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Thread: GA-P55A-UD4P - SATA/USB bandwidth?

  1. #1
    Join Date
    Dec 2009
    Cleveland, OH

    Default GA-P55A-UD4P - SATA/USB bandwidth?

    Just posted this in the general motherboards forum by mistake...

    Anyway, I just purchased a GA-P55A-UD4P board today. I have not yet even broken the seal on the static bag.

    I'm just trying to make some sense of this here. I read before buying it that using SLI/CF would disable SATA3 and USB3. That's fine, I don't care about dual video cards. But I noticed a block diagram in the manual showing that the Marvell SATA 3.0 controller and the NEC USB 3.0 controller were each connected via a PCIe x1 lane. A PCIe x1 lane is only capable of 250MB/s - this is technically less bandwidth than SATA 2.0. And we're trying to run two ports off of this? USB 3 has the same issue.

    What doesn't make sense here is, why would SLI/CF disable the high-speed interfaces? Are these interfaces in fact using some of the video card bandwidth too? I've been hearing all kinds of conflicting stories regarding this and I'd appreciate a clear answer.

    I bought this board to be future proof. If these ports are going to be limited by the PCIe bandwidth, I want to know about it before I break the seal on this motherboard.


  2. #2
    Join Date
    Dec 2009
    Cleveland, OH

    Default Re: GA-P55A-UD4P - SATA/USB bandwidth?

    Bump? Anyone?

    This is what the manual says:

    Turbo SATA3 / USB3.0 (Marvell 9128 /NEC USB 3.0 Controller)
    Determines whether to set the PCIe speed of the Marvell 9128 or NEC USB 3.0 controller to PCIe Gen 2. Please note that when only one graphics card is installed on the PCIEX16 slot, it will operate at up to x8 mode if either one of the two controllers is set to PCIe Gen 2. The two controllers will be automatically set to PCIe Gen 1 when two graphics cards are installed on the PCIEX16 and PCIEX8 slots.

    Auto Lets the BIOS automatically confgure this setting, depending on the device installed.
    Turbo SATA3 Sets the PCIe speed of the Marvell 9128 controller to PCIe Gen 2.
    Turbo USB3.0 Sets the PCIe speed of the NEC USB 3.0 controller to PCIe Gen 2.
    Disabled Disabled forces the Marvell 9128 and NEC USB 3.0 controllers to PCIe Gen 1.
    To be clear, I have heard that:

    1. Using SATA3 or USB3 disables the second x16 slot

    2. Using SATA3 or USB3 reduces the speed of the first slot to 8x

    3. Both 1 and 2

    4. SATA3 and USB3 use an x1 lane on the P55

    5. SATA3 and USB3 use some of the graphics bus on the CPU

    6. You can't use both SATA3 and USB3 at the same time

    I can't seem to find any clear answer here.

    What I gather from the manual is that if enabled the SATA/USB will use a PCIe 2.0 lane (500MB/s), otherwise it will use a 1.0 lane (250MB/s). Since according to the block diagram they are connected via a 1x lane. Both of these solutions would cause a bottleneck. So is this board capable of providing full bandwidth?

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