But, I've just found that my PCIE bus bandwidth is limited to 1.6GB/s, each way, where it should about 6 GB/s using x16 v2.0 slots. I've tried every card in every slot, one at a time, and always get the same numbers. I have also updated and reinstalled main board bios and drivers, Intel drivers, AMD drivers, and used every BIOS configuration that might help. PCIE data rate is measured using programs like PCIeBandwidth.exe and PCIspeedtest.exe from AMD. What I get is:
PCIe x4 slot, transfer rate=1.3 GB/s (read and write) (one card)
PCIe x16at x8, transfer rate=1.65 GB/s (read and write) (requires 2 cards)
PCIe x16 at x16, transfer rate=1.65 GB/s (read and write) (one card)
The x4 slot is always just a bit slower. System: ASRock z68-Extreme7 motherboard, 5 PCIE slots, one for PCIE v3.0, 3 for multi GPUs (x16, x16, 0) or (x16, x8, x8) and a dedicated x4 speed slot, with Windows7 x64. The main board also uses PLX PEX8608 and NL200 chips to increase the number of PCI lanes.
I would love to know if anyone has seen similar problems with PCIE performance, or if anyone can verify that the new AMD drivers (I'm using the 12.3 driver dated February 16 at AMD) are running at full speed (5 to 6 GB/s). I think it is rather strange that all the slots run the same speed. I don't think this would be a hardware design problem but it's really hard to know until the problem is solved.
BTW, I also checked using GPU-z which says the cards are configured as x16 v2.0 when in the x16 slots.
It's been a frustrating week searching for clues and any help is very much welcome.
Edited by relee - 3/2/12 at 4:27am