIe lanes

However, most PC users will go with the first option with one M.2 slot using an x4 PCIe slot.

In conclusion, the PCIe lanes used by an M.2 slot depend on how your motherboard is configured.

How PCIe Versions Impact SSD Performance

m.2 replaces the mSATA standard, which uses the PCI Express Mini Card physical card layout and connectors.

As you saw earlier in the table above, differing PCIe lane sizes offer different transfer speeds. The PCIe generation featured on your motherboard will determine how fast your SSD can run.

For example, the 4th generation Samsung 980 Pro NVMe SSD requires a PCIe 4.0 slot with four lanes. This specific SSD card can potentially reach up to 7.0 GB/s.

Alternatively, the 3rd generation Samsung 970 Pro NVMe SSD has a max read speed of 3.5 GB/s and requires 4 PCIe 3.0 lanes.

So, using a newer generation SSD with an older generation PCIe slot reduces the card’s performance.

PCIe Version and CPU

Another vital thing to know is that different CPUs support different PCIe versions. This means that your CPU and the PCIe version it supports directly affect your SSD speeds as well.

In essence, installing a 4th generation PCIe NVMe SSD while using a PCIe 3.0 processor will bottleneck your SSD card significantly.

PCIe Version and Motherboard Chipset

Furthermore, the chipset on a computer’s motherboard will determine the PCIe version of a specific M.2 slot.

For instance, let’s discuss the B550 chipset. On the B550, the motherboard chipset lanes only conform to PCI 3.0, while the CPU lanes conform to PCIe 4.0.

For this reason, a CPU connected M.2 slot would be compatible with NVMe SSDs using PCIe 4.0.

On the other hand, the motherboard chipset connected M.2 slot would be optimal with PCIe 3.0 NVMe SSDs.

Now, let’s take discuss an x570 chipset and how it differs from a B550 chipset.

Motherboards with an x570 chipset use M.2 slots that conform to PCIe 4.0. Both the motherboard and CPU chipset allows you to equip a 4th generation NVMe SSD and run it at its full potential.

In summary, both the CPU and chipset are important when determining how many PCIe lanes an M.2 slot uses and which PCIe version it’s optimal with.

Does the PCIe Version Impact the Number of Lanes for an M.2 Slot?

If you’re using a PCIe 3.0 NVMe SSD that uses four PCIe 3.0 lanes, it can theoretically perform the same if installed on a PCIe 4.0 x2 slot.

So, you can mix and match SSDs and PCIe slots if the required throughput rate is reached.

Conclusion

It’s essential to examine your motherboard’s specifications when deciding which SSD card to purchase. Then, you can understand what sized SSDs you can use, the PCIe version your motherboard supports, and the chipset it features.

However, to answer the main question of this guide, M.2 slots use a maximum of four PCIe lanes.

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