Graphics card poor performance when in PCI-E 2.0 slot???

[kieranvyas]

I just finished building my workstation and was very disappointed to get very low scores in RealBench and Unigine Valley. My graphics card was initially in the PCI-E 2.0 slot on my X99 Pro mobo, but then I switched it to a PCI-E 3.0 slot and got literally double the scores. Is this difference normal between PCI-E 2.0 vs 3.0? I'm wondering if maybe something is faulty.

Unigine Valley Score using PCI-E 2.0: 1294
Unigine Valley Score using PCI-E 3.0: 2456

My realbench score using PCI-E 2.0:

Image Editing: 79808
Time: 107.507

Encoding: 111448
Time: 107.565

OpenCL: 60660
KSamples/sec: 1462

Heavy Multitasking: 64760
Time: 151.019

System Score: 67037

After switching to 3.0 my Heavy Multitasking time dropped to 93seconds!!

PCPartPicker part list: http://uk.pcpartpicker.com/p/jhCnrH

CPU: Intel Core i7-5820K 3.3GHz 6-Core Processor
CPU Cooler: Noctua NH-D15 82.5 CFM CPU Cooler
Motherboard: Asus X99-PRO ATX LGA2011-3 Motherboard
Memory: Crucial 32GB (4 x 8GB) DDR4-2133 Memory
Storage: Samsung 850 EVO-Series 250GB 2.5" Solid State Drive
Storage: Western Digital BLACK SERIES 1TB 3.5" 7200RPM Internal Hard Drive
Storage: Western Digital BLACK SERIES 2TB 3.5" 7200RPM Internal Hard Drive
Video Card: EVGA GeForce GTX 970 4GB SSC ACX 2.0 Video Card
Case: Fractal Design Define R5 (Black) ATX Mid Tower Case
Power Supply: XFX XTR 750W 80+ Gold Certified Fully-Modular ATX Power Supply
Operating System: Microsoft Windows 8.1 (OEM) (64-bit)
Case Fan: Noctua NF-A14 PWM 82.5 CFM 140mm Fan
Monitor: Dell U2515H 60Hz 25.0" Monitor

[usually_quiet]

Check the manual. That will tell you the limitations on the expansion slots. For example if they share bandwidth with other expansion slots and other connections on the board, or use fewer lanes.

The manual for the X99 Pro says the following:

1 x PCI Express 2.0 x16 slot*** (max. at x4 mode, compatible with PCIe x1 and PCIe x4 devices)

That means it functions as if it were an x4 slot rather than an x16 slot when a video card is installed.

[Edit]There is usually one video card slot that is supposed to be populated first. Additional x16 slots are usually intended to be used for SLI or crossfire.

[kieranvyas]

Check the manual. That will tell you the limitations on the expansion slots. For example if they share bandwidth with other expansion slots and other connections on the board, or use fewer lanes.

The manual for the X99 Pro says the following:

1 x PCI Express 2.0 x16 slot*** (max. at x4 mode, compatible with PCIe x1 and PCIe x4 devices)

That means it functions as if it were an x4 slot rather than an x16 slot when a video card is installed.

[Edit]There is usually one video card slot that is supposed to be populated first. Additional x16 slots are usually intended to be used for SLI or crossfire.

Thanks for that information! I'm really new to this so learning all the time. If you could answer one more question... The manual says;

The PCIe x16_3 slot supports x8 devices only

What does this mean? Is there any reason my EVGA GTX 970 SSC shouldn't be in this slot?

[usually_quiet]

The PCIe x16_3 slot supports x8 devices only

What does this mean? Is there any reason my EVGA GTX 970 SSC shouldn't be in this slot?

In my post above, I wrote "There is usually one video card slot that is supposed to be populated first." Chapter one page 14 (1-14) in the PDF version of the manual provides ASUS's recommendations for installing VGA cards. According to those, you shouldn't be using the PCIe x16_3 slot unless you have two video cards installed. If you have only one video card installed, it should be in the PCIe x16_1 slot

As you saw, the PCIe x16_3 operates as a x8 slot rather than an x16 slot. While x8 might not significantly decrease the performance of some less powerful video cards, I would think that you would want a GTX 970 in the slot that provides the best possible performance.

[newpball]

It definitely should be in the first slot as recommended by the manual.

[kieranvyas]

Thank you very much!!