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Thread: X99 OC Formula m.2 slot and BCLK

  1. #1
    Join Date
    Dec 2014

    Default X99 OC Formula m.2 slot and BCLK


    I was just about to buy one of the smaller (256 GB) m.2 drives, the XP941, when I read this in my motherboard manual, "When you overclock the BCLK frequency, it is recommended that you install the M.2 PCI
    Express module to the M.2 Socket (M2_1)". Anyone know exactly what this means and why it would be like that? The M2_1 slot that it recommends using is the slower PCIe2 x 4 slot, not the new ultra slot. Does this mean that using a drive in the ultra slot is likely to inhibit BCLK changes? I was hoping to buy a smaller capacity PCIe2 drive like the XP941 and get a second (faster) m.2 drive that uses the full capacity of the ultra slot, like the SM951 when it is released. Does anyone know:

    1) Will I have problems using both m.2 slots?
    2) If I eventually use the ultra m.2 slot, will I not be able to overclock the BCLK?

    Thanks for any help!

  2. #2
    parsec's Avatar
    parsec is offline Senior Member
    Join Date
    Jun 2012
    Third stone from the sun

    Default Re: X99 OC Formula m.2 slot and BCLK

    The reason ASRock recommends that in the manual is simple, but brings up a couple questions.

    The Ultra M.2 slot uses PCIe 3.0 lanes provided by the CPU.

    The standard M.2 slot (M2_1) uses PCIe 2.0 lanes provided by the X99 chipset. You're lucky that the X99 chipset has more PCIe 2.0 lanes than the Mainstream boards, like a Z97, whose standard M.2 slot is only an x2 lane interface, rather than the x4 interface on your board.

    The manual's caution about using the Ultra M.2 slot when over clocking the BCLK is due to the BCLK being tied to the PCIe 3.0 clock in the CPU. An increase in the PCIe 3.0 clock may cause problems with an M.2 SSD's controller chip. The controller chip expects the PCIe clock to be within a certain range, and if that clock is outside of that range, it becomes unstable.

    The X99 chipset's PCIe clock is not tied to the CPU's BCLK, so is unaffected by BCLK changes.

    Intel actually experimented with SSD controller over clocking. It can be done, but the increase in performance was not that substantial, and the SSD controller was hotter than normal, just like over clocking a CPU does.

    X99 boards have BCLK "straps" of 125, 167, etc, but I thought those were supposed to be independent of other system clocks like the PCIe clock. Mainstream Intel boards can have the same type of BCLK straps, but it is not clear if they do or do not affect other system clocks. A Z87 board I use has BIOS options that seem to keep those clocks separate (or imply that they can), but I've never experimented with them enough.

    Actually, that warning might be a safety measure, given how some M.2 SSDs have been found to operate. That is, the XP941 runs hot, and if it is in effect "over clocked" with a higher BCLK/PCIe clock, it will run even hotter.

    What kind of BCLK over clocking are you referring to, a few MHz over the standard 100MHz, or via the straps of 125, 167, etc? BCLK OC's are more difficult to get working on Haswell processors, and Ivy and Sandy Bridge too.

  3. #3
    cowtung is offline Junior Member
    Join Date
    Dec 2014
    Berkeley, CA

    Default Re: X99 OC Formula m.2 slot and BCLK

    From everything I've read, you don't need to mess with BCLK unless you are trying to get memory speeds higher than around 2666 (can't remember exact number). What memory are you using? I don't think messing with BCLK will do much for you besides increase instability for very small percentage gains in benchmark tests. If you have to "underclock" your 3000 rated ram to 2666 in order to get the BCLK to 100 in order to use a PCIe3 x4 SSD, the tradeoff in RAM speed for SSD speed is probably worth it.

  4. #4
    Join Date
    Dec 2014

    Default Re: X99 OC Formula m.2 slot and BCLK

    Dear apmontgo

    Regarding about Samsung Ultra m.2 SM951 is a new release product.
    If want to use this SDD on X99 OC Formula, you can try below link of special BIOS L1.72, this BIOS add compability with SM951.
    Now we are still testing this BIOS, if this BIOS can pass our test, we will release it to our official website.


    ASRock TSD

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