Perhaps you have an older PCIe 3.0 SSD drive and are upgrading to a motherboard with PCIe 4.0 M.2 slots. Or maybe you want to buy a lower-cost PCIe 3.0 SSD for your existing motherboard with PCIe 4.0 slots.
Let's dig into whether this will be compatible.
Can I Use a PCIe 3.0 NVMe SSD in a PCIe 4.0 M.2 Motherboard Slot?
A PCIe 3.0 NVMe SSD will work in a PCIe 4.0 M.2 motherboard slot at PCIe 3.0 speeds.
PCI-Express
versions are backward and forward compatible, meaning that you can use a PCIe 3.0 storage device in 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 from 4.0 to 3.0 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.
| 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.
Samsung 980 PRO SSD with Heatsink 1 TB PCIe Gen 4 NVMe M.2
Check Price on Amazon
Amazon Affiliate Link
How Much Slower Would a PCIe 3.0 SSD Be in a PCIe 4.0 Slot?
A PCIe 3.0 SSD would not be any slower in a PCIe 4.0 slot because its maximum speed is that of PCIe 3.0. PCIe 3.0 M.2 SSDs cannot go any faster than PCIe 3.0 speeds.
On the other hand, you could improve the performance by upgrading to a PCIe 4.0 SSD and a motherboard with PCIe 4.0 M.2 slots.
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.
A PCIe 3.0 M.2 SSD, on the other hand, would have a maximum potential speed of 4000 MB/s.
Our Favorite M.2 NVMe SSDs
Best PCIe 4.0 M.2 SSD: Samsung 980 PRO SSD
- 1 TB Capacity
- Read speeds up to 7000 MB/s
- To avoid throttling, this M.2 SSD works best with a heatsink, which this version comes with
- I've had many great experiences with Samsung SSD reliability!
- Compatible with Playstation 5
Samsung 980 PRO SSD with Heatsink 1 TB PCIe Gen 4 NVMe M.2 Check Price on Amazon Amazon Affiliate Link
Best Value M.2 SSD: Samsung 970 EVO Plus SSD
- If you're more interested in cost than achieving the fastest speeds, this is a great value!
- 1 TB Capacity
- Read speeds up to 3500 MB/s
- I've had many great experiences with Samsung SSD reliability!
Samsung 970 EVO Plus 1 TB SSD Check Price on Amazon Amazon Affiliate Link
M.2 Keying
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?
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
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/
Other Considerations When Building a PC
Want to brush up on other new technologies to consider when building a computer? Check out these articles:
- Cases:
- CPUs:
- The Best CPUs for Gaming
- Which Intel and AMD CPUs Support PCIe 5.0?
- Which Intel and AMD CPUs Support PCIe 4.0?
- LGA 1700 CPU List
- LGA 1200 CPU List
- Look up an Intel or AMD CPU on TechReviewer for related recommendations:
- The Best CPUs for Gaming
- CPU Coolers:
- Storage:
- Memory:
- PCI-Express:
- Motherboards:
- Graphics Cards:
- Power Supplies:
- Keyboards:
- Monitors:
Learn More About PCI-Express
Want to brush up on the latest PCIe products, versions, and features? Check out the articles in this PCI-Express series:
- What is PCIe?, What is PCIe 5.0?, and What is PCIe 4.0?
- Is PCIe 5.0 Worth It? and Is PCIe 4.0 Worth It?
- Which Intel and AMD CPUs Support PCIe 5.0?
- Which Intel and AMD CPUs Support PCIe 4.0?
- Which Motherboards Support PCIe 5.0?
- Which Graphics Cards Support PCIe 4.0?
- How Fast is PCIe 5.0? and How Fast is PCIe 4.0?
- Is PCIe Backward Compatible?
- Can I Put a PCIe x4 or x8 Card in an x16 Slot?
- Can I Use a PCIe 4.0 NVMe SSD in a PCIe 3.0 Motherboard Slot?
- Can I Use a PCIe 3.0 NVMe SSD in a PCIe 4.0 Motherboard Slot?
- Can I Use a PCIe 4.0 Graphics Card in a PCIe 3.0 Slot?
- Can I Use a PCIe 3.0 Graphics Card in a PCIe 4.0 Slot?
- What is the Latest Version of PCIe?
- PCI vs. AGP vs. PCIe? Time to Upgrade!
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