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M.2 SSD PCIe 3.0×4 vs 2.0×4 | Tom’s Hardware Forum

Posted by jpluimers on 2021/10/27

I wanted to know the influence of PCIe versions to NVMe support, and found [Archive.is] M.2 SSD PCIE 3.0×4 vs 2.0×4 | Tom’s Hardware Forum answering:

You already know that the Z97 motherboard has one M.2 port. The problem is there are several M.2 variations. Here are the current possibilities:

M.2 3.0 x4 – State of the art M.2 SSD that uses 4 PCIe 3.0 channels for proper operation. The M.2 port on the motherboard is sometimes referred to as an Ultra M.2 port. It is the appropriate port for the Samsung 950 Pro SSD.

There are other M.2 SSDs that either use PCIe 2.0 or use fewer PCIe channels:

  • M.2 2.0 x4
  • M.2 2.0 x2
  • M.2 SATA 3

You will need to check your motherboard manual or the company web site to determine if the M.2 port can support an M.2 3.0 x4 SSD like the 950 Pro. A lot of the Z87 and Z97 motherboards had M.2 ports for M.2 2.0 x2 SSDs that would not fully support an M.2 3.0 x4 SSD. With the exception of ASRock, the other motherboard manufacturers did not do a very good job of fully identifying the M.2 ports. You will have to find a little more information about the M.2 port on your motherboard. Hopefully the information is in the owner’s manual or the manufacturer’s web site.

The addition of M.2 ports on the the motherboard required the use of additional PCIe channels. Unfortunately Intel resisted adding chipset support for additional PCIe channels until recently. The lack of a sufficient number of PCIe channels resulted in some awkward solutions:

  • Some motherboards reduced the number of channels available to graphic cards. The cards might be reduced from PCIe 3.0 x16 down to PCIe 3.0 x8. Graphic card performance is reduced by about 5%. That is not a terrible hit in performance.
  • Some motherboards reduce the number of SATA 3 ports that are available. For example,the MSI Z107 Titanium motherboard has two M.2 3.0 x4 ports. If I install a 950 Pro in each port, then all of the standard SATA ports are disabled except for two ports. The M.2 ports do not reduce the performance of graphic cards
  • Some high end motherboards add an expensive PLX chip to handle M.2 SSDs. An example would be the ASRock Z97 Extreme9 motherboard. The PLX provides direct data transmission between the M.2 SSDs and the cpu. It is actually possible to run two graphic cards in SLI at PCIe 3.0 x16 each and still be able to run two M.2 SSDs.

The Samsung 950 Pro uses the new NVMe protocol instead of AHCI. A motherboard would have to have a UEFI BIOS, an Intel chipset, and a Microsoft Windows operating system that support the NVMe protocol. You would have to do the following:

  • Check for any BIOS updates. Sometimes the updates include new and improved support for the NVMe protocol.
  • Check for any Intel chipset updates. Sometimes the updates include new and improved support for the NVMe protocol.
  • Windows 7, 8, and 10 can support the NVMe protocol. Again you will have to check for updates or fixes that can improve NVMe support. NVMe is new so things could get a little complicated.
  • Finally Samsung has issued their own NVMe driver for the 950 Pro. Reviews and articles indicate the Samsung NVMe driver is better than the Windows NVme drivers.

Some modern motherboards still provide a PCIe 2.0 slot. That does not mean you should purchase a PCIE 2.0 SSD or an M.2 SSD with an adapter card. M.2 3.0 x4 SSDs are backwards compatible.

It might be confusing but for all practical purposes it is just a matter of checking requirements and specifications.

Note I have bulleted some entries for readability and bolded some text relevant to some motherboards I still have running and fixed some typos.

On connectors and B/M keying:

  • M.2: Form factors and keying – Wikipedia (in the table, I bolded the B and M keys as they are used most often)

    M.2 module keying and provided interfaces[4]:8[12]:3[16][17][18]
    Key
    ID
    Notched
    pins
    Provided interfaces
    A 8–15 PCIe ×1, USB 2.0, I2C and DP ×4
    B 12–19 PCIe ×2, SATA, USB 2.0 and 3.0, audio, UIM, HSIC, SSIC, I2C and SMBus
    C 16–23 Reserved for future use
    D 20–27
    E 24–31 2× PCIe ×1, USB 2.0, I2C, SDIO, UART and PCM
    F 28–35 Future Memory Interface (FMI)
    G 39–46 Reserved for custom use (unused in the M.2 specification)
    H 43–50 Reserved for future use
    J 47–54
    K 51–58
    L 55–62
    M 59–66 PCIe ×4, SATA and SMBus

–jeroen

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