Scalable Link Interface

Last updated
Scalable Link Interface
NVidia SLI Logo.png
Manufacturer Nvidia
TypeMulti-GPU technology
Release date2004
Predecessor Scan-Line Interleave
Successor NVLink

Scalable Link Interface (SLI) is the brand name for a now discontinued multi-GPU technology developed by Nvidia for linking two or more video cards together to produce a single output. SLI is a parallel processing algorithm for computer graphics, meant to increase the available processing power. [1]

Contents

The initialism SLI was first used by 3dfx for Scan-Line Interleave, which was introduced to the consumer market in 1998 and used in the Voodoo2 line of video cards. [2] [3] [4] [5] After buying out 3dfx, Nvidia acquired the technology [6] [7] but did not use it. Nvidia later reintroduced the SLI name in 2004 and intended for it to be used in modern computer systems based on the PCI Express (PCIe) bus; however, the technology behind the name SLI has changed dramatically.

Implementation

SLI allows two, three, or four graphics processing units (GPUs) to share the workload when rendering real-time 3D computer graphics. Ideally, identical GPUs are installed on the motherboard that contains enough PCI Express slots, set up in a master–slave configuration. All graphics cards are given an equal workload to render, but the final output of each card is sent to the master card via a connector called the SLI bridge. For example, in a two graphics card setup, the master works on the top half of the scene, the slave the bottom half. Once the slave is done, it sends its render to the master to combine into one image before sending it to the monitor.

The SLI bridge is used to reduce bandwidth constraints and send data between both graphics cards directly. It is possible to run SLI without using the bridge connector on a pair of low-end to mid-range graphics cards (e.g., 7100GS or 6600GT) with Nvidia's Forceware drivers 80.XX or later. Since these graphics cards do not use as much bandwidth, data can be relayed through just the chipsets on the motherboard. However, if there are two high-end graphics cards installed and the SLI bridge is omitted, the performance will suffer severely, as the chipset does not have enough bandwidth.

Configurations include:

Nvidia has created a set of custom video game profiles in cooperation with video game publishers that will automatically enable SLI in the mode that gives the largest performance boost.

Nvidia has three types of SLI bridges:

The standard bridge is traditionally included with motherboards that support SLI and is recommended for monitors up to 1920×1080 and 2560×1440 at 60 Hz. The LED bridge is sold by Nvidia, [12] EVGA, [13] and others and is recommended for monitors up to 2560×1440 at 120 Hz and above and 4K. The LED bridges can only function at the increased pixel clock if the GPU supports that clock. The high-bandwidth bridge is only sold by Nvidia [14] and is recommended for monitors up to 5K and surround.

The following table provides an overview on the maximum theoretical bandwidth for data transfers depending on bridge type specifications as found on the open market: [15]

Clock rate400 MHz540 MHz650 MHz
single channel1 GB/s1.35 GB/s1.625 GB/s
dual channel2 GB/s2.7 GB/s3.25 GB/s

SLI modes

Split-frame rendering (SFR)

This analyzes the rendered image in order to split the workload equally between the two GPUs. To do this, the frame is split horizontally in varying ratios depending on geometry. For example, in a scene where the top half of the frame is mostly empty sky, the dividing line will lower, balancing geometry workload between the two GPUs.

Alternate-frame rendering (AFR)

Each GPU renders entire frames in sequence. For example, in a two-way setup, one GPU renders the odd frames, the other the even frames, one after the other. Finished outputs are sent to the master for display. Ideally, this would result in the rendering time being cut by the number of GPUs available. In their advertising, Nvidia claims up to 1.9 times the performance of one card with the two-way setup. While AFR may produce higher overall framerates than SFR, it also exhibits the temporal artifact known as micro stuttering, which may affect frame rate perception. It is noteworthy that while the frequency at which frames arrive may be doubled, the time to produce the frame is not reduced – which means that AFR is not a viable method of reducing input lag.

SLI antialiasing

This is a standalone rendering mode that offers up to double the antialiasing performance by splitting the antialiasing workload between the two graphics cards, offering superior image quality. One GPU performs an antialiasing pattern which is slightly offset to the usual pattern (for example, slightly up and to the right), and the second GPU uses a pattern offset by an equal amount in the opposite direction (down and to the left). Compositing both the results gives higher image quality than is normally possible. This mode is not intended for higher frame rates, and can actually lower performance, but is instead intended for games which are not GPU-bound, offering a clearer image in place of better performance. When enabled, SLI antialiasing offers advanced antialiasing options: SLI 8×, SLI 16×, and SLI 32× (for quad SLI systems only). [16]

Hybrid SLI

Hybrid SLI is the generic name for two technologies, GeForce Boost and HybridPower. [17]

GeForce Boost allows the rendering power of an integrated graphics processor (IGP) and a discrete GPU to be combined in order to increase performance. [17]

HybridPower, on the other hand, is another mode that is not for performance enhancement. The setup consists of an IGP as well as a GPU on MXM module. The IGP would assist the GPU to boost performance when the laptop is plugged to a power socket while the MXM module would be shut down when the laptop was unplugged from power socket to lower overall graphics power consumption. [18] [19] Hybrid SLI is also available on desktop Motherboards and PCs with PCI-E discrete video cards. NVIDIA claims that twice the performance can be achieved with a Hybrid SLI capable IGP motherboard and a GeForce 8400 GS video card. [20] [21]

HybridPower was later renamed as Nvidia Optimus.

SLI HB

In May 2016 Nvidia announced that the GeForce 10 series would feature a new SLI HB (High Bandwidth) bridge; this bridge uses 2 SLI fingers on the PCB of each card and essentially doubles the available bandwidth between them. Only GeForce 10 series cards support SLI HB [22] [23] and only 2-way SLI is supported over this bridge for single-GPU cards. [22] SLI HB interface runs at 650 MHz, while legacy SLI interface runs at slower 400 MHz. [24]

Electrically there is little difference between the regular SLI bridge and the SLI HB bridge. It is similar to two regular bridges combined in one PCB. The signal quality of the bridge improved, however, as the SLI HB bridge has an adjusted trace-length to make sure all traces on the bridge have exactly the same length. [24]

A PC gaming magazine did a comparison between SLI bridges and their SLI HB successors with X-rays, and found differences in the PCB tracing allowed clock rates to go up from 400 MHz to 650 MHz and thus the data rates along with that. With the increased bus width a noticeable bandwidth increase should be expected; however tests with a GTX 1080 GPU showed the improvements in gaming performance were marginal. Newer HB bridges are LED illuminated (often back-side-illuminating some logo) and as a result more costly than earlier bridges at a comparable base functionality. [25]

Caveats

See also

Related Research Articles

<span class="mw-page-title-main">Accelerated Graphics Port</span> Expansion bus standard

Accelerated Graphics Port (AGP) is a parallel expansion card standard, designed for attaching a video card to a computer system to assist in the acceleration of 3D computer graphics. It was originally designed as a successor to PCI-type connections for video cards. Since 2004, AGP was progressively phased out in favor of PCI Express (PCIe), which is serial, as opposed to parallel; by mid-2008, PCI Express cards dominated the market and only a few AGP models were available, with GPU manufacturers and add-in board partners eventually dropping support for the interface in favor of PCI Express.

<span class="mw-page-title-main">Graphics card</span> Expansion card which generates a feed of output images to a display device

A graphics card is a computer expansion card that generates a feed of graphics output to a display device such as a monitor. Graphics cards are sometimes called discrete or dedicated graphics cards to emphasize their distinction to an integrated graphics processor on the motherboard or the central processing unit (CPU). A graphics processing unit (GPU) that performs the necessary computations is the main component in a graphics card, but the acronym "GPU" is sometimes also used to erroneously refer to the graphics card as a whole.

<span class="mw-page-title-main">GeForce</span> Brand of GPUs by Nvidia

GeForce is a brand of graphics processing units (GPUs) designed by Nvidia and marketed for the performance market. As of the GeForce 40 series, there have been eighteen iterations of the design. The first GeForce products were discrete GPUs designed for add-on graphics boards, intended for the high-margin PC gaming market, and later diversification of the product line covered all tiers of the PC graphics market, ranging from cost-sensitive GPUs integrated on motherboards, to mainstream add-in retail boards. Most recently, GeForce technology has been introduced into Nvidia's line of embedded application processors, designed for electronic handhelds and mobile handsets.

<span class="mw-page-title-main">Graphics processing unit</span> Specialized electronic circuit; graphics accelerator

A graphics processing unit (GPU) is a specialized electronic circuit initially designed for digital image processing and to accelerate computer graphics, being present either as a discrete video card or embedded on motherboards, mobile phones, personal computers, workstations, and game consoles. After their initial design, GPUs were found to be useful for non-graphic calculations involving embarrassingly parallel problems due to their parallel structure. Other non-graphical uses include the training of neural networks and cryptocurrency mining.

<span class="mw-page-title-main">GeForce 6 series</span> Series of GPUs by Nvidia

The GeForce 6 series is the sixth generation of Nvidia's GeForce line of graphics processing units. Launched on April 14, 2004, the GeForce 6 family introduced PureVideo post-processing for video, SLI technology, and Shader Model 3.0 support.

<span class="mw-page-title-main">Alienware</span> American computer hardware subsidiary of Dell Inc.

Alienware Corporation is an American computer hardware subsidiary brand of Dell. Their product range is dedicated to gaming computers and accessories and can be identified by their alien-themed designs. Alienware was founded in 1996 by Nelson Gonzalez and Alex Aguila. The development of the company is also associated with Frank Azor, Arthur Lewis, Joe Balerdi, and Michael S. Dell (CEO). The company's corporate headquarters is located in The Hammocks, Miami, Florida.

nForce4 Motherboard chipset

The nForce4 is a motherboard chipset released by Nvidia in October 2004. The chipset supports AMD 64-bit processors and Intel Pentium 4 LGA 775 processors.

<span class="mw-page-title-main">Voodoo 5</span> Graphics card line

The Voodoo 5 was the last and most powerful graphics card line that was released by 3dfx Interactive. All members of the family were based upon the VSA-100 graphics processor. Only the single-chip Voodoo 4 4500 and dual-chip Voodoo 5 5500 made it to market.

<span class="mw-page-title-main">Dell XPS</span> Line of high performance computers manufactured by Dell

Dell XPS is a line of consumer-oriented laptop and desktop computers manufactured by Dell since 1993.

<span class="mw-page-title-main">AMD CrossFire</span> Brand name by AMD; multi-GPU technology

AMD CrossFire is a brand name for the multi-GPU technology by Advanced Micro Devices, originally developed by ATI Technologies. The technology allows up to four GPUs to be used in a single computer to improve graphics performance.

<span class="mw-page-title-main">GeForce 7 series</span> Series of GPUs by Nvidia

The GeForce 7 series is the seventh generation of Nvidia's GeForce line of graphics processing units. This was the last series available on AGP cards.

The GeForce 8 series is the eighth generation of Nvidia's GeForce line of graphics processing units. The third major GPU architecture developed by Nvidia, Tesla represents the company's first unified shader architecture.

The nForce 600 chipset was released in the first half of November 2006, coinciding with the GeForce 8 series launch on November 8, 2006. The nForce 600 supports Intel's LGA 775 socket and AMD's Quad FX platform and replaces the nForce 500 series.

The GeForce 9 series is the ninth generation of Nvidia's GeForce line of graphics processing units, the first of which was released on February 21, 2008. The products are based on an updated Tesla microarchitecture, adding PCI Express 2.0 support, improved color and z-compression, and built on a 65 nm process, later using 55 nm process to reduce power consumption and die size.

nForce 700 Chipset series by Nvidia

The nForce 700 is a chipset series designed by Nvidia first released in December 2007. The series supports both Intel Core 2 and AMD Phenom processors, and replaces the nForce 600 series chipsets. Several members were spotted, including the codenamed MCP72 for AMD processors and the C72 for Intel processors, launched with the name "nForce 780a" and "nForce 780i" chipsets respectively. Currently, the released variants are the 750i, 780i, 790i, and 790i Ultra.

<span class="mw-page-title-main">GPU switching</span> Mechanism for computers with multiple graphic controllers

GPU switching is a mechanism used on computers with multiple graphic controllers. This mechanism allows the user to either maximize the graphic performance or prolong battery life by switching between the graphic cards. It is mostly used on gaming laptops which usually have an integrated graphic device and a discrete video card.

EVGA Corporation is an American computer hardware company that produces motherboards, gaming laptops, power supplies, all-in-one liquid coolers, computer cases, and gaming mice. Founded on April 13, 1999, its headquarters are in Brea, California. EVGA also produced Nvidia GPU-based video cards until 2022.

The GeForce 700 series is a series of graphics processing units developed by Nvidia. While mainly a refresh of the Kepler microarchitecture, some cards use Fermi (GF) and later cards use Maxwell (GM). GeForce 700 series cards were first released in 2013, starting with the release of the GeForce GTX Titan on February 19, 2013, followed by the GeForce GTX 780 on May 23, 2013. The first mobile GeForce 700 series chips were released in April 2013.

<span class="mw-page-title-main">NVLink</span> High speed chip interconnect

NVLink is a wire-based serial multi-lane near-range communications link developed by Nvidia. Unlike PCI Express, a device can consist of multiple NVLinks, and devices use mesh networking to communicate instead of a central hub. The protocol was first announced in March 2014 and uses a proprietary high-speed signaling interconnect (NVHS).

<span class="mw-page-title-main">Pascal (microarchitecture)</span> GPU microarchitecture by Nvidia

Pascal is the codename for a GPU microarchitecture developed by Nvidia, as the successor to the Maxwell architecture. The architecture was first introduced in April 2016 with the release of the Tesla P100 (GP100) on April 5, 2016, and is primarily used in the GeForce 10 series, starting with the GeForce GTX 1080 and GTX 1070, which were released on May 27, 2016, and June 10, 2016, respectively. Pascal was manufactured using TSMC's 16 nm FinFET process, and later Samsung's 14 nm FinFET process.

References

  1. ↑ "What is SLI?". www.geforce.com. Retrieved 24 November 2014.
  2. ↑ "3Dfx Voodoo2". Next Generation . No. 37. Imagine Media. January 1998. pp. 88–92.
  3. ↑ Sanchez, Andrew (January 1998). "Previews – 3Dfx Voodoo2". boot . No. 17. pp. 86–87.
  4. ↑ Lal Shimpi, Anand. 3dfx Voodoo5 5500, Anandtech, July 11, 2000.
  5. ↑ 3dfx Interview with Peter Wicher, Hot Hardware, December 15, 2001.
  6. ↑ SEC filings, Form 8-K: Bankruptcy or receivership Archived August 27, 2017, at the Wayback Machine , updated October 21, 2002, retrieved August 28, 2024
  7. ↑ "3dfx Announces Three Major Initiatives To Protect Creditors and Maximize Shareholder Value". December 15, 2000. Archived from the original on April 5, 2001. Retrieved August 28, 2024.
  8. ↑ "[EVGA] New Pro SLI Bridges V2". Overclock.net. 22 February 2016.
  9. ↑ "SLI - FAQ - GeForce". www.geforce.com.
  10. ↑ "[EVGA] New Pro SLI Bridges V2". Overclock.net. 22 February 2016.
  11. ↑ "Nvidia GeForce GTX 1080 Pascal Display Pipeline & SLI". 17 May 2016.
  12. ↑ "NVIDIA SLI Bridges - GeForce". www.geforce.com.
  13. ↑ "EVGA - Articles - EVGA Pro SLI Bridges V2". EVGA.
  14. ↑ "GeForce GTX 1080 Graphics Cards from NVIDIA GeForce". Nvidia.
  15. ↑ "Nvidia HB-SLI-Brücke: Unterschiede anhand von Röntgenbildern gezeigt" (in German). 12 August 2016.
  16. ↑ "Introducing SLI Antialiasing: The Ultimate in Visual Quality". Nvidia. Retrieved 24 November 2014.
  17. 1 2 "Hybrid SLI Technology". Nvidia. Retrieved 23 March 2015.
  18. ↑ Valich, Theo (2007-06-26). "NVIDIA's Hybrid SLI attacks AMD's PowerXPress". The Inquirer. Archived from the original on 2007-10-04. Retrieved 2007-09-26.{{cite news}}: CS1 maint: unfit URL (link)
  19. ↑ Shilov, Anton (2007-06-25). "NVIDIA Readies Hybrid SLI Technology". X-bit labs. Retrieved 2007-10-17.
  20. ↑ Abazovic, Faud (2007-08-08). "Hybrid SLI first for AMD". Archived from the original on 2007-11-14. Retrieved 2007-10-17.
  21. ↑ "Growth Opportunities" (PDF). NVIDIA. 2007-06-20. p. 9. Retrieved 2007-10-17.
  22. 1 2 W1zzard (May 17, 2016). "Nvidia GeForce GTX 1080 8 GB". TechPowerUp. Archived from the original on 2016-05-21. Retrieved August 28, 2024.{{cite web}}: CS1 maint: numeric names: authors list (link)
  23. 1 2 "NVIDIA GeForce RTX 2080 Founders Edition Graphics Card". NVIDIA. Retrieved 2018-08-31.
  24. 1 2 "NVIDIA HB SLI Bridge: A Technical Review - Overclocking.Guide". 2016-08-11. Archived from the original on 2016-09-09. Retrieved 2016-08-11.
  25. ↑ "Nvidia HB-SLI-Brücke: Unterschiede anhand von Röntgenbildern gezeigt". 12 August 2016.
  26. ↑ "NVIDIA SLI Technology Now Licensed For INTEL Core I7 And Core I5 Platforms".
  27. ↑ "Motherboards". NVIDIA. Retrieved 2016-05-16.
  28. 1 2 "SLI FAQs". NVIDIA. Retrieved 2008-12-04.
  29. ↑ Kreiss, Tino; Töpelt, Bert; Schuhmann, Daniel (2005-12-02). "Performance Comparison Between Single Configurations And SLI Setups". Tom's Hardware . Retrieved 2007-06-01.
  30. ↑ Bit-Tech interview (page 2), retrieved January 23, 2008
  31. ↑ Raffael Vötter (2008-02-08). "Video proof: Micro stuttering may destroy the performance gains from current multi GPU technologies". PC Games Hardware Online. Retrieved 2009-11-03.
  32. ↑ "nVidia drops SLI support (multi-GPU) for its GeForce RTX 3000-Series graphics cards". TechReportArticles. 6 Sep 2020.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.