ASUS PCIe 3.0 Dual x16 support - conflicting information about the P8Z77 WS

[phytoplankton]

I'm building a new PC with a single GTX Titan. To ensure future upgrading I was looking for a motherboard that supported PCIe dual x16. I must admit I have no clue if a GTX Titan SLI on x16/x16 performs noticeable better than a on x8/x8 but given the 6 GB ram I'd rather be safe than sorry.

I was about to order the ASUS P8Z77 WS based on its specification on their website.

https://www.asus.com/Motherboards/P8Z77_WS/#specifications

But according to its manual page 2-7. It only supports SLI in x8/x8

http://dlcdnet.asus.com/pub/ASUS/mb/LGA1155/P8Z77-WS/Manual&QVL/e7150_p8z77_ws.pdf

So is this a typo either in the specs or in the manual or am I simply not understanding something about how graphic cards work in PCIe 3.0 SLI?

 

[chesteracorgi]

The only LGA 1155 board the I have been able to spec out with dual 16 x 16 PCI lanes is : http://www.asrock.com/mb/Intel/Z77%20WS/index.us.asp?cat=Specifications. There are several choices for dual 16 X laned motherboards in LGA 2011, but that is a different platform, with more PCIe lanes. The only reason that the ASRock Z77 WS can use dusl 16 X lanes is because of the PLX PEX 8747 bridge. Normally the LGA 1155 chipset is limited to 24 (or 23) PCIe lanes and you need a bridge chip to get more. Look at this discussion for further info: http://www.overclock.net/t/1267524/how-many-16x-pcie-slots-the-ivy-bridge-i7-3770k-support.

Also, as I understand it the PCIe lanes are limited to the 2.0 rather than the 3.0 spec. So you will have to await new designs for a LGA 1155 to use dual PCIe 16 X at the PCI 3.0 spec. As the IB platform is coming to eol status you may need to go to a Haswell CPU for dual PCIe 16 X on the 3.0 standard.

 

[phytoplankton]

The only LGA 1155 board the I have been able to spec out with dual 16 x 16 PCI lanes is : http://www.asrock.com/mb/Intel/Z77%20WS/index.us.asp?cat=Specifications. There are several choices for dual 16 X laned motherboards in LGA 2011, but that is a different platform, with more PCIe lanes. The only reason that the ASRock Z77 WS can use dusl 16 X lanes is because of the PLX PEX 8747 bridge. Normally the LGA 1155 chipset is limited to 24 (or 23) PCIe lanes and you need a bridge chip to get more. Look at this discussion for further info: http://www.overclock.net/t/1267524/how-many-16x-pcie-slots-the-ivy-bridge-i7-3770k-support.

Also, as I understand it the PCIe lanes are limited to the 2.0 rather than the 3.0 spec. So you will have to await new designs for a LGA 1155 to use dual PCIe 16 X at the PCI 3.0 spec. As the IB platform is coming to eol status you may need to go to a Haswell CPU for dual PCIe 16 X on the 3.0 standard.

Yeah, I went to the ASUS support forum (which is damn near impossible to find btw) and they confirmed that it didn't truly support x16/x16 in PCIe 3.0. I just wanted the option of GTX Titans in dual 16x/x16 if possible in the future but I'm not willing to go LGA 2011 to get there. Thanks for your input

 

[pro_zlow]

I had a lot of problems trying to get my two GTX 1070 to benchmark well in SLI, but ultimately they were caused by power saving on the CPU. I can confirm that the Asus P8Z77 WS will support two Asus ROG STRIX OC GTX1070 cards in SLI (HW bridge). GPU-Z reports both at PCI Express Gen3 x16. 3DMark places my setup in the top 10% of similar rigs (Intel 3770K LGA1155), so I can confirm that my initial suspicions that the motherboard was too old to run the GPUs properly were ill-founded.

https://www.3dmark.com/3dm/22653587

I'm using BIOS 3505 (P8Z77-WS-ASUS-3505.zip) downloaded from the Asus support page:

https://www.asus.com/us/Commercial-Servers-Workstations/P8Z77_WS/HelpDesk_Download/

The manual (Section 2.2.4) says that two PCI Express graphics cards run only at x8:

http://dlcdnet.asus.com/pub/ASUS/mb/LGA1155/P8Z77-WS/Manual&QVL/e7150_p8z77_ws.pdf?_ga=2.137897017.848401627.1507807402-610489821.1506871241

but that's not been my experience using the latest BIOS. If you're getting poor game/benchmark performance, please check that the Asus (desktop) AI EPU tool is set on "high performance" and not "max power saving" because the latter has "chipset downgrade voltage" on by default.