PCI Express And SLI Scaling: How Many Lanes Do You Need?

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Are the most elaborate platforms really required to host the fastest GPUs, or can you get away with P55's lane-splitting scheme? As Nvidia’s latest graphics processors push 3D performance to new heights, we examine the interfaces needed to support them.

Test Setup And Benchmarks

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Test System Configuration
CPUIntel Core i7-920 (2.66 GHz, 8 MB Shared L3 Cache), Overclocked to 4.00 GHz at 1.40 V, 200 MHz BCLK
MotherboardMSI Big Bang-XPower, BIOS V1.2 (06/09/2010), Intel X58 Express, LGA 1366
RAMKingston KHX16000D3ULT1K3/6GX (6 GB), DDR3-2000 at DDR3-1600 CAS 7-7-7-21
GTX 480 GraphicsMSI GeForce GTX 480 1.5 GB, 700 MHz GPU, GDDR5-3696
OS Hard DriveWestern Digital VelociRaptor WD3000HLFS, 300 GB, 10,000 RPM, SATA 3Gb/s, 16 MB cache
SoundIntegrated HD Audio
NetworkIntegrated Gigabit Networking
PowerOCZ-Z1000 1000 W Modular ATX12V v2.2, EPS12V, 80 PLUS Gold
Software
OSMicrosoft Windows 7 Ultimate 64-bit
GeForce GraphicsNvidia ForceWare 258.96
ChipsetIntel INF 9.1.1.1020

Our Core i7-920 is overclocked to 4.00 GHz in an attempt to remove the “CPU cap” on 3D performance.

Thermalright’s MUX-120 keeps our overclocked CPU cool enough to pass stability tests.

With a mid-load efficiency of around 91% and an 80 PLUS Gold rating, OCZ’s Z1000 power supply provides optimal “full system” power testing. Because its efficiency curve dips to around 89% at its ends, readers can multiply today’s input power readings by 0.90 to calculate output power within ±1%.

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Benchmark Configuration
3D Games
Aliens Vs. Predator BenchmarkAlien Vs Predator Benchmark Tool Test Set 1: Highest Settings, No AA Test Set 2: Highest Settings, 4x AA
Call of Duty: Modern Warfare 2Campaign, Act III, Second Sun (45 sec. FRAPS) Test Set 1: Highest Settings, No AA Test Set 2: Highest Settings, 4x AA
CrysisPatch 1.2.1, DirectX 10, 64-bit executable, benchmark tool Test Set 1: Highest Quality, No AA Test Set 2: Highest Quality, 4x AA
DiRT 2Run with -benchmark example_benchmark.xml Test Set 1: Highest Settings, No AA Test Set 2: Highest Settings, 4x AA
S.T.A.L.K.E.R.: Call Of PripyatCall Of Pripyat Benchmark version Test Set 1: Highest Settings, No AA Test Set 2: Highest Settings, 4x MSAA
Synthetic Benchmarks and Settings
3DMark VantageVersion: 1.0.1, GPU and CPU scores
TOPICS
Thomas Soderstrom
Thomas Soderstrom
Thomas Soderstrom is a Senior Staff Editor at Tom's Hardware US. He tests and reviews cases, cooling, memory and motherboards.
80 Comments Comment from the forums
  • Mousemonkey
    There are quite a few folk who have been waiting for this.
    Reply
  • zorky9
    This would even add more value to the i5-750 in your best CPU for the money article.
    Reply
  • amk09
    I love how people always bash on x8 x8 and how it sucks, when in reality x16 x16 is only 4% better.

    You spend unnecessary $$$ on a x58 platform while I save money that I can put towards a GPU upgrade with my p55 platform :)
    Reply
  • carlhenry
    i'm curious how other games are "dependent" on bandwidth while others are not... does that mean that the games that aren't dependent on bandwidth isn't using the full potential given the the size advantage of x16 over the x8? i wish every game would utilize every inch of your hardware in the future.
    Reply
  • sambadagio
    For all your fps hunters, I bet you only have a screen at home with 50 or 60Hz. So just for your information, everything above 50 or 60fps is just useless... In this aspect, a PCIx 4x is actually enough... ;-)

    Reply
  • luke904
    so a 4850 crossfire setup will hardly be bottlenecked by an 8 lane motherboard.

    anyone know if 4850's are going to be unavailable any time soon? You could get the 3000 series for quite awhile after the 4000's released so I'm crossing my fingers until i can afford a cpu upgrade and another 4850

    cpu is currently a 7750BE and so im pretty sure it would bottleneck the 4850's. I think it does with just one actually.
    Reply
  • jgv115
    @ carlhenry

    It's not the game's fault. The GPU can only go as fast as it was made to go. So in simple terms you could say that GPUs these days aren't "fast" enough to use all the bandwidth PCI Express offers.
    Reply
  • outlw6669
    Very nice review but I have to ask, why did you not test with 5970's?

    On a card for card basis they are still quite a bit more powerful than the GTX 480 and should require the most bandwidth of any current card for maximum performance.
    Reply
  • barmaley
    This review tells me that if you already have an i7 and at least 2xPCIe 16x lanes on your motherboard then in order to play modern games, all you are going to be upgrading for the next several years is your graphics.
    Reply
  • Aionism
    Even though I'm not interested in SLI I am glad to finally see a benchmark comparing PCI-E x16 and x4. My motherboard only allows me to use my video card in my x4 slot for some reason. I've been wondering how much performance I've been losing over that.
    Reply