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PCIe Slot Utilization

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  • Asus
  • GPUs
  • Storage
  • Components
  • Motherboards
Last response: in Components
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September 29, 2014 9:09:28 AM

Hi,

I'm planning to purchase an ASUS Z97-I Plus motherboard, which has 1 PCIe expansion slot. I'd like to use this slot for a GPU (EVGA GTX 750 Ti), and was recently considering purchasing an M.2 drive, which the motherboard also supports. However, I just read that an M.2 drive, while having its own socket, actually connects to the system through the PCIe bus (if it's to maximize its capabilities beyond SATA capabilities). If this is the case, does this mean that I would need a motherboard with more than one PCIe interface in order to support both the GPU and the M.2 drive?

Thanks a lot for any help!

More about : pcie slot utilization

September 29, 2014 9:27:33 AM

Your ASUS Z97-I Plus has an M.2 socket 3 and the for mentioned PCIe expansion slot. You do not need a motherboard with more than one PCIe slot. The lanes for PCI-e are shared between the PCIe socket and M2 socket. The limitation is the number of lane available for the CPU.
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September 29, 2014 11:15:09 AM

It's located on the bottom side of the Z97I-PLUS motherboard:

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September 30, 2014 12:12:41 PM

So the GPU and the M.2 drive can "share" the same PCIe slot?
And how can I check if the number of lanes suffice?
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September 30, 2014 12:21:24 PM

4mylgl6 said:
So the GPU and the M.2 drive can "share" the same PCIe slot?
And how can I check if the number of lanes suffice?

The GPU and M.2 do not share lanes on this board. The M.2 slot is wired into two of the four PCIe 2.0 lanes supplied by the Z97 chipset, and not any of the PCIe 3.0 lanes supplied by the CPU. If you use the M.2 slot, your GPU will still have access to the full 16 PCIe 3.0 lanes provided by the CPU.
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September 30, 2014 1:27:00 PM

It's a mini ITX board though... It has no PCIe 2.0 slots. Just one single PCIe 3.0 x16 slot.
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September 30, 2014 3:15:16 PM

4mylgl6 said:
It's a mini ITX board though... It has no PCIe 2.0 slots. Just one single PCIe 3.0 x16 slot.

I know. When I say "PCIe 2.0" I'm referring to the interface used by the M.2 slot, not to any physical PCIe 2.0 slot on the motherboard (as obviously the board doesn't have any).

The CPU is equipped with 16 PCIe 3.0 lanes. These are the ones that are wired to the single x16 PCIe slot on the ASUS Z97I-plus board. The Z97 chipset has its own supply of PCIe 2.0 lanes that are normally used to provide further connectivity for a board, for instance they are often wired up to provide x1 PCIe slots on a motherboard, or are wired up to any additional third party controllers that are present (like an additional SATA controller for instance).

As you already know, the ASUS mini ITX board you're talking about has no x1 PCIe slots, it just has a single x16 PCIe slot, that is wired directly into the PCIe lanes coming from the CPU. The lanes from the CPU are only used for this one purpose. So, to provide the M.2 slot, without taking any PCIe lanes away from the x16 slot you use for your graphics card, ASUS takes two of the PCIe 2.0 lanes that the Z97 chipset is equipped with, and uses those to wire in the M.2 slot.

So in summary, the M.2 slot and the x16 slot you use for the graphics card are completely separate, and will not influence each other in any way. You can use both slots without any issue.
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September 30, 2014 3:56:31 PM

Thanks for the detailed answer, I appreciate your help!
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September 30, 2014 4:55:56 PM

No worries, glad to help :) 
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