As part of our review, ASRock sent us the 512 GB Samsung XP941 M.2 drive to test how ASRock has implemented the feature. For more information on the drive, check out Kristian’s review here. Kristian, due to his Z87 setup, had to use an M.2 x4 to PCIe adapter card, whereas with the Z97 Extreme6 we can test it direct.

On the Z97 motherboards we have seen so far, they have all implemented an M.2 x2 slot, with the two lanes coming from the eight PCIe 2.0 lanes possible off of the Z97 chipset. These slots are often also SATA capable, and share bandwidth with other SATA ports, a PCIe 2.0 x4 slot or the SATA Express implementation. The Z97 Extreme6 does this with its own M.2 x2 slot, but it has the Ultra M.2 x4 slot that comes direct from the CPU.

The Haswell CPUs for the Z97 platform have 16 lanes of PCIe 3.0 which are split into two lots of eight. One of these eight can be split into two lots of four, and it is typical to see on a motherboard a multi-GPU arrangement of x8/x4/x4 from the CPU. It is these last four lanes that ASRock has adapted for its M.2 slot, which means that when an M.2 drive is placed into the x4 slot, it will reduce the bandwidth of the first two PCIe slots down to x8/x4. This also disables SLI, due to NVIDIA’s requirement for x8 PCIe lane allocation (either PCIe 2.0 or 3.0) for each graphics card.

We tested the XP941 in both the x4 and x2 slots to find the general performance values of the drive when restricted by the x2 or given full reign of the x4. Because the x4 is rated at PCIe 3.0, ASRock is claiming a peak bandwidth of 32 Gbps, or 4 GBps, for drives attached. This would be a significant increase over the standard state of SATA storage, which tops out at 600MBps in real world implementations over a 6 Gbps connection. That would also imply that the 32 Gbps from the x4 should give 3.2 GBps as an upper limit.

We ran a series of tests with the XP941 in the M.2 x4, both while the integrated graphics was enabled and a discrete GPU (dGPU) in the first PCIe slot, and the M.2.

ASRock Z97 Extreme6 M.2 Performance
  M.2 x4 M.2 x4 w/dGPU M.2 x2
  Read Write Read Write Read Write
AS SSD 1095 918 1095 942 765 647
ATTO QD4 1015 1074 1028 1081 679 827
ATTO QD10 1013 1074 1020 1079 687 829
IOMeter 1347 1347 828
HDTach 1047 905 607

Using the drive in the M.2 x4 slot, with or without a discrete GPU in place, gives peak readings about the same, although with the discrete GPU in place ATTO shows some improvement in small transfer sizes (+30% at 4KB with QD10).

However the upshift from x2 to x4 shows the effect of a drive restricted against a drive that can stretch its legs. We move up from 765 MBps read to 1095 MBps read in AS SSD, a 43% speed up. We are still a way away from the 32 Gbps suggested by ASRock that this slot can handle, but it does mean the headroom is there for faster devices.

Moving on to the effect of losing lanes on discrete GPU gaming, we took the system with the M.2 equipped and tried our benchmarks on a single HD7970 (comparing x16 to x8) and two HD7970s in CrossFire (comparing x8/x8 to x8/x4).

Effect on Average FPS on PCIe 3.0 x16 to x8
  PCIe 3.0 x16 PCIe 3.0 x8 Difference
F1 2013 127.6 127.5 -0.1%
Bioshock Infinite 71.0 71.4 0.6%
Tomb Raider 44.6 44.4 -0.4%
Sleeping Dogs 48.3 48.1 -0.4%
Company of Heroes 2 42.9 42.3 -1.4%

On single GPU gaming, at our 1080p Maximum settings presets, gave almost zero difference with the bandwidth difference. The biggest drop was 1.4% for Company of Heroes 2. If this is the worst effect of dropping down from PCIe 3.0 x16 to x8, then I am encouraging all manufacturers, especially those making mini-ITX motherboards, to seriously consider ways to implement a M.2 x4 slot on their products.

This also has an effect on laptop computing, especially those with integrated discrete graphics cards. It means that the laptop manufacturer can implement either one or two M.2 x4 drives in a notebook and still have eight lanes for the GPU which will not be adversely affected in frame rates.

Now on to two-way CrossFire:

Effect on Average FPS on PCIe 3.0 x8/x8 to x8/x4
  PCIe 3.0 x16 PCIe 3.0 x8 Difference
F1 2013 117.5 113.6 -3.3%
Bioshock Infinite 133.3 131.8 -1.2%
Tomb Raider 87.2 88.0 0.9%
Sleeping Dogs 94.1 93.7 -0.4%
Company of Heroes 2 42.4 42.3 -0.3%

Here we see a bigger drop of 3.3% with F1 2013, and the bandwidth drop might affect us more if we had bigger screens at our disposal or a multi-monitor setup. But even 3.3% is not that bad, moving frame rates from 117.5 to 113.6 FPS is an arguable change at best.

All this points to one of several outcomes:

  • NVIDIA release their x8 lane restriction for PCIe 3.0 so users can implement SLI with M.2 x4
  • Intel increases the lanes on their mainstream CPUs to 20, giving x8/x8 allocation on PCIe and four lanes configurable M.2/SATAe
  • Nothing happens, because the performance on one GPU is not badly affected.

I will be hoping for a combination of the first two, just because it would open up more possibilities in this world of desktop computing.

OS Installation

A topic that has arisen on forums since the launch is whether the M.2 drives can be used as boot drives. For UEFI installation, the detection algorithm in the firmware has to be active to see the drive at the install prompt, however for Legacy installation the drive needs to implement its own firmware at POST. As the XP941 does not have initialization drivers, my Legacy Windows 7 install that I normally do for reviews, while it saw the drive at the OS installation screen, it was unable to hook the drive in to install. This is for both the M.2 x2 and M.2 x4 slots on the ASRock motherboard. Placing the drive into an ASUS motherboard showed no drive at all for Legacy installation, however Kristian has been in contact and confirmed that they are working on enabling UEFI installation for M.2 in a future BIOS update, as should all the manufacturers be if they have not already.

When the motherboard manufacturers have updated UEFIs, the following table should be relevant:

  Legacy OS Intall UEFI OS Install
M.2 without M.2 POST Firmware
(e.g. Samsung XP941)
No Yes
M.2 with M.2 POST Firmware
(e.g. Plextor M6e)
Yes Yes


Gaming Benchmarks: Sleeping Dogs, Company of Heroes 2 and Battlefield 4 ASRock Z97 Extreme6 Conclusion


View All Comments

  • 457R4LDR34DKN07 - Saturday, May 24, 2014 - link

    The Gen2 M.2 x4 PCIe looks very impressive. Its too bad that Asrock did not include this in their mITX offering. Reply
  • 457R4LDR34DKN07 - Saturday, May 24, 2014 - link

    I mean Gen3 Reply
  • smoohta - Saturday, May 24, 2014 - link

    Regarding the Dolphin benchmark- you wrote:
    "Results are given in minutes, where the Wii itself scores 17.53; meaning that anything above this is faster than an actual Wii for processing Wii code, albeit emulated."

    This should read "... meaning that anything below this is faster than..." - right?
  • Ian Cutress - Saturday, May 24, 2014 - link

    Bad choice of words - anything 'above on the graph' would be faster based on the orientation of results. I've updated it to remove the ambiguity. Thanks for pointing it out :)
  • r3loaded - Saturday, May 24, 2014 - link

    The overarching conclusion from this review - Intel needs to put far more PCIe 3..0 lanes on their CPUs and chipsets if we want motherboards where connectors don't play musical chairs with each other for bandwidth. Also, Samsung needs to make the XP941 a retail product right now! Reply
  • Tunnah - Saturday, May 24, 2014 - link

    I think the reasoning behind an either/or situation with M.2/SATAe is sound - the consumer most likely will not require 2 high end SSDs, and will go with one that is either M.2 or SATAe, the rest can be served via normal SATA ports.

    Also I think SATAe, while a great idea, will lose out to the convenience and capability of M.2; SATAe would have been great 2 years ago but now M.2 is here it is absolutely perfect for an OS drive, cutting down on not just size but cabling.
  • SirKnobsworth - Sunday, May 25, 2014 - link

    Agreed about SATAe, especially since (a) SSDs don't really need that much circuit board area and (b) A RAID array of two SATA SSDs offers at least as much theoretical bandwidth as a SATAe while taking up the same amount of ports on your board. Reply
  • Babar Javied - Sunday, May 25, 2014 - link

    Exactly my thought. So why have SATAe???? Its great that it uses PCI but it doesn't really offer anything that we couldn't already do.

    As you've said, "A RAID array of two SATA SSDs offers at least as much theoretical bandwidth as a SATAe while taking up the same amount of ports on your board".

    There seems to be a lot of stupid decisions being made regarding ports. DDR4 is another example of a useless upgrade.
  • Death666Angel - Tuesday, May 27, 2014 - link

    "A RAID array of two SATA SSDs offers at least as much theoretical bandwidth" But your are losing random performance when going RAID and increase the chance of a disk failure. Why would you even compare them? Reply
  • Galatian - Saturday, May 24, 2014 - link


    Can you explain to me why no mainboard manufacturer is using 4 lanes from the chipsets PCIe 2.0? I mean that would be enough for the Samsung SSD and still has room left. I mean what do I gain from all those SATA and USB ports? Who is actually using all of them?

    Right now I have to choose between either a slow M.2 slot because they only allocate 2 lanes or I can go with ASRock which feels like overkill and takes away CPU PCIe lanes.

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