Radeon HD 6990 Bandwidth Comparison Test 16x vs 8x vs 4x 3DMark 11 Linus Tech Tips
Linus Tech Tips
·Linus Tech Tips
·2011-05-08
·
826 words · ~4 min read
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So, as a follow-up to my recent video where I took two GTX 580s, threw them on
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the Gigabyte G1 Gorilla motherboard, and I tested in dual 16x mode in SLI and
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dual 8x bandwidth mode in SLI. I am
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going to be taking an even higher an even more demanding card, the Radeon
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HD6990, and I'm going to be running it in a single card configuration in a 16x
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slot, an 8X slot, and finally a 4X slot
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to find out what difference there is. In terms of performance, I'll be using the
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3D Mark 11 extreme preset. Now, please
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note that the extreme preset will not show as much of a difference as one of
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the lower quality presets, uh, such as
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the entry or performance presets. But what it does give us is a more realistic
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real world scenario because most people are not going to be using a 6990 to run
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Quake 3 at 1024 x 768. So, you're going
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to be turning up the details, you're going to be turning up the res. So, that is the scenario that we will be looking
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at. Something to bear in mind before I get too far into my testing here is that
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the top slot at 16 and the second slot at 8X are both running off the PCI
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Express controller integrated into the Sandy Bridge CPU on this board which is
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clocked at 4.7 GHz by the way to eliminate any CPU bottlenecking or as
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much as possible. The bottom slot actually runs off of the chipset at 4x
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speed. So, it has an additional disadvantage that is not shared by the
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top two slots. So, just bear that in mind. Take the results with a bit of a
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grain of salt, but I don't have another platform handy where I can show you 16x,
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8x, and 4x where they will all be equal.
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So, my 16x result is a score of
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3,330. So, I'll be back with 8x and 4x
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results shortly. Now, this may look like a stupid configuration. I've got my 6T90
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and a GTX 580 here. But the reason I've installed the GTX 580, which won't
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affect my benchmark scores in any way, is to force these PCIe lanes to go from
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16x to 8x8x. So, you can see here within
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GPUZ, the 6990 reports as running at
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16x. And while that may be true because
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it's running internal Crossfire where each GPU is getting 16x bandwidth from
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the uh from the lane spplitter that's on the PCB
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itself. The actual lane splitter itself is only
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getting if we look here at the GTX 580.
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So you can see that the actual bandwidth to the slot is only 8x because it is
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correctly split at this time. So my benchmark results are
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3,312 3D marks. So we have seen
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a difference in performance between 16x
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and 8x
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312. Okay, very small, very small. And I
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will be back with PCIe 4X results very
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shortly. So at the end of the day, this video becomes more about how if you
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internally bottleneck a card um
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according to the computational resources
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located on the card that the amount of PCI Express bandwidth you supply it with
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is actually going to make very little difference in terms of performance. Now,
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something to bear in mind too about this particular testing setup today. You can
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see I had to nudge my motherboard over a little bit to get the uh 6T90 to fit
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into that bottom slot on my tech station. But so, I've got it in the PCIe
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4x slot. Now, think about it this way.
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Basically, I've got two GPUs. I have on a 6990, I pretty much have two 6970
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GPUs. Okay? So, so bear with me here.
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So, by the comparison I did the other day where I was comparing
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16x6 and 8x8x SLI, this is basically running it
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on this motherboard, this card in 16X mode is pretty much like running two
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cards, two high-end single GPUs at
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8x8x, 4x4x in the 8x slot, and then at
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2x 2x in that 4x slot at at the very
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bottom that that's essentially the amount of bandwidth we have available
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per GPU and we still see very very
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little fluctuation in terms of the overall score. So, what I may have to do
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in the coming uh next little while is do
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an updated video about this where I find a slightly less uh GPU speed
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bottlenecked benchmark and uh demonstrate maybe more of a more of a
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typical or worst case scenario for how much the PCI Express bandwidth affects
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single card performance. So, thank you for checking out this little episode of
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