NVIDIA GeForce GTX 1080 PCI-Express Scaling 38

NVIDIA GeForce GTX 1080 PCI-Express Scaling

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Introduction


The PCI-Express bus continues to be the most prominent system bus interconnect of this generation. It is so ubiquitous at moving ones and zeroes and yet so simple that other standards such as USB and Thunderbolt now use it at the physical level to let you plug in bandwidth-hungry external devices. Graphics cards continue to be the most bandwidth-intensive PCI-Express devices, and with increasing display resolutions and more in-game visual detail, PCI-Express bandwidth utilization of graphics cards is higher than ever. Both AMD and NVIDIA have launched new generations of GPUs primed for DirectX 12 and Vulkan. These APIs come with features such as virtual texturing (mega textures) that minimize GPU memory utilization at the expense of having to move data more frequently between the disk and memory.

We felt that it would be interesting to study how a contemporary high-end graphics card is utilizing the PCI-Express 3.0 x16 bus and how its performance is affected as we reduce the bus bandwidth by lowering the number of PCI-Express lanes available to it, and by falling back to older generations of PCI-Express, which affects the amount of data that can be pushed per PCI-Express lane. The last time we visited this question was exactly a year ago when we tested the AMD Radeon R9 Fury X in various PCI-Express modes. This year, we're testing the GeForce GTX 1080, the fastest graphics card that's readily available in all markets.



In this review, we are putting a GeForce GTX 1080 driven by the NVIDIA 375.70 WHQL software through our test bench, in full x16, x8, and x4 modes of PCI-Express gen 3.0, gen 2.0, and gen 1.1. This should tell you just how much the GPU is affected by bandwidth losses to fewer PCI-Express lanes and narrower older-generation PCI-Express lanes. The data should be particularly important to those weighing the impact of running two of these cards on a mainstream desktop platform (in which two PCI-Express x16 slots run at x8 bandwidth) as opposed to a high-end desktop platform, which provides full x16 bandwidth to the two cards, and that of PCI-Express gen 2.0 (older "Sandy Bridge" processors and the AMD FX platform).



We used adhesive tape to limit the number of PCI-Express lanes available to the graphics card, by physically blocking them off. The motherboard BIOS setup program lets us manually limit the PCI-Express bus to gen 2.0 and gen 1.1 bandwidths, from the gen 3.0 default.

Quite a few motherboards feature a third PCI-Express x16 slot that's electrical x4 and wired to the chipset instead of the CPU. We also tested the GTX 1080 on such a slot to check on the performance impact. This is particularly interesting because installing graphics cards into such slots could clog the DMI chipset bus.

Test System

Test System - VGA Rev. 45
Processor:Intel Core i7-6700K @ 4.5 GHz
(Skylake, 8192 KB Cache)
Motherboard:ASUS Maximus VIII Hero
Intel Z170
Memory:G.SKILL 16 GB Trident-Z DDR4
@ 3000 MHz 15-16-16-35
Storage:2x Patriot Ignite 960 GB SSD
Power Supply:Antec HCP-1200 1200W
Cooler:Cryorig R1 Universal 2x 140 mm fan
Software:Windows 10 64-bit Anniversary Edition
Drivers:NVIDIA: 375.70 WHQL
Display:Acer CB240HYKbmjdpr 24" 3840x2160
Benchmark scores in other reviews are only comparable when this exact same configuration is used.
  • All games and cards were tested with the drivers listed above, no performance results were recycled between test systems. Only this exact system with exactly the same configuration was used.
  • All games are set to their highest quality setting unless indicated otherwise.
  • AA and AF are applied via in-game settings, not via the driver's control panel.
Each game is tested at these screen resolutions:
  • 1920x1080: Most common monitor (22" - 26").
  • 2560x1440: Highest possible 16:9 resolution for commonly available displays (27"-32").
  • 3840x2160: 4K Ultra HD resolution, available on the latest high-end monitors.
We have color-coded the graphs so bars of the same color denote configuration with similar bandwidth on paper (eg: PCI-Express 2.0 x8 has similar bandwidth to PCI-Express 1.1 x16).

Anno 2205


After the smash-hit Anno 2070 from three years ago, Ubisoft is back with an even more futuristic sim set in the year 2205 in which mankind has colonized the moon beyond scientific expeditions, having established flourishing economies set way up there. In addition to that, you get to build inspirational cities set in various climates down here on Earth.

Based on a proprietary game engine, Anno 2205 takes advantage of DirectX 11, and unlike most RTS games, should be fairly taxing on modern graphics hardware owing to just how much more detail there is in the game's design and its models.

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