Before starting, I would like to highlight that the M.2 NVMe drives transfer the data through the PCIe lanes on our motherboard.
So, if we talk about compatibility, all the PCIe versions are backward and forward compatible. In other words, If you are using a PCIe 4.0 or 5.0 motherboard/CPU, you can use a PCIe 3.0 NVMe SSD on it.
For example, your system is running on a Ryzen 1st or 2nd generation CPU or Intel’s 8th, 9th, or 10th generation CPU. In this case, your motherboard is a PCIe 3.0 motherboard. We can consider PCIe 2.0 motherboards here as well but they are rare to see nowadays.
So, on these motherboards, if you install PCIe 4.0 SSDs such as Samsung 980 Pro, WD Black SN850, or Crucial P5 Plus, they will get installed and do their job perfectly fine. But, there will be a performance bottleneck which we are going to discuss below. Know more about the PCIe interface here.
Can you install a PCIe 4.0 SSD on a PCIe 3.0 motherboard slot?
The form factor of both PCIe 4.0 and PCIe 3.0 NVMe SSDs is the same i.e. M.2. So, if you install a PCIe 4.0 SSD on a PCIe 3.0 motherboard slot or vice-versa, it will get installed without any issues. The software will also recognize it and you can use it just like your normal storage drive.
Also Read: Difference between Gen 3 and Gen 4 SSDs?
Will it bottleneck the Gen 4 NVMe speed?
Yes. There is going to be a serious bottleneck here. Let me explain why. First of all, look at the table below.
|PCIe Version||x1 Bandwidth||x2 Bandwidth||x4 Bandwidth||x8 Bandwidth||x16 Bandwidth|
|1.0||250 MB/s||500 MB/s||1 GB/s||2 GB/s||4 GB/s|
|2.0||500 MB/s||1 GB/s||2 GB/s||4 GB/s||8 GB/s|
|3.0||985 MB/s||1.969 GB/s||3.938 GB/s||7.877 GB/s||15.754 GB/s|
|4.0||1.969 GB/s||3.938 GB/s||7.877 GB/s||15.754 GB/s||31.508 GB/s|
|5.0||3.938 GB/s||7.877 GB/s||15.754 GB/s||31.508 GB/s||63.015 GB/s|
|6.0 (Soon)||7.877 GB/s||15.754 GB/s||31.508 GB/s||63.015 GB/s||126 GB/s|
All NVMe SSDs use 4 PCIe lanes for the purpose of data transfer. So, if we see the bandwidth in 4 lanes of PCIe 3.0, it is around 4GB/s. But, the bandwidth for PCIe 4.0’s 4 lanes is around 8 GB/s.
Now, let’s say our Gen 4.0 or PCIe 4.0 SSD is coming with a theoretical read/write speed of 7000/6500 MB/s.
When you install it on a PCIe 3.0 motherboard and then it gets just 4 GB/s bandwidth, how can it reach its maximum potential? So, this is the bottleneck I am talking about.
What will be the maximum achievable read/write speed?
Whether we talk about the read or write speed, your Gen 4.0 NVMe SSD will never go beyond 4 GB/s while working on a PCIe 3.0 slot.
Should you buy a Gen 4 SSD for a Gen 3 motherboard?
If you are not planning to upgrade your system in the future where you might have a capable system with PCIe 4.0 support, you should not buy a Gen 4 SSD yet.
There could be a case where you might be having a Gen 4 SSD lying around and you are looking to utilize it instead of buying a new Gen 3 SSD. In that case, it is good to save your money.
But, going for a PCIe 4.0 specifically for a Gen 3 motherboard and CPU is a complete waste of money. I am saying it because Gen 4 SSDs are not cheap.
So, if you think you are not going to upgrade your system in upcoming years, just for a gen 3 SSD on your gen 3 system.
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