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March 13th, 2018 13:00
Aurora R7 PCIe x16 slot actually only x8?
I just ordered my new R7. Was looking through the service manual. On page 19 & 20 the 2 PCIe x16 slots, items 16 and 20, are identified as PCIe x16 mechanical/x8 electrical. I was under the impression that the slot closest to the CPU always was PCIe x16 and used for a single GPU to run at the highest available bandwidth and speed. I don't know why Dell made a motherboard with this slot x8. Perhaps to save a few pennies on the bus interface components. Does reducing the bus width also reduce the overall speed that the GPU can operate at? I hope that by cutting the bus width in half the GPU speed is not cut in half also. Perhaps it is reduced 10% or 20%? Does anyone have information on the difference in x16 vs x8 operation? Should I cancel my order and look for a different computer with a fully functional x16 slot on the motherboard that can run the GPU at full speed? Would this limitation by Dell also reduce the speed of any other PCIe card when added in the other PCIe x4 slots?
Thanks,
Paul
Tesla1856
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March 13th, 2018 21:00
Yeah, it's been like that since the Aurora-R5 was released. Some of us back then had to come-to-grips with it (we originally thought something was broken). On the Aurora-R6 and higher it's marked on the motherboard slots and manual properly (I submitted those changes to Dell/Alienware and they listened ... along with some other things).
Main thing to remember is that it's PCIe-x8 (v3.0) which is the same bandwidth as a PCIe-x16 (v2.0) slot.
https://www.dell.com/community/Alienware-General/Alienware-Aurora-R5-NVMe-M-2-SSD-GTX1080-issues/td-p/5498977/page/4
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https://www.dell.com/community/Alienware-General/Alienware-Aurora-R5-NVMe-M-2-SSD-GTX1080-issues/td-p/5498977/page/7
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https://www.dell.com/community/Alienware-General/Alienware-Aurora-R6-Issues-with-GTX-1080-PCIe-3-0-lanes/m-p/5608846#M110435
Similar XPS and HP's are the same. You will have to move to a Area51-R3/R4/R5/R6 or custom build to get a PCIe-x16 (v3.0) slot ... but like those pages and links show ... I see no bottle-necks on my Aurora-R6 with GTX-1070.
pmg435T
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March 13th, 2018 22:00
Tesla1856:
Sorry I didn't catch those previous threads. I tried to search this subject on the board before posting but perhaps I didn't use the correct search parameters.
Obviously this x8 operation doesn't slow down the GPU, so everything should work fine. Just wish that this x16 (v2.0) and x8 (v3.0) bandwidth was made clear somewhere so there wouldn't be any confusion. I didn't know about the v2.0 and v3.0 differences.
Thanks for your information and helping allay my concerns.
Paul