Question Understanding PCIE slots/speeds

ellsswhere

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Jan 14, 2010
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With the prices of drives plummeting and new generations of NVME drives just around the corner I noticed I could double my storage for the same price I paid a year ago. However I am confused on the speed cap I should expect from my available PCIE slot.

My board (GA-AB350M-Gaming 3) has a single Gen3 x4 NVME slot which currently houses a 256GB Samsung 960 EVO. I was looking to purchase a 512GB HP EX920 to expand my storage however with a 1070 taking up the PCIE X16 slot there is only one slot left. Per Gigabyte's site the second slot is"...PCI Express x16 slot, running at x4 (PCIEX4) (The PCIEX4 slot conforms to PCI Express 2.0 standard.)"

This is where I become confused. If I am reading that correctly the remaining X16 slot is actually only a PCIEX4 Gen2 ... which if my other research is correct is 4 lanes running at 500mbps (2000mbps)... so an nvme drive capable of 3200mbps reads would be stuck at 2k.
Is this correct? Also are those numbers mainly theoretical and real world speeds don't even come close to that in day to day use? The reason I am even looking at NVME drives is the EX920 is $75 and an equivalent 860 EVO SSD is $77. I am sure I will get a board with 2 Gen3 NVME slots one day but I don't want to waste my money atm if I can achieve 'good enough speeds' considering the next fastest options are 500mbps ssds. As a note, I already have a 2TB HDD so this is mainly to gain space for Page files/Games.
 
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ellsswhere

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The B350 boards don't support 2 graphics cards so it doesn't split the gen3 16x. I believe the CPU supplies 20 gen3 pcie lanes. 16 to the GPU and 4 to the nvme drive. The gen2 pcie lanes are supplied by the mobo chipset. From what have have gathered they will not interfere with one another. Any nvme adapted to fit the remaining pcie lanes will just be bottlenecked.

Thanks for the help.
 

karenjoly

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Apr 13, 2018
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The two drives you mention do not occupy "expansion slots", they fill storage slots, in this board, an M 2 socket of which that board has one. An M2 connection to the chipset is normally properly described by the pcie generation and # of lanes, like so, pcie3 x4. The board you have just fudges that description, saying

1 x M.2 connector (Socket 3, M key, type 2242/2260/2280/22110 SATA and PCIe x4*/x2 SSD support)
* Actual support may vary by CPU.

without specifying the generation ! Very cheap or uninformed.

Concerning the expansion slot, your understanding of pciex4 is correct but the slot is properly described as pcie 2 x 4


When you say

I am sure I will get a board with 2 Gen3 NVME slots one day

you mean a board with x M2 slots, liked I have I might say (z390 chipset.).

Your dilemna is whether to buy an M2 pcie3x4 drive or not and now the answer is clear--you have nowhere to put it unless you buy an adapter to go in that expansion slot which we just figured is less than a perfect match but which will still give 2 GB transfers , considerably quicker than another sata drive will provide.

Anything else ?
 
This is where I become confused. If I am reading that correctly the remaining X16 slot is actually only a PCIEX4 Gen2 ... which if my other research is correct is 4 lanes running at 500mbps (2000mbps)... so an nvme drive capable of 3200mbps reads would be stuck at 2k.
Is this correct? Also are those numbers mainly theoretical and real world speeds don't even come close to that in day to day use?
Yes, you have it right. And no, you'd probably never hit 2000+ MB/s during normal use even if it was PCIe 3.0. If the NVMe drive is the same price as SATA drives, I guess you might as well get it. Although you have to consider the cost of the PCIe to M.2 adapter.
 

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