Newbie question on AMD motherboards and M2 ssd

Oct 11, 2018
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Hello,

I'm about to build a new PC based on an AMD ryzen 2700 and a B450 motherboard. I'm not planning to overclock. So, from what I have read a "MSI B450 gaming pro carbon ac" seems a good choice (even something cheaper would do it).
My question is something that I think it's clearly explained but: If I connect a ssd to the M2_2 slot , then PCI_E2, PCI_E3, PCI_E4 and PCI_E5 slots will be unavailable (as noted in the user manual).

Ok so it means that then there is no possibility to connect an PCI expansion card, like video capture, sound card, etc..., isn't it?

So, when using a M2 in such an slot using that chipset, it's better to go for a mATX form factor, as the extra PCI slots will be unabailable?

Am I correct or I'm missing something?

Thanks for your help.
 

androbourne

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Jul 18, 2017
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Hmm no that doesn't sound correct. Can I ask where you heard this from?

M.2 uses it own slot on the mobo and the PCI lanes are still usable... What you might be referencing too is that M.2 may use the PCI lane bus for speed (nvme m.2s). However, no where near capacity, so you can still use the PCI slots along with M.2 and never hit the capacity of PCI.

If you are going with a standard case then get a standard size full. Full ATX will work just fine.
 

shmoochie

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May 10, 2018
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Are you sure? His mobo specs show this: "PCI_E2, PCI_E3, PCI_E4 and PCI_E5 slots will be unavailable when installing M.2 PCIe SSD in M2_2 slot. SATA5 and SATA6 ports will be unavailable when installing a M.2 device in M2_1 slot."

I think it is a protocol to preserve pcie lanes instead of restricting to gpu to 3.0 x 8.

Edit: oh I just saw that he was asking about PCI and not PCIE. Yes, you can still add expansion cards to the PCI slots.
 

androbourne

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Jul 18, 2017
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Yes. Exactly what I thought when I first read it. But thats why I asked for his source.

Also read at the bottom of his image. It says when installing "M.2 PCIe SSD" sadly. It does not say if it is restricted to SATA M.2 or NVME drives. But I believe the results would be the same.

PCI slots should still work for his needs.
 
Oct 11, 2018
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Edit: oh I just saw that he was asking about PCI and not PCIE. Yes, you can still add expansion cards to the PCI slots
Oh !! I'm just thought that everything was the same (I called PCI, but thought today this is called PCIE)

The motherboard outline only shows PCI_E1, PCI_E2, PCI_E3, PCI_E4 and PCI_E5. And in that commented part, it is explained the point of M2_2 disabling PCI_E2 to PCI_E5)

Thanks.
 
That motherboard has two M.2 slots. M2_1 connects straight to the CPU (and can support either PCIe or SATA SSDs), and therefore does not share bandwidth with any other PCIe slots. So installing an SSD there would not affect the other PCIe slots. It will disable 2 SATA ports though.

M2_2 connects to the chipset (and can only support PCIe SSDs), and shares bandwidth with other PCIe slots. So PCIe slots 2 through 5 are disabled when an SSD is installed in M2_2.
 
Oct 11, 2018
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Ok, so thank you very much.

BTW, I think it's a bit confusing...

edited after reading the previous post from TJ Hooker... definitively this is not clear..
And of course, I was asking if using a M2 NVME device

Best regards.
 
There are only so many PCIe lanes available to wire up to the expansion slots and the M.2 slots. If you use an NVMe M.2 card, you will have to use PCIe lanes, taking them away from the listed PCIe slots. Simple as that.

If you use a SATA M.2, which is most likely what MSI means by the use of the term "SSD," you instead use the SATA interface, so you lose connectivity there. The SATA interface already has it's own PCIe lanes dedicated to it, so it does not effect PCIe connectivity.

When the manual says you will lose PCIe expansion slots under certain conditions, it means it.

Are you really planning to install 2 x M.2 devices? Also, if you're going to go with an SATA based M.2 SSD, you're not going to gain a whole lot except a smaller drive and less cabling. The same end result is still doable by just plugging into SATA ports at that point.
 

androbourne

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Jul 18, 2017
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Well both claims are correct.

I'm suggesting that PCI lane will still function but PCIe wouldn't as mentioned in the mobo spec sheet.

And as TJ suggested. You can just use the M.2 Slot#1 which wouldn't effect PCIe at all either. So if you are in need of extra PCIe lanes, then you can just use the M.2 Slot #1.

If you were to use M.2 Slot#2 then PCIe lanes become disabled, but any PCI lanes you have would still be functional.

From what is sounds like, you just have one M.2 drive, so just install it in M.2 Slot#1 and you shouldn't have any issues.

Hope that clears it up a bit.
 
Oct 11, 2018
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No, no both slots. My idea was to build a PC using these new ssd technologies NVME, that seems so crazy fast. But then I thought It makes no sense if I would like to use a PCIE slot in the future... That's why I asked. And I think my question was not a dummy question.

Thank you all for your helpful information !!!

 

That mobo doesn't have any PCI slots, only PCIe.
 

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