CrossfireX between PCI-E 2.0 x16 and PCI-E 2.0 x4

[Ahmadovich]

hey,guys

I have a R9 270 dual-x OC
and I'm gonna buy a new Mobo which is gonna support crossfiring 2 of that GPU in the future

I Firstly Choosed GA-970A-D3P
And browsed its specifications
http://www.gigabyte.com/products/product-page.aspx?pid=4642#sp

they say it supports CrossfireX
however they say it got
1 x PCI-E 2.0 x16 slot
1 x PCI-E 2.0 x16 slot (running at x4)

So is it okay for Crossfiring the 2 GPUs
and How much performance I will lose because of the x4 port
is it slight loss or huge loss

note : I Can't get better Mobo

 

[Venomous]

Crossfire knocks them both to 8x but sometimes you have to manually set the pcie speeds in bios. Hope that helps you out.

 

[Ahmadovich]

Crossfire knocks them both to 8x but sometimes you have to manually set the pcie speeds in bios. Hope that helps you out.

I can set a PCI-E x4 to be x8 ?! O,o

 

[Venomous]

I can set a PCI-E x4 to be x8 ?! O,o

From my experience with z68,77 and 87 boards, yes... You can set pcie lane speeds for slots. A lot of guys mine using 1x slots and risers too but obviously that's simply compute use.

I do prefer a motherboard that's at least labeled certified SLI compatible so you get at least 2 pcie lanes at 8x speeds. More of the expensive boards have 3-4 full speed 16x slots.

I'd suggest running a google search for that board just to make sure that 4x slot can be changed. I stopped using gigabyte boards in 2005 so I have no experience with their bios or options.

 

[Ahmadovich]

I do prefer a motherboard that's at least labeled certified SLI compatible so you get at least 2 pcie lanes at 8x speeds. More of the expensive boards have 3-4 full speed 16x slots.

it's CrossfireX Compatible
http://www.gigabyte.com/products/pro...px?pid=4642#sp

I'd suggest running a google search for that board just to make sure that 4x slot can be changed. I stopped using gigabyte boards in 2005 so I have no experience with their bios or options.

Couldn't find something about that :\

 

[BrightCandle]

I had a look at the manual for the motherboard and it says nothing about crossfire and nothing about the PCI-E slot reconfiguration. Infact in this case I am pretty certain its not possible because the 16x slot is attached to the northbridge whereas the 4x slot is coming from the southbridge. This just wouldn't allow reconfiguration. The slots on Intel Z87 come from the CPU but on this CPU they come from chips on the board and don't have the same features.

With that answered the question is how reasonable is PCI-E 2.0 16x and 4x for crossfire. Tomshardware did a test last year with higher performance cards than your own and determined there was some impact on performance with 4x but it wasn't usually problematic. It will certain reduce your scaling somewhat without a doubt, its just not enough bandwidth to not limit the cards.

 

[notty22]

I had a look at the manual for the motherboard and it says nothing about crossfire and nothing about the PCI-E slot reconfiguration. Infact in this case I am pretty certain its not possible because the 16x slot is attached to the northbridge whereas the 4x slot is coming from the southbridge. This just wouldn't allow reconfiguration. The slots on Intel Z87 come from the CPU but on this CPU they come from chips on the board and don't have the same features.

With that answered the question is how reasonable is PCI-E 2.0 16x and 4x for crossfire. Tomshardware did a test last year with higher performance cards than your own and determined there was some impact on performance with 4x but it wasn't usually problematic. It will certain reduce your scaling somewhat without a doubt, its just not enough bandwidth to not limit the cards.

Agree. Motherboard manufacturers choose to segment models this way. They could have (inexpensively) electrically wired those two pci-e slots to the north-bridge with a simple logic switch, but do not for their reasons.
Crossfire is often officially supported under 16x-4x, SLI, not so much.

 

[codyray10]

I run crossfire 7870's in 16x/4x config as thats all my motherboard supports. While I've never ran the setup on a 16x/16x motherboard, and cannot speak to the difference in performance between the two, I have no issues running 16x/4x. I can tell you though, there was still a pretty good performance boost when running benchmarks. I would say you may lose out on ~10% boost roughly

 

[Slomo4shO]

There shouldn't be much of an impact on performance running at 4X:

Comparison between generations:

 

[Ahmadovich]

I had a look at the manual for the motherboard and it says nothing about crossfire and nothing about the PCI-E slot reconfiguration. Infact in this case I am pretty certain its not possible because the 16x slot is attached to the northbridge whereas the 4x slot is coming from the southbridge. This just wouldn't allow reconfiguration. The slots on Intel Z87 come from the CPU but on this CPU they come from chips on the board and don't have the same features.

With that answered the question is how reasonable is PCI-E 2.0 16x and 4x for crossfire. Tomshardware did a test last year with higher performance cards than your own and determined there was some impact on performance with 4x but it wasn't usually problematic. It will certain reduce your scaling somewhat without a doubt, its just not enough bandwidth to not limit the cards.

thanks but written up there
"2-way CrossFire™ Support"
http://www.gigabyte.com/products/product-page.aspx?pid=4642#sp