I am reading the specs of an MSI mb http://us.msi.com/product/mb/H97MG43.html#hero-specification.

  • 1 x PCIe 3.0 x16 slot (PCI_E1, supports x16 speed)
  • 1 x PCIe 2.0 x16 slot (PCI_E4, supports x4 speed)

  • 2 x PCIe 2.0 x1 slots**
    ** Two PCIe x1 slots can not be used simultaneously. When installing an expansion card in one of pcie 2.0 x1 slots, another slot will be unavailable.

Notice that it says only one PCIe 2.0 x1 slot is available at any one time.

Does it mean ... ?

  1. You should stick only one pcie x1 card on the mobo, and therefore you have to choose one of the two slots, to stick that card in.


  1. You can have both slots occupied with a card each. Both cards will be operational, but their drivers must cooperate with the OS/BIOS to contend/negotiate to time-share the pcie x1 traffic.

If the answer is (1), why then provide two similar slots if only one is usable?

  • Good air circulation for the GPU heatsink typically would be blocked by the use of the adjacent slot, so optimally you would not bother to use that adjacent slot. So #1. But it does seem like a cost-cutting measure. – sawdust Nov 28 '14 at 20:04
  • If you notice the mobo schematics, the two pciex1 slots are sandwiched in between two pciex16 slots. Both pciex16 are usable simultaneously. – Blessed Geek Nov 28 '14 at 22:41
  • "If you notice the mobo schematics" -- Don't you mean "photo"? Mobo manufacturers haven't released schematics since the days of the original IBM PC. Don't use words that you don't know the (proper) meaning of. "Both pciex16 are usable simultaneously" -- Okay, so what?. The GPU I'm referring to would typically be installed in the PCIex16 that is closest to the CPU. That card would (physcially) restrict use of the adjacent PCIex1 slot. – sawdust Nov 29 '14 at 0:03
  • Your question, as worded, can appear to be primarily opinion-based. It may be better if you reworded it to be more objective in tone, so it doesn't get closed by mistake. Your question has merit and we don't want that to happen. – bwDraco Nov 30 '14 at 0:10

The answer is #1.

The reason that there are two slots is to accommodate large expansion cards that may take up more then one slot. Typically this is video cards.

They used to just leave an empty space beneath the pci express x16 slot, but then they started releasing cards that took up three slots. And then everything got complicated with SLI and Crossfire using multiple pcix slots.

Essentially, it's there to accommodate many different arrangements of high end video setups.

It's worth noting that pcix is backwards compatible, and you can stick a 1x card into a 16x slot without an issue - even though the connector is way shorter.

  • I don't know of any graphic/video card that would use one one PCI lane. You understood the question wrongly. I am asking why have two PCIEx1 slots? Not about PCIEx16 slots. – Blessed Geek Nov 28 '14 at 22:37
  • you clearly did not read my answer. – Arthur Dec 22 '14 at 16:12

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