Question NVMe SSD Gen 4 on PCIe 3.0 x8

[hugope]

https://imgur.com/a/3SfUkdJ

View: https://imgur.com/a/3SfUkdJ


The previous picture is from the manual of the motherboard I have. It says I can put a Hyper M.2 X16 card on my motherboard and then I can attach NVMe SSDs to that card. I want to buy a PCIe Gen 4 NVMe SSD x4 and attach it to the PCIe Gen 3 x8 slot, and then add another 2 NVMe SSDs on the x4 slots. My question is, will the NVMe SSD that is in the PCIe Gen 3 x8 slot run as fast as it would, if it was on a PCIe Gen 4 x4 slot?

 

[CountMike]

https://imgur.com/a/3SfUkdJ

View: https://imgur.com/a/3SfUkdJ


The previous picture is from the manual of the motherboard I have. It says I can put a Hyper M.2 X16 card on my motherboard and then I can attach NVMe SSDs to that card. I want to buy a PCIe Gen 4 NVMe SSD x4 and attach it to the PCIe Gen 3 x8 slot, and then add another 2 NVMe SSDs on the x4 slots. My question is, will the NVMe SSD that is in the PCIe Gen 3 x8 slot run as fast as it would, if it was on a PCIe Gen 4 x4 slot?

No, gen3 will be approximately half speed of gen4 even in PCIe gen4 slot. Full NVMe is PCIe x4 of any generation, Two NVMe drives need PCIe x8 adapter of any generation.
So. PCIe x4 gen4 will run at gen3 speed if connected to PCIe gen3 slot, doesn't matter if in dedicated M.2 on the MB slot or PCIe adapter.

 

[Aeacus]

My question is, will the NVMe SSD that is in the PCIe Gen 3 x8 slot run as fast as it would, if it was on a PCIe Gen 4 x4 slot?

No.

While PCI-E 3.0 x8 slot has same bandwidth as PCI-E 4.0 x4, the issue is with M.2 drive itself. All M.2 drives are only x4 (four lane PCI-E), so, using PCI-E 4.0 M.2 drive in PCI-E 3.0 x4 slot, will still have the PCI-E 3.0 x4 speeds.

 

[hugope]

No

No.

Hi, thank you for your answers.

Then, what is the purpose of that feature? Why does it exist? Why does the feature of having a NVMe SSD on a PCIe 3.0 x8 exists?

 

[Aeacus]

Why does the feature of having a NVMe SSD on a PCIe 3.0 x8 exists?

It exists so that people can add more M.2 PCI-E drives to their system, compared to what is otherwise possible.

Normal MoBo has 2x M.2 slots. Some have 1x. Top-end ones can have up to 4x. So, when you have populated all M.2 slots and need more drives to use, you can use the PCI-E add-on card, to add more drives.

 

[Zerk2012]

https://imgur.com/a/3SfUkdJ

View: https://imgur.com/a/3SfUkdJ


The previous picture is from the manual of the motherboard I have. It says I can put a Hyper M.2 X16 card on my motherboard and then I can attach NVMe SSDs to that card. I want to buy a PCIe Gen 4 NVMe SSD x4 and attach it to the PCIe Gen 3 x8 slot, and then add another 2 NVMe SSDs on the x4 slots. My question is, will the NVMe SSD that is in the PCIe Gen 3 x8 slot run as fast as it would, if it was on a PCIe Gen 4 x4 slot?

What motherboard?
Depending on what your using the M.2 drive for you would probably never know the difference unless you were just running benchmarks.

 

[CountMike]

Hi, thank you for your answers.

Then, what is the purpose of that feature? Why does it exist? Why does the feature of having a NVMe SSD on a PCIe 3.0 x8 exists?

PCIe has gone thru several versions, each one doubling the throughput of one before. For all practical purposes, NVMe SDD started with PCIe gen3, now gen4 and gen5 prevail while gen6 is already standardized but not implemented. NVME is protocol for implementation of PCIe on SSD drives connected by M.2 socket format.
Adapters for M.2 sockets to PCIe sockets are generation neutral and could be used forany PCIe generation to any M,2 NVMe SSD. generation, Why x8 ? Because for full throughput of NVMe drive it requires 4 PCIe lanes so adapter has to provide 8 lanes from MB's PCIe bus/slot to feed 2 NVMe drives at full speed.

 

[hugope]

My motherboard is Asus Prime Z370-a

Sorry, I'm not following.
The manual says that if I put a Hyper M.2 X16 card on the socket PCIe 3.0 x16_1 socket, I'll be able to put at most 3 NVMe SSDs, not 4. The manual also says, two of them will be PCIe 3.0 x4 and one of them will be PCIe 3.0 x8. What I don't understand is why one of them will be PCIe 3.0 x8 if it has no use. Could someone please explain this to me?

 

[Eximo]

I believe they are referencing the CPUs bifurcation capabilities. "On CPU support"

The CPU has 16 lanes to the main PCIe slot. It is capable of doing 16x or 8x/8x. or 8x + 4x +4x.

It is more clear in the main specs page:

That first line is the CPU connected slots, the ones with the metal reinforcement.

2 x PCIe 3.0/2.0 x16 (x16, x8/x8, x8/x4+x4*, x8+x4+x4/x0**) *
1 x PCIe 3.0/2.0 x16 (max at x4 mode)
4 x PCIe 3.0/2.0 x1
* For 2 SSD on CPU support, install a Hyper M.2 X16 card (sold separately) into the PCIeX16_2 slot, enable this card under BIOS settings.
** For 3 SSD on CPU support, install a Hyper M.2 X16 card (sold separately) into the PCIeX16_1 slot, enable this card under BIOS settings.

8x/8x is intended for SLI, which your board still supports.

If you have a GPU in the first slot, you can do 8x to the GPU, and then 4x and 4x to a pair of SSDs in the HyperM.2 card.

If you install the Hyper M.2 card in the primary PCIe slot, you can have 3 SSDs, but then no video card.

You can't have 4 SSDs because they didn't set up the CPU to do 4 way bifurcation.

 

[Aeacus]

The manual says that if I put a Hyper M.2 X16 card on the socket PCIe 3.0 x16_1 socket, I'll be able to put at most 3 NVMe SSDs, not 4. The manual also says, two of them will be PCIe 3.0 x4 and one of them will be PCIe 3.0 x8. What I don't understand is why one of them will be PCIe 3.0 x8 if it has no use.

Basically, Eximo already explained it. But here is a bit more that i wanted to add;

First off, some specs;
MoBo: https://www.asus.com/motherboards-components/motherboards/prime/prime-z370-a/techspec/
Hyper M.2 X16 Card: https://www.asus.com/motherboards-components/motherboards/accessories/hyper-m-2-x16-card/techspec/

And perhaps the most important one: "Compatibility of PCIE bifurcation between Hyper M.2 series Cards and Add-On Graphic Cards",
link: https://www.asus.com/support/faq/1037507/

If you look at that FAQ link, you'll see that for many Asus MoBos with Intel chipset, PCI-E bifurcation, while using x8 + x4 + x4, is only allowing 3x M.2 drives, and not 4x, per one PCI-E x16 slot.