Should I use PCIe 1x or 16x for dual-port USB3 card?

WinXP Pro, Asus Rampage Formula mobo with 3.8GHz QX9650, new Sharkoon USB 3.0 2-port card and dual HD dock. All the mobo PCIe slots are v2. There is a separate USB3 cable from each of the two ports on the new card to each of the HD slots in the dual dock i.e. they don't share a cable like some USB2 dual docks. I installed the 2-port USB3 card in a PCIe x1 slot. With it I am getting about 80MB/s copying between my PC and each HD in the dual dock. But when I copy between the HDs in the dock, it drops to 50MB/s.

I have a spare PCIe x16 slot. I'm wondering if I can expect the intra-dock HD-HD transfers to be faster if I install the 2-port USB3 card in that slot, because I guess each port can then have its own PCIe lane, whereas now they are sharing one.

Of course I could move the card there and try it, but I find this card to be *extremely* finicky about its seating. It took a long time to massage things to the point where it doesn't constantly disconnect, and I don't want to go through that again. Beware of this if you buy one. Also, keep the USB3 cables away from your display cable as that too may cause disconnects.

Any input appreciated, thanks. Sorry if this appears as a dupe but my prev post seems to have disappeared.
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  1. Is the controller PCI-express x1? Then it could be either 250MB/s or 500MB/s. Using well insulated cables (no break-out cables!) is highly recommended, yes.
  2. That's a good question. I tracked down the NEC datasheet at:

    and see that it is a single lane. So plugging it into a slot with more than one lane won't speed it up.

    Mine has started disconnecting again, even in the x1 slot where I thought it was stable. General warning on this. Reminds me of eSATA now.

    Thanks for the help.
  3. Further information for folks looking at these USB 3.0 PCIe adapters...

    1) If it only offers two USB ports, using the NEC µPD720200 controller, then it only needs a PCIe x1 slot. You can put it in a x4 or x16 slot but the additional PCIe lanes won't be used. Note that there are some combo cards that offer more than just the USB 3 ports; these will require a x4 or higher slot.

    2) This is not specific to USB 3.0 of course, but that's where I encountered it big time: These small PCIe x1 boards only have about 1/2" of total connector mating. So, unlike a graphics board in an x16 slot, there isn't a lot of gripping force. That means two things. First, the board mounting flange must be mounted *tightly* to the case metal with a screw - toolless plastic clips will probably not be sufficient. There can't be *any* lateral movement at the flange.

    Second, given variations in case / mobo alignment, it is possible that with the flange screwed down securely, the board won't be seated perfectly in the slot. It may be tilted axially e.g. the pins nearest the flange may be fully seated but the ones further away pulled out a little. So you may have to bend the flange a little to get a perfect final fit.

    However, with all this finally done right, my board works great. It's about 3x faster than USB 2 in real-world tests, and all my problems with getting USB 2 drives to connect and disconnect gracefully have disappeared.
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