Introduction

At the time of writing, we've gotten our hands on three NVIDIA GeForce GTX 1080 graphics since its launch. We typically get a 2-way SLI review out fairly soon after the launch review, but two things pinched us - availability of our second card and the new SLI HB bridge. With the GeForce "Pascal" architecture, instead of driving its GPU lineup toward DirectX 12 native multi-GPU, which has some fascinating features on paper, such as the ability to mix and match any two GPUs that support the same API (D3D 12_0 and above), NVIDIA developed its proprietary SLI technology further and made it even more restrictive than before.

The GeForce GTX 1080 does not support 3-way and 4-way SLI. Not officially or, now, even unofficially. There's very limited support for a few non-gaming apps, including competitive benchmarks, but beyond that, 3-way and 4-way SLI is of no use to gamers. We feel this is unfair, especially when monitor resolutions, color depth, and such bandwidth-intensive features as hardware HDR are finally on the rise. It would have been great if current GTX 1080 users could scale their setup beyond two GPUs.



NVIDIA does have a method to its madness; it's a gamble, but we expect it to pay off in the best interests of gamers. Unlike current-generation AMD GPUs with XDMA CrossFire, which relies on the PCI-Express system bus for inter-GPU communication (which is pretty much also how DirectX 12 native multi-GPU tech works), NVIDIA continues to rely on a direct physical connection between GPUs for some inter-GPU communication. It's not that the PCI-Express bus doesn't have the bandwidth to cope with this sort of thing, but it adds latency. For a primary GPU to receive data from other GPUs in the machine, data must flow between those GPUs and the PCIe root complex, the CPU, and back down to the primary GPU. This creates some latency. SLI, on the other hand, does this by its direct connection. NVIDIA GPUs still use PCI-Express for "some" inter-GPU communication, but NVIDIA won't tell anyone what moves between PCIe and what moves over these bridges.



According to this NVIDIA graphic, the classic SLI bridge was proving to be insufficient for smooth display output at some of the higher resolutions (4K @ 60 Hz, 4K @ 120 Hz, 5K, and HDR-enabled resolutions). You can still very much use a classic 2-way bridge between two GTX 1080 cards, but NVIDIA claims that the performance won't be up to the mark. This is where the new SLI HB bridge steps in.

The SLI HB bridge taps into two SLI connectors and runs at a higher clock speed, providing sufficient bandwidth to link two GPUs for smooth output at the high resolutions we mentioned earlier. Since it eats up both SLI fingers on your card, you're limited to 2-way SLI. This is probably also why NVIDIA isn't supporting 3-way and 4-way SLI, knowing that people will use the 3-way and 4-way bridges that came with their motherboards that link each GPU to the next with just one path, which results in less than smooth output. The company even claims that this could have a negative impact on performance (vs. 2-way SLI).

So now, we have with us two GeForce GTX 1080 cards and an SLI HB bridge to present our GeForce GTX 1080 SLI review. We also had a classic 2-way bridge lying around, so we thought "why not throw in those numbers, too."

A Closer Look at the SLI HB Bridge

Unlike AMD, which used to bundle CrossFire bridge cables with its graphics cards before going cable-free with XDMA CrossFire, the new SLI HB bridge won't be included with every GTX 1080 or GTX 1070 graphics card. Some premium custom-design cards may have it as a part of a "premium accessory kit," but for most consumers, the bridge has to be purchased separately. You can still use the classic SLI bridge that came with your motherboard, though.


We have with us an NVIDIA-branded SLI HB bridge. It comes in three sizes depending on the spacing you want between your cards. The bridge is not flexible.


You get variants with 2-slot (zero-slot gap between two dual-slot graphics cards), 3-slot (one-slot gap between two dual-slot cards), and 4-slot spacing (two-slot gap between two dual-slot cards). The 2-slot variant should help with micro-ATX builds, 3-slot with most typical motherboards that have two slots between their two x16 slots, and 4-slot with certain LGA2011v3 HEDT boards that have x16 slots (electrical x16) 3 slots apart. We have the 3-slot variant with us today.


The SLI HB bridge, which uses a rock-solid metal case, reveals a rigid fiberglass PCB with two SLI slots wired along its length when taken apart. Each slot is reinforced with a metal sheath, much like PCI-Express x16 slots are in some of the newer motherboards. The bridge isn't just two classic bridges fused into one, though. It has a green LED that lights up only when SLI is enabled at the driver-level. On custom-design SLI HB bridges by NVIDIA partners, LEDs of different colors are available. Some even have RGB LEDs with manual color selection.


As mentioned earlier, you can use the classic 2-way bridge included with your motherboard, and NVIDIA's driver will enable SLI for you, but with a reminder that you can improve your experience with a "higher performance SLI bridge." This reminder goes away as soon as a SLI HB bridge is installed.

Test System

Benchmark scores in other reviews are only comparable when this exact same configuration is used.

• All video card results are obtained on this exact system with exactly the same configuration.
• 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:

• 1600x900: Common resolution for most smaller flatscreens and laptops today (17" - 19").
• 1920x1080: Most common widescreen resolution for larger displays (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.