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PCIe Lanes, M.2 x4 or x2

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  • Storage
  • Build
  • Motherboards
Last response: in Motherboards
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September 25, 2014 9:29:57 AM

Ok, so I'm upgrading out of my long standing AMD build and switching sides to Intel. I'm pretty set on Devil's Canyon (4790k) unless someone knows the release date for Broadwell...but CPU aside, my question lies strictly on the M.2 PCIe slot. The board I've tentatively decided on is the Z97-WS from Asus. My question is does the M.2 slot on this board come in x2 or x4? I also have a question in total lanes used. With any graphics card, will I be getting x16 or not? I'm really looking for an advanced level answer I guess. I know Haswell has 16 lanes and there are a few more lanes on the z97 chipset, so I just want an understanding of how many lanes I can get on the Z97-WS M.2 slot and how it will affect my GPU

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a b G Storage
a b V Motherboard
September 25, 2014 9:45:24 AM

The M.2 slot on the Z97-WS is wired to the chipset PCIe lanes (x2 at PCIe 2.0 transfer rates), so the lanes from the CPU will not be effected by the use of an M.2 device; you'll still have the full 16 PCIe 3.0 lanes available for graphics.
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September 25, 2014 10:05:29 AM

so it is x2. is there going to be much gain in the next year or two that would require x4? Say I want to put in the Samsung XP941 or in the future the SP941, am I missing a chunk of performance in those two lanes? Would it even work as a boot drive?
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a b G Storage
a b V Motherboard
September 25, 2014 11:09:15 AM

The XP941, as a x4 device, would certainly be constrained by an x2 M.2 slot, but really it's a question of perspective. It would still be extremely fast (faster than a SATA III based SSD) even over just two lanes, so it really comes down to usage scenario.

If you genuinely need extremely fast storage, for productivity reasons for example, then the loss in performance may not be acceptable (equally, if the idea of 'wasted' potential irks you, it may not be acceptable for that reason). But for the majority of users, the difference in speed between different SSDs is difficult to tell without benchmarking; from day to day use, you'd be hard pressed to tell the difference between most SSDs (although it may become more pronounced as significantly faster drives get released).

So it really comes down to personal needs and wants. Yes, there will be faster and faster M.2 based drives coming, and the 2 PCIe 2.0 lanes on that motherboard will hold some of them back, but the question is: will the performance difference matter to you? Do you need that higher performance? If yes, then look into a motherboard with an Ultra M.2 slot, like the ASRock Z97 Extreme6.

As for it working as a boot drive, well, I'll direct you to the section on the bottom of this page: http://www.anandtech.com/show/8045/asrock-z97-extreme6-...
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September 25, 2014 2:05:06 PM

all new asrock x99 provide 4x m.2 and bootable. the xp941 i get tomorrow as double speed on drive and who knows will soon be standard for all ssd. asrock is fast growing and nothing to do with asus nor cheap version. their x99 oc even has 2 4x m.2 ! i"ll order tomorrow.
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