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Can I Use a PCIe 4.0 NVMe SSD in a PCIe 3.0 Motherboard Slot?

Learn whether PCIe 4.0 NVMe M.2 SSDs will work in PCIe 3.0 M.2 motherboard slots.

Samsung 970 EVO SSD M.2 NVMe Kevin Jones / TechReviewer

Last Updated: August 30, 2022

Written by Kevin Jones

Can I Use a PCIe 4.0 NVMe SSD in a PCIe 3.0 M.2 Motherboard Slot?

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A PCIe 4.0 NVMe SSD will work in a PCIe 3.0 M.2 motherboard slot at PCIe 3.0 speeds.

PCI-Express versions are backward compatible, meaning that you can use a PCIe 4.0 graphics card or storage device on a PCIe 3.0 or PCIe 2.0 system. However, PCI-Express will use speeds based on the lowest of the two versions for communication. For example, if you use a PCIe 3.0 NVMe SSD with a PCIe 4.0 system, the SSD would be running at PCIe 3.0 speeds.

Reducing the PCIe version would halve the max potential bandwidth. However, you may not experience a performance impact if your device is not using the available bandwidth.

You can refer to the following table to determine the bandwidth limit and decide whether that is adequate for your needs.

PCI-Express Speeds (Rounded)
x1 Bandwidth x2 Bandwidth x4 Bandwidth x8 Bandwidth x16 Bandwidth
PCIe 1.0 250 MB/s 500 MB/s 750 MB/s 2 GB/s 4 GB/s
PCIe 2.0 500 MB/s 1000 MB/s 2 GB/s 4 GB/s 8 GB/s
PCIe 3.0 1 GB/s 2 GB/s 4 GB/s 8 GB/s 16 GB/s
PCIe 4.0 2 GB/s 4 GB/s 8 GB/s 16 GB/s 32 GB/s
PCIe 5.0 4 GB/s 8 GB/s 16 GB/s 32 GB/s 63 GB/s
PCIe 6.0 8 GB/s 16 GB/s 32 GB/s 63 GB/s 126 GB/s

Check out my recommended M.2 SSDs below.

How Much Slower Would a PCIe 4.0 SSD Be in a PCIe 3.0 Slot?

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Let's consider Samsung's 1 TB 980 PRO PCIe 4.0 NVMe M.2 SSD as an example.

This SSD has a max read speed of 7000 MB/s, only achievable in a PCIe 4.0 x4 slot.

In a port with only two PCIe 4.0 lanes (x2), this SSD would be limited to 4000 MB/s. In a port with only two PCIe 3.0 lanes (x2), this SSD would be limited to 2000 MB/s. In a port with four PCIe 3.0 lanes (x4), this SSD would be limited to 4000 MB/s.

Our Favorite M.2 NVMe SSDs

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Best PCIe 4.0 M.2 SSD: Samsung 980 PRO SSD

Best Value M.2 SSD: Samsung 970 EVO Plus SSD

M.2 Keying

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M.2 connectors are keyed in different ways to ensure compatibility and indicate supported interfaces. Connectors with different keyings are physically unable to be connected. M.2 SSDs typically use one of three common keyings: B, M, or B+M. PCIe 4.0 SSDs will always have an M keying.

  • NVMe M.2 ports with a B keying indicate that the system will provide 2 lanes of PCI-Express bandwidth.
  • NVMe M.2 ports with an M keying indicate that the system will provide 4 lanes of PCI-Express bandwidth.
  • NVMe M.2 ports with a B+M keying maximize compatibility but only provide 2 lines of PCI-Express bandwidth.

Are PCIe Versions Forward Compatible?

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PCIe versions are forward compatible, meaning that you can use a newer PCIe device with an older system. However, PCI-Express will use speeds based on the lowest of the two versions for communication.

Check out the table above to determine what the throughput limit would be for a specific configuration.

Multiple PCIe Versions for CPU/Motherboard

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Some CPUs and motherboards provide PCI-Express lanes at multiple PCIe versions. In these cases, you can choose which devices need the most bandwidth to decide which should be connected to the highest version PCIe lanes. While laying out your system, keep in mind that PCIe speeds will be based on the lowest PCIe version between the slot/port and the device.

Other Considerations When Building a PC

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Want to brush up on other new technologies to consider when building a computer? Check out these articles:

Learn More About PCI-Express

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Want to brush up on the latest PCIe products, versions, and features? Check out the articles in this PCI-Express series: