NVLINK SLI / Overclocking Scanner and connectors

NVLINK and SLI

Is SLI back? Well, SLI has never been gone. But it got limited to two cards over the years, and driver optimization wise, things have not been optimal. If you have seen the PCB shots, you will have noticed a new sort of SLI finger, that is actually an NVLINK interface, and it's hot stuff.

NVLINK could have been used for a lot of other features, however is used just for SLI, so in essence it’s really simple. NVIDIA could/might have used NVLink for a lot of things other than SLI, but instead it is 100% similar to what SLI was, is and will be, just with far more bandwidth available over the interconnect. Think of NVLINK as SLI version three. It is just an interface yet many times faster.

For the RTX series, the link is going to be a 50 or 100 GB/sec interface, which is massive in terms of interconnects. We can't compare it 1:1 like that, but SLI or SLI HB passed 1 or 2 GB/sec respectively. One PCIe Gen 3 single lane offers 1 Gb/s, that's 16 GB/sec or 32 GB/sec full duplex. NVIDIA will support 2-way NVLINK. Currently, only the GeForce RTX 2080 and 2080 Ti will get NVLINK support and that physical connector will be present on those cards. The RTX 2070 and presumably future lower positioned models will not get this super fast multi-GPU interconnect.

NVLINK bridges are going to cost a spicy 79 bucks, you get 50 GB/sec on the RTX 2080 and 100 GB/sec on the GeForce RTX 2080 Ti. You will need some spacing between two cards, so there will be a 3-slot and 4-slot versions of the NVLINK connector available and, remember, there is a 2-way SLI maximum.

New OC Scanner

NVIDIA has been updating NVAPI - NVIDIA is including the NV Scanner API for the developers. You might have seen an example from EVGA already. I can tell you that for MSI Afterburner we're also developing the scanner functionality.

So what does it do? Basically, the scanner offers automated overclocking. At certain intervals and voltage frequency curves, the scanner will try to determine a stable overclock, this is presented in a curve and that curve can be applied for your tweak. The registers and variables are defined by NVIDIA, ergo you will only see very small performance increases by using the new feature. But with combined manual tweaks it will yield some nice results. This scanner needs to run for 10 to 20 minutes. For the novice with two left hands, it's an extra free 5% or whatever the final value will be. All popular overclocking tools from all brands can make use of it, and we assume that most of them will. We'll check this out later in the article.

Display connectors and video processing

Let's talk a little about updates to display connectivity as well as the video en/decoder. First and foremost, what you are going to notice is that the traditional DVI port is missing, at least on the Founders edition cards. This, we think, will be the same for most board partner cards. That means you'll get HDMI and Displayport. DisplayPort will be DP 1.4a ready and can support 8K60 in HDR, that's a resolution of 7680×4320 at 60 Hz and 10-bit HDR. HDMI is at 2.0b, which allows bandwidth up to 18Gbps 4K@50/60 (2160p). Also new is a small USB connector being present at the display connector side, this is for future VR solutions and is called VirtualLink. VirtualLink is a USB-C alternate mode that allows the power, video, and data required to power virtual reality headsets to be delivered over a single USB-C cable and connector instead of a set of three different cables as it was in older headsets. In VirtualLink mode there are six high-speed lanes active in the USB-C connector and cable: 4 lanes are used to transmit four DisplayPort HBR 3 video streams from PC to headset, and two lanes are used to implement bidirectional USB 3.1 Gen 2 channels between PC and headset. VirtualLink also requires the PC to provide from 15 up to 27 Watts of power.

The video processor has also had a bit of an update and offers an improved video and hardware en/decoder. HEVC 8K30 HDR real-time sees 25% bitrate savings. H.264 up to 15% bitrate savings. Turing GPUs can drive two 8K displays at 60 Hz with one cable for each display. Turing’s new display engine supports HDR processing natively in the display pipeline. Tone mapping has also been added to the HDR pipeline. Tone mapping is a technique used to approximate the look of high dynamic range images on standard dynamic range displays. Turing supports the tone mapping formula defined by the ITU-R Recommendation BT.2100 standard to avoid color shift on different HDR displays. Turing GPUs also ship with an enhanced NVENC encoder unit that adds support for H.265 (HEVC) 8K encode at 30 fps. The new NVENC encoder provides up to 25% bitrate savings for HEVC and up to 15% bitrate savings for H.264. Turing’s new NVDEC decoder has also been updated to support decoding of HEVC YUV444 10/12b HDR at 30 fps, H.264 8K, and VP9 10/12b HDR.