Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I have ASUS P5Q3 Deluxe mobo, having 1 GeForce 9800 on PCIe 16x, 1 Xi-Fi Audio on PICe 1x.

Would like to install PCIe 1x USB 3.0 card in mobo PCIe 1x slot, but unfortunately the other 1x slot is blocked by video card. So the only option is to install it into 16x slot. Reading some forums I had an impression that this may slow down my system, in particular video card. If anyone can shed some light on this and to answer whether this will slow down the system(and what exactly, so I can measure before/after), I would appreciate it.

Mobo link

share|improve this question
I don't think the mobo you mentioned exist. Could you check the model number? – Feb 6 '12 at 10:28
sorry typo, updated – Pablo Feb 6 '12 at 13:27
up vote 1 down vote accepted

(From the comments:)

You may need to read the manual and find out which of the 3 PCIe x16 slots is the 4x one and plug your USB 3.0 card in there.

share|improve this answer

The "x"-Number is the number of lanes in a PCIe transmission.

It will not affect your system performance. The 16x slot will behave as such as it was a 1x slot.

With many boards the second 16x slot will tune down to 8x if a 16x card is put into the first 16x slot. This is not the case here, only 1 lane is used after all!

share|improve this answer
I think your reasoning is incorrect. The reason some motherboards need to slow down if two PCI-e x16 lots are populated is because they only have 16 PCI-e lanes for both slots. So if both are populated, the best it can do is x8 to each one. In his case, if it left the video card at x16, there would be no lanes left for the added card. – David Schwartz Feb 6 '12 at 9:45
Some motherboards still can run one at x16 and the other at x8 or AT LEAST at x4. It depends... But as said, the mobo does not exist, so either of our reasonings could be incorrect... – sinni800 Feb 6 '12 at 11:11
I agree. It could go either way. – David Schwartz Feb 6 '12 at 11:12
Sorry guys, it was typo. Now updated. Really need some conclusion whether to use that USB3 card or not and what will be the price. – Pablo Feb 6 '12 at 13:29
The specs of your mobo says there is "1 x PCI Express x16 slot at max. x4 link(black)" which is different from the other two PCIe x16 which share the 16x lane. You may need to read the manual and find out which of the 3 PCIe x16 slots is the 4x one and plug your USB 3.0 card in there. I suspect it's the black one at the very end of the card. The latest version of GPU-Z can give you the actual speed your card is running at (instead of the slot type). – Feb 6 '12 at 22:24

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.