Question Are PCIe 4x16 available for graphic card if 2 x M.2 installed on the motherboard?

[Star2222]

Hi,
on my MSI MAG B550 TOMAHAWK Motherboard I already installed two M.2 SSD on the motherboard itself. But looking at the PCIe table in the manual (screenshot below) it is not clear - to me - if the PCIe E1 still has full PCI 4 x 16 lanes available?

Also why does PCI_E1 shows 3.0/4.0? What decides if it works as PCIe 3.0 or PCIe 4.0?

Sorry if these are stupid questions

And thank you for all help as always!

 

[Imperat0r]

Hello
As you can notice in the table you presented, if you are using both M2 slots, then you will have only 1 PCIe 4.0x16 available.
And that will be PCI_E1.
The only other PCI available will be PCI_E4 which is only 3.0x1
AND one more important thing : M2_2 will only support PCIe x2.

 

[Star2222]

Thank you @Imperat0r

What is the difference between PCIe x2 and x4, are they the PCIs lanes?

If so, does it then mean that my second M.2 drive (a WD_BLACK SN750 1TB High-Performance NVMe M.2NVMe) is actually running at half of its speed?

Thank you

 

[Imperat0r]

The difference between x2 and x4 is the speed you have for your PCIe because in 2x you use 2 lanes and in 4x you use 4 lanes.
As the motherboard manufacturer said, yes, when you use both M2 SSD's, the one inserted in M2_2 will work only in PCIe x2 mode.
In term of speed that won't be a disaster. M2 NVME already have a good speed compared to M2 SATA.

A single PCI-E 3.0 lane has a theoretical throughput of 8 GT/s (gigatransactions per second), which equals 985 MB/s. The x2 marking implies two lines, that is, speeds up to 1970 MB/s.

I believe you will be ok.

 

[Star2222]

Thank you @Imperat0r
I appreciate your explanation!

Just one small clarification. I appreciate that - like you said - they are so fast that in practice is not a a diaster because of the very high speeds, but specifically with my NVME's speed and my motherboard speed, would the effective transfer speed on the second M.2 be just a little less, maybe around 30% less or a full half speed?

I tried figuring it out with some google searches after your reply but didn't.

I am asking because launching large programs sometimes takes quite a bit so I know if it is worth upgrading the M.2 on the first slot?

If so, which M.2 SSD would you suggest to achieve maximum performance?

Thank you

 

[Math Geek]

i think you have misread the chart.

the second m.2 slot is 3.0 x 4. it only drops to x2 if you are ALSO using pcie 2 and 3 slots along with it.

the pcie 1 slot stays at 4.0 x 16 no matter what so that's not a concern.

your WD_BLACK SN750 is 3.0 x4 anyway so it will run full speed in the second m.2 slot so long as you leave the 2nd and 3rd pcie slot empty.

and your other question about pcie 1 slot being both 3.0 and 4.0 depends on the cpu installed. the 3000 and 5000 series cpu's support pcie 4.0 while the older 1000 and 2000 series only support 3.0. i believe some of the newer APU's also only support pcie 3.0.