PCI-e vs. M.2 SSD latency?

Discussion in 'SSDs & Data Storage' started by ponky, Aug 11, 2015.

  1. ponky

    ponky Limp Gawd

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    I'm still a bit lost with M.2 "tech". Could someone explain me a few things about M.2:

    - PCI-e mode vs. SATA mode, what's the difference? SATA mode uses SATA lanes, does it have worse bandwidth and/or latency than PCI-e mode?
    - Comparing M.2 NVMe SSD to "pure" PCI-e NVMe SSD, which one has lower latency? My guess would be PCI-e.

    Thanks in advance!
     
  2. drescherjm

    drescherjm [H]ardForum Junkie

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    SATA has both worse bandwith and higher latency. Although you will probably only notice the difference in benchmarks.
     
  3. Quix

    Quix 2[H]4U

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    M.2 NVMe vs PCI-E should be the same, provided both have the same number of lanes. The physical connector is the only difference, electrically it's the same.

    As for SATA vs PCI-E see the previous post.
     
  4. SomeGuy133

    SomeGuy133 2[H]4U

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    i think he was also asking about some M.2 take ACHI SATA or something. Like whats the difference and how do you tell. I think that is also what he was looking for.

    I know I have seen SATA M.2 and that honestly doesn't make sense because does that mean it doesn't work in M.2 that has PCIe lanes?
     
  5. Aesma

    Aesma [H]ard|Gawd

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    M.2 is a form factor, that's where the problem lies. M.2 SATA is no faster than normal SATA, its only use is if that's what your laptop offers.
     
  6. SomeGuy133

    SomeGuy133 2[H]4U

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    not trying to speak for him but i think thats what he is trying to understnad. So I am even curious.


    Does that mean you need a SATA m.2 for a SATA m.2 and a PCIe m.2 for a PCI2 m.2? I can't put a Samgsung SM951 NVMe into a m.2 SATA port/slot?
     
  7. ponky

    ponky Limp Gawd

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    I think some boards support both modes, so you could swap from bios. In SATA mode all data would go through SATA controller and one of the normal SATA ports would be disabled when m.2 is used, correct me if I'm wrong.
     
  8. Impulse

    Impulse [H]ardForum Junkie

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    It ultimately depends on the motherboard, the manual for the ASUS Z170-A I just bought states the M.2 port can be set to SATA OR PCI-E, so you could use either as long as it's configured properly.

    AHCI/NVMe is just the protocol used, most newer motherboards support either too but stuff like Z87 or older might not... For more info on that you should just read the two Anandtech reviews of the SM951 (they reviewed the AHCI version first and later the still non existent NVMe version).

    There's even U.2 adapters for M.2 slots that let you plug in cabled 2.5" PCI-E drives into them, how's that for confusing? :p And PCI-E riser/M.2 cards if you just wanna use an M.2 drive in actual PCI-E slot...

    I was kinda surprised how small M.2 are, I guess unconsciously I pictured them the size of a DIMM but they're barely the size of a SO-DIMM. I'm a little worried about heat and my newly purchased SM951, can't test jack until the 6700Ks go on sale tho.
     
  9. Impulse

    Impulse [H]ardForum Junkie

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    Sniped! But yeah... The SATA Express ports on my Z170-A get disabled when the M.2 is used in PCI-E mode.