# Asrock Z68 Extreme4 Gen3: PCI-E x16 slots not performing according to specs



## Starla (Dec 11, 2011)

Hi all.

I've recently built a new PC and I chose the Asrock Z68 Extreme4 Gen3. According to its official specs here:

- 2 x PCI Express 3.0 x16 slots (PCIE2/PCIE4: single at x16 or dual at x8/x8 mode) (PCI Express 3.0 with Intel® Ivy Bridge CPU, PCI Express 2.0 with Intel® Sandy Bridge CPU)
- 1 x PCI Express 2.0 x16 slot (PCIE5: x4 mode)

it features 2 PCI-E 2.0 (I'm using an i5-2500k) that perform at x16 when placing a single graphic card in either slot PCIE2 or PCIE4. When populating both slots (i.e. SLI config), both slots perform at x8. Finally the slot PCIE5 only performs at x4.

Well, the above is what I understand Asrock is offering according to specs, which I think are crystal clear.

Due to my CPU heat disipator size and planned arrangement I have to connect my graphic card (single, a GTX570) to PCIE4 slot, and expected it to perform at x16 as advertised. I picked this mobo considering this feature and disipator room requirements, among other parameters, of course.

To my surprise, PCIE4 is only performing at x8 according to GPU-Z (PCIE2 is empty). When I place my GTX570 in PCIE2 (by removing one of the CPU disipator fans), GPU-Z reports x16 performance (PCIE4 is empty).

The mobo User Manual (but not the advertised specs) says that "when using a single graphic card we _recommed_ to use PCIE2 slot for best performance". Not even here they are clearly stating that in order to get x16 performance you MUST use slot PCIE2, or that PCIE4 only performs at x8 (like i.e. they do for PCIE5 in the specs when stating it performs at x4)

1. Can anybody confirm whether on this mobo PCIE4 performs at x8 max, even when PCIE2 is empty? Can PCIE4 be set to perform at x16 in any way?

2. If answers to 1 are both negative, I plan to RMA the mobo for not performing according to specifications, hence my third question.

3. Can anybody list Z68 or P67 motherboard alternatives featuring at least 2 PCI-E 2.0 slot that can perform at x16, no matter the one I choose to connect a single graphic card? Please note: I do NOT mean SLI at x16, but single card at x16.

Thank you very much in advance.


----------



## Maban (Dec 14, 2011)

Only the first x16, PCIE2, is electrically x16. The second x16, PCIE4, will only ever provide up to x8 and the last x16, PCIE5, will only provide up to x4 (from the PCH). The only 1155 motherboards that are going to provide multiple x16 slots are ones with a PCIE switch, eg NF200 or Lucid Hydra (not the same as Lucid Virtu). FYI, that PLX switch on your board is splitting PCH lanes, not CPU. Currently the cheapest P67/Z68 motherboard on Newegg that features a NF200 switch is the ASUS P8P67 WS Revolution which is $226 after rebate. The performance difference between x16 and x8 is minimal, about 2% on average. So it's up to you to determine whether an extra 2% is worth the extra $50 difference between the Extreme4 and the NF200 boards. (It's not by the way.) Switches add a little latency themselves, though negligibly so, further making a single card solution with an NF200 impractical.

Here's some good info on how to identify lane configurations. Specifically my two longer posts.


----------



## Athlon2K15 (Dec 14, 2011)

+1 to maban


----------



## SonDa5 (Dec 14, 2011)

My MSI Z69 GD65 G3 operates the same way because only 1 PCI-E slot is built to support 16x.  Good thing about this is that when PCI 3.0 video cards are available both slots will be able to run at PCI 3.0 8X which is the same as todays PCI 2.0 16x.  Still limited but better than current PCI 2.0 slots.


----------



## Starla (Dec 16, 2011)

Thank you Maban.

I did some further research after my post and I completely agree with your recommendation. There are quite some articles showing that real life performance differences between playing at x8 or x16 PCI-E 2.0 are unnoticeable. Specially when my monitor max res is 1600x1200.

And yes, I came with the same reasonably priced mobo alternative, the WS Revolution, but given the above and the fact that I was going to perform at x16 over the NF200 chipset anyway (not native support) I decided to stay with the Asrock.

The good part is that I was overlooking an alternative case airflow arrangement which looks promising: CPU fans intake facing case front (not PCI-E slots, hence allowing me to use PCIE2) + top case fan as intake (not exhaust). This combined with side and bottom intakes (the only exhaust being rear fan right after CPU) can work very well. I plan to benchmark both fan configs.


----------

