3 of 3 people found this helpful
Both cards need to be installed in a PCIe 16 x8 speed slots for Crossfire to work. Plus your riser is PCIe 16 x1 not x8 or above. That riser is made to fit in a PCIex16 slot.
FROM AMD CROSSFIRE FAQ: https://support.amd.com/en-us/search/faq/233
How do I setup AMD CrossFire™ on my system?
If you would like to setup AMD CrossFire between two or more discrete graphics cards (PCIe socket cards) correctly, please read the following steps:
1. Please make sure that the power supply unit meets the recommended requirements of the complete AMD CrossFire setup. There are free 3rd party tools available online that can determine the power requirements of your system.
2. Check with your motherboard manufacturer that your motherboard is AMD CrossFire compatible with the required number of PCIe x16 slots available (running at a minimum of PCIe x8 speed).
3. Check the AMD CrossFire Compatibility Charts to verify that the cards you are using are recommended for AMD CrossFire.
4. Please make sure that you are properly grounded and the system is powered off before installing the graphics cards.
5. Connect the preferred card into the primary PCIe slot on the motherboard (check motherboard manual to determine the primary PCIe slot).
6. Connect additional cards to the secondary PCIe slots on the motherboard. Note: AMD CrossFire only supports up to 4 GPUs.
7. If any AMD CrossFire bridge cables were included with the graphics cards, please connect them now.
8. After starting up the system ensure that you install the latest compatible driver for the graphics cards.
9. Go to the AMD CrossFire option in the AMD Catalyst™ Control Center and make sure that the check box for "Enable AMD CrossFire" is checked.
Note: For AMD Dual Graphics setup with an APU and a single discrete graphics card connected to the PCIe slot please see the AMD Dual Graphics FAQ.
THANKS! So this means MSI is lying when claiming the P35 NEO2-FR as crossfire compatible?
On the q57 motherboard I have 2 slots: x4 and x16. However, they're PCI Express 2.0, while the P35 has 1.1...
1 of 1 people found this helpful
The P35 is a very old Motherboard (DDR2). It is possible that at that time Crossfire may have worked in PCIe16 x4. But now it seems you need a minimum of PCIe16 x8 speed for Crossfire and your motherboard specs definitely says it ONLY has two PCIe16 slots - x16 & x4 at version 1.1.
This old thread from Tom's Hardware explains a little better:
Ok, the PCIe xXX is the amount of lanes the slot has. so x16 has 16 lanes, x8 has 8 lanes and so on.
The physical slot on x4, x8, and x16 are all the same.
If it says 2 PCIe x16 slots it means that there are 2 slots on the board that are capable of 16 lanes.
If it says 2 PCIe X16 (and then in brackets says x16, x4 or x8, x8) it means when you have 1 slot being used it uses all 16 lanes for that 1 slot. But if you plug multiple things into the PCIe slots (most common 2 GPU's) it will divide the lanes between the cards. So that (x16, x4) you will have the first GPU running with 16 lanes, and the second GPU running with 4 lanes.
The manual for any board is going to say what the slot is at natively (x16, x8, x4) and how it reacts if in SLI (multiple GPU's)
For GPU's most of the time you are not going to notice a difference between 16x and 8x because GPU's can not fully saturate the bandwidth of the slot, therefore it is hardware limited, not bus limited.
2 GPU's in xfire / SLI on 2 8x slots will not fully saturate the bus.
Thanks for the explanations. The board that I compare it with has also a x16/x4 pair of slots, but PCI-Ex 2.0. On that one, Xfire works.
If I do the maths correctly, this means that, if they are double the bandwith of PCIEx 1.1, the x4 2.0 slot equals a x8 1.1, therefore I get Xfire on it and not on the P35.
The board must have PCIe x 16 - 3.0 x4 and x16. Otherwise Crossfire probably wouldn't work. PCIe 3.0x4 is the same as PCIe 2.0 x8.
according to this comment at a another Forum:
You can have a max of 20 lanes(i think, might be wrong) on a motherboard, unless you have a PLX chip.
PCI E 3.0 @ x8 is like a PCI E 2.0 running at x16
So, a motherboard with PCI E 3.0 can run two cards at x8 (so it's using 16 of 20 lanes), but they will operate at PCI E 2.0 x16 speeds.
A motherboard with two PCI E 2.0 lanes without a PLX chip will only run at x8 each (using 16 of 20 lanes), but obviously 2.0 is half the speed, so they will operate at 3.0 x4 speeds.
Any board running at more than x20 lanes total will be using a PLX chip, like the V Formula, which runs PCI E 2.0 @ x16x8x8 (x32 lanes) which is the equivalent of PCI E 3.0 running at x8x4x4 (a total of x16 lanes without needing a PLX chip)
PCI E 3.0 has double the bandwidth, meaning half the lanes will run at the same as the previous gen speed, but the same amount of lanes will allow a much higher datarate.
Thanks, that would conclude it.
As a side experiment, I ran these cards sepparately and individually connected to the motherboard via a PCIEx x16-x1 riser (so bottlenecked to x1). There was zero performance loss in games, meaning the GPU is too weak to saturate the bandwidth. I wonder why would AMD be so pretentious with this x8 requirement for XFire instead of just letting us be. Come on, AMD, free our cards.