Scalable Link Interface
Encyclopedia
Scalable Link Interface (SLI) is a brand name for a multi-GPU
solution developed by NVIDIA
for linking two or more video card
s together to produce a single output. SLI is an application of parallel processing
for computer graphics, meant to increase the processing power available for graphics.
The name SLI was first used by 3dfx
under the full name Scan-Line Interleave
, which was introduced to the consumer market in 1998 and used in the Voodoo2
line of video cards. After buying out 3dfx, NVIDIA acquired the technology 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.
s (GPUs) to share the workload when rendering a frame. Ideally, two cards using identical GPUs are installed in a motherboard that contains two PCI-Express slots, set up in a master-slave configuration. Both cards are given the same part of the 3D scene to render, but effectively half of the work load is sent to the master card through a connector called the SLI Bridge. As an example, the master card works on the top half of the scene while the slave card works on the bottom half. When the slave card is done, it sends its output to the master card, which combines the two images to form one and then outputs the final render to the monitor.
In its early implementations, motherboard
s capable of SLI required a special card ("paddle card") which came with the motherboard. This card would fit into a socket usually located between both of the PCI-Express x16 slots. Depending on which way the card was inserted, the motherboard would either channel all 16 lanes into the primary PCI-Express x16 slot, or split lanes equally to both PCI-Express x16 slots (i.e. 8 lanes per slot). This was necessary as no motherboard at that time had enough PCI-Express lanes for both to have 16 lanes each. With the increase in available PCI-Express lanes, most modern SLI-capable motherboards allow each video card to use all 16 lanes in both PCI-Express x16 slots.
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 no SLI bridge is used on two high-end graphics cards, the performance suffers severely as the chipset does not have enough bandwidth.
SLI offers two rendering and one anti-aliasing
method for splitting the work between the video cards:
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. It is also possible to create custom game profiles or modify pre-defined profiles using their Coolbits software.
For more information on SLI-optimized games, visit NVIDIA's SLI Zone.
released the GV-3D1, a single video card that uses NVIDIA's SLI technology to run two 6600-series GPUs
. Due to technical issues with compatibility, at release the card was supported by only one of Gigabyte's own motherboards, with which it was bundled. Later came the GV-3D1-68GT, functionally similar and possessing similarly-limited motherboard compatibility, but with 6800 GPUs in place of the GV-3D1's 6600 units.
Around March 2006, ASUS
released the N7800GT Dual. Similar to Gigabyte's design, it had two 7800GT GPUs mounted on one video card. Again, this faced several issues, such as pricing (it retailed for around US$800, while two separate 7800GTs were cheaper at the time), limited release, and limited compatibility. It would only be supported on the nForce4
chipset and only a few nForce4 chipset-based motherboards could actually utilize it. It was also one of the first video cards with the option to use an external power supply
if needed.
In January 2006, NVIDIA released the 7900 GX2, their own attempt at a dual-GPU card. Effectively, this product is a pair of slightly lower clocked 7900GTX cards "bridged" together into one discrete unit, with separate frame buffers for both GPUs (512MB of GDDR3 each). The GeForce 7900 GX2 is only available to OEM companies for inclusion in quad-GPU systems, and it cannot be bought in the consumer market. The Dell XPS, announced at the 2006 Consumer Electronics Show
, used two 7900 GX2's to build a quad-GPU system. Later, Alienware
acquired the technology in March.
The official implementations of dual-GPU graphics cards work in the same fashion. Two GPUs are placed on two separate printed circuit boards (PCBs
), with their own power circuitry and memory. Both boards have slim coolers, cooling the GPU and memory. The 'primary' GPU can be considered to be the one on the rear board, or 'top' board (being on top when in a standard ATX system). The primary board has a physical PCIe x16 connector, and the other has a round gap in it to provide cooling for the primary HSF. Both boards are connected to each other by two physical links; one for 16 PCI-Express lanes, and one for the 400 MHz SLI bridge. An onboard PCI-Express bridge chip, with 48 lanes in total, acts as the MCP does in SLI motherboards, connecting to both GPUs and the physical PCI-Express slot, removing the need for the motherboard to support SLI.
A newer version, the GeForce 7950 GX2, which addressed many issues in the 7900 GX2, was available to consumers for separate purchase.
The GeForce 9800 GX2 was NVIDIA's next attempt at a multi-GPU solution released in March 2008, this time using separate PCBs facing each other, thus sharing one large double wide cooling fan. This GX2 could expand to a total of four GPUs when paired in SLI. The 9800 GX2 was concurrent with the launch of a single-GPU 65 nm 9800 GTX. Three months later, with the 9800 GX2 selling at $299, NVIDIA found their product line competing with itself, as the GTX 260 and the 55 nm improved 9800 GTX+ became available, NVIDIA elected to venture into the GTX200 series and beyond lineups, rather than expanding the 55 nm G92 into a GX2 form factor, thus leaving mid-range audiences with the options of the 9800 GT and 9800 GTX+.
On January 2009, the new GTX200 series based GeForce GTX 295 was released. It combines two 55 nm GeForce GTX 275 GPUs underclocked, with a similar sandwich design of two graphics PCBs facing each other with a large double wide cooling fan solution in-between, but with all the GDDR3 RAM modules on the same half of each board as each corresponding GPU; a feature that neither the initial GTX200 boards nor the 9800 GX2 board had. It manages to maintain the same amount of shaders as the GTX 280/285 bringing it to a total of 480 shader units. A second version of the GTX295 has been produced, this time using a single PCB and a dual slot cooler.
Nvidia introduced its own new flagship video card, the GeForce GTX 590 - Nvidia's first dual-GPU video card since the GTX 295 in early 2009. The GTX 590 unites a pair of GF110 GPUs (similar to the ones used in the GTX 580, the fastest single-GPU card on the market) on a single card. This translates to 1,024 CUDA processing cores, 128 texture units, 96 ROP units, and 32 tessellation engines. The card's graphics clock runs at 607 MHz, its processor clock at 1,215 MHz, and its memory clock at 3,414 MHz. It is loaded with 3,072MB of GDDR5 memory for the frame buffer, which operates over a 384-bit memory interface.
Quad SLI did not show any massive improvements in gaming using the common resolutions of 1280×1024 and 1600×1200, but has shown improvements by enabling 32x anti-aliasing
in SLI-AA mode, and support for 2560×1600 resolutions at much higher framerates than is possible with single or dual GPU systems with maximum settings in modern games. It was believed that high latencies severely marginalized the benefits of four GPUs, however much of the blame for poor performance scaling is due to Windows XP's API which only allows for a maximum storage of 3 extra frames. Windows Vista and Windows 7 are not limited in this fashion and shows promise for future multi-GPU configurations.
In March 2008, NVIDIA released the GeForce 9800 GX2 GPU. Targeted at high-end gaming, the 9800 GX2 is essentially two updated and slightly underclocked G92 8800GTS cores on a dual-PCB graphics card to compete with ATI's HD 3870×2. Though NVIDIA did not release Quad SLI drivers for the 9800 GX2 at time of release, the telltale SLI connector on the top of the card leaves little doubt that users in the future will be able to equip themselves with two 9800GX2s, thus allowing for a total of 4 GPUs in one system via only 2 PCI Express x16 graphics slots, a feat impossible since the 7950GX2. Note that NVIDIA no longer supports Quad SLI on Windows XP (NVIDIA will automatically prevent you from using two 9800GX2s without Windows Vista.)
Currently, the only GPUs that can support 4-way SLI are the GTX 480 and GTX 580, and they must be used on an Intel x58 or 5520 chipset combined with a Nvidia nForce 200 chipset, to provide extra PCI lanes.
series motherboards, which only works on Windows Vista. The X58 intel chipset also implement 3-way SLI using an additional NF200 component based on nForce 700
. The setup can be achieved using three high-end video cards with two MIO ports and a specially wired connector (or three flexible connectors used in a specific arrangement).
The technology was officially announced in December 2007, shortly after the revised G92-based 8800GTS made its way out of the factory. In practical terms, it delivers up to a 2.8x performance increase over a single GPU system.
3-Way SLI is possible using all GeForce GTX except GTX 295 and GTX 460 (580, 570, 480, 470, 465, 285, 280, 275, 260). The GeForce GTX 295 does not support 3-way SLI but supports 4-way SLI and Multi-GPU. The 460 GTX was rumoured to support 3-Way SLI but upon release people found the 1 toothed 2-Way SLI bridge, this is because the 460 was not meant to replace the 260, it was supposed to push up the rest of NVIDIA's product line and make the 465 GTX more appealing, but due to heat issues 465 GTX's were considered flops and the mass of gamers stuck with 2-Way SLI 460 GTX.
Unlike traditional SLI, or CrossFireX
, 3-way SLI was limited to the GeForce
8800 GTX, 8800 Ultra, 9800 GTX and June 2008 introduced the GTX 260, GTX 280, the 9800 GTX+ and also the GTX 275, 285, 465, 470 and 480 graphic cards on the 680i, 780i 790i, certain P55 chipsets, X58 chipsets, whereas CrossFireX can be theoretically used on multiple ATI (now AMD) Radeon cards (up to 4-GPUSs, must have same core irrespective of product binning).
Visual Computing System is an external graphics processing unit
designed for large-scale 3D
visualizations. The system consists of a box containing a pair of high-end NVIDIA
graphics cards featuring a variety of external video connectors. A special PCI Express
card is installed in the host computer, and the two are connected by VHDCI
cables.
The NVIDIA Quadro Plex system supports up to four GPU
s per unit. It connects to the host PC via a small form factor PCI Express
card connected to the host, and a 2 meter (6.5 foot) NVIDIA Quadro Plex Interconnect Cable. The system is housed in an external case that is approximately 9.5 inches high, 6 inches wide, and 20.6 inches in depth and weighs about 19 pounds. The system relies heavily on NVIDIA's SLI technology.
offering a discrete physics calculation solution in a tri-GPU system, NVIDIA announced a partnership with physics middleware
company Havok
to incorporate a similar system using a similar approach. Although this would eventually become the Quantum Effects technology, many motherboard companies began producing boards with three PCI-Express x16 slots in anticipation of this implementation being used.
In February 2008, NVIDIA acquired physics hardware and software firm Ageia, with plans to increase the market penetration for PhysX beyond its fairly limited use in games; notably Unreal Engine 3. In July 2008, NVIDIA released a beta PhysX
driver supporting GPU acceleration, followed by an official launch on August 12, 2008. This allows PhysX acceleration on the primary GPU, a different GPU, or on both GPUs in SLI.
In January 2009 Mirror's Edge
became the first major PC game title to add NVIDIA PhysX to enhance visual effects in-game and add gameplay elements.
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.
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.
On November 5, 2008 in Microsoft’s Guidelines for Graphics in Windows 7 document, Microsoft stated that Windows 7 will not offer native support for hybrid graphics systems. Microsoft added the reason for the decision saying that hybrid graphics systems ‘can be unstable and provide a poor user experience,’ and that it would ‘strongly discourage system manufacturers from shipping such systems.’ Microsoft also added that ‘such systems require a reboot to switch between GPUs.’
On desktop systems, the motherboard chipsets nForce 720a, 730a, 750a SLI, 780a SLI and 980a SLI and the motherboard GPUs GeForce 8100, 8200, 8300 and 9300 support Hybrid SLI (GeForce Boost and HybridPower). The GPUs GeForce 8400 GS and 8500 GT support GeForce Boost, the GPUs 9800 GT, 9800 GTX, 9800 GTX+ 9800 GX2, GTX 260 and GTX 280 support HybridPower.
Nevertheless, the most common cards which can be purchased nowadays do not support HybridPower, as manufacturer of the cards do not place the necessary PIC16F690 on the Graphic-PCB. Although for all users the switching is possible with tray icon, only a handful cardtypes have the ability to switch off the power completely.
There is Kernel level support in Linux as of 2.6.34 However user tools to actually use the feature are fairly primitive at this time.
Graphics processing unit
A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...
solution developed by NVIDIA
NVIDIA
Nvidia is an American global technology company based in Santa Clara, California. Nvidia is best known for its graphics processors . Nvidia and chief rival AMD Graphics Techonologies have dominated the high performance GPU market, pushing other manufacturers to smaller, niche roles...
for linking two or more video card
Video card
A video card, Graphics Card, or Graphics adapter is an expansion card which generates output images to a display. Most video cards offer various functions such as accelerated rendering of 3D scenes and 2D graphics, MPEG-2/MPEG-4 decoding, TV output, or the ability to connect multiple monitors...
s together to produce a single output. SLI is an application of parallel processing
Parallel computing
Parallel computing is a form of computation in which many calculations are carried out simultaneously, operating on the principle that large problems can often be divided into smaller ones, which are then solved concurrently . There are several different forms of parallel computing: bit-level,...
for computer graphics, meant to increase the processing power available for graphics.
The name SLI was first used by 3dfx
3dfx
3dfx Interactive was a company that specialized in the manufacturing of 3D graphics processing units and, later, graphics cards. It was a pioneer in the field for several years in the late 1990s until 2000 when it underwent one of the most high-profile demises in the history of the PC industry...
under the full name Scan-Line Interleave
Scan-Line Interleave
Scan-Line Interleave from 3dfx is a method for linking two video cards or chips together to produce a single output. It is an application of parallel processing for computer graphics, meant to increase the processing power available for graphics. SLI from 3dfx was introduced in 1998 and used in...
, which was introduced to the consumer market in 1998 and used in the Voodoo2
Voodoo2
The Voodoo2 was a set of three graphics processing units on a single chipset, made by 3dfx. It was released in February 1998 as a replacement for the original Voodoo Graphics chipset. The card ran at a chipset clock rate of 90 MHz and used 100 MHz EDO DRAM, and was available for the PCI interface...
line of video cards. After buying out 3dfx, NVIDIA acquired the technology 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
PCI Express
PCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...
(PCIe) bus; however, the technology behind the name SLI has changed dramatically.
Implementation
SLI allows two, three or four graphics processing unitGraphics processing unit
A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...
s (GPUs) to share the workload when rendering a frame. Ideally, two cards using identical GPUs are installed in a motherboard that contains two PCI-Express slots, set up in a master-slave configuration. Both cards are given the same part of the 3D scene to render, but effectively half of the work load is sent to the master card through a connector called the SLI Bridge. As an example, the master card works on the top half of the scene while the slave card works on the bottom half. When the slave card is done, it sends its output to the master card, which combines the two images to form one and then outputs the final render to the monitor.
In its early implementations, motherboard
Motherboard
In personal computers, a motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple...
s capable of SLI required a special card ("paddle card") which came with the motherboard. This card would fit into a socket usually located between both of the PCI-Express x16 slots. Depending on which way the card was inserted, the motherboard would either channel all 16 lanes into the primary PCI-Express x16 slot, or split lanes equally to both PCI-Express x16 slots (i.e. 8 lanes per slot). This was necessary as no motherboard at that time had enough PCI-Express lanes for both to have 16 lanes each. With the increase in available PCI-Express lanes, most modern SLI-capable motherboards allow each video card to use all 16 lanes in both PCI-Express x16 slots.
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 no SLI bridge is used on two high-end graphics cards, the performance suffers severely as the chipset does not have enough bandwidth.
SLI offers two rendering and one anti-aliasing
Anti-aliasing
In digital signal processing, spatial anti-aliasing is the technique of minimizing the distortion artifacts known as aliasing when representing a high-resolution image at a lower resolution...
method for splitting the work between the video cards:
- Split Frame Rendering (SFR), the first rendering method. This analyzes the rendered image in order to split the workload 50/50 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. This method does not scale geometry or work as well as AFR, however.
- Alternate Frame Rendering (AFR), the second rendering method. Here, each GPU renders entire frames in sequence – one GPU processes even frames, and the second processes odd frames, one after the other. When the slave card finishes work on a frame (or part of a frame) the results are sent via the SLI bridge to the master card, which then outputs the completed frames. Ideally, this would result in the rendering time being cut in half, and thus performance from the video cards would double. In their advertising, NVIDIA claims up to 1.9x the performance of one card with the dual-card setup. While AFR may produce higher overall framerates than SFR, it may result in increased input latency due to the next frame starting rendering in advance of the frame before it. This is identical to the issue that was first discovered in the ATI Rage Fury MAXX board in 1999. This makes SFR the preferred SLI method for fast paced action games.
- 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 8X, SLI 16X, and SLI 32x (only available on newer, higher-end models starting with the 8800 series). A Quad SLI system is capable of up to SLI 64X antialiasing.
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. It is also possible to create custom game profiles or modify pre-defined profiles using their Coolbits software.
For more information on SLI-optimized games, visit NVIDIA's SLI Zone.
Two GPUs on one PCI-E slot
In February 2005, Gigabyte TechnologyGigabyte Technology
Gigabyte Technology Co., Ltd. is a Taiwan-based manufacturer of computer hardware products best known for its motherboards. The company is publicly held and traded on the Taiwan Stock Exchange .-Company:...
released the GV-3D1, a single video card that uses NVIDIA's SLI technology to run two 6600-series GPUs
Graphics processing unit
A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...
. Due to technical issues with compatibility, at release the card was supported by only one of Gigabyte's own motherboards, with which it was bundled. Later came the GV-3D1-68GT, functionally similar and possessing similarly-limited motherboard compatibility, but with 6800 GPUs in place of the GV-3D1's 6600 units.
Around March 2006, ASUS
ASUS
ASUSTeK Computer Incorporated is a multinational computer technology and consumer electronics product manufacturer headquartered in Taipei, Taiwan. Its product range includes motherboards, desktops, laptops, monitors, tablet PCs, servers and mobile phones...
released the N7800GT Dual. Similar to Gigabyte's design, it had two 7800GT GPUs mounted on one video card. Again, this faced several issues, such as pricing (it retailed for around US$800, while two separate 7800GTs were cheaper at the time), limited release, and limited compatibility. It would only be supported on the nForce4
NForce4
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.-nForce4/nForce4-4x:...
chipset and only a few nForce4 chipset-based motherboards could actually utilize it. It was also one of the first video cards with the option to use an external power supply
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
if needed.
In January 2006, NVIDIA released the 7900 GX2, their own attempt at a dual-GPU card. Effectively, this product is a pair of slightly lower clocked 7900GTX cards "bridged" together into one discrete unit, with separate frame buffers for both GPUs (512MB of GDDR3 each). The GeForce 7900 GX2 is only available to OEM companies for inclusion in quad-GPU systems, and it cannot be bought in the consumer market. The Dell XPS, announced at the 2006 Consumer Electronics Show
Consumer Electronics Show
The International Consumer Electronics Show is a major technology-related trade show held each January in the Las Vegas Convention Center, Las Vegas, Nevada, United States. Not open to the public, the Consumer Electronics Association-sponsored show typically hosts previews of products and new...
, used two 7900 GX2's to build a quad-GPU system. Later, Alienware
Alienware
Alienware is an American computer hardware subsidary of Dell, Inc. It mainly assembles third party components into desktops and laptops with custom enclosures for high-performance gaming. These products also support graphically intense applications such as video editing, simulation, and audio editing...
acquired the technology in March.
The official implementations of dual-GPU graphics cards work in the same fashion. Two GPUs are placed on two separate printed circuit boards (PCBs
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
), with their own power circuitry and memory. Both boards have slim coolers, cooling the GPU and memory. The 'primary' GPU can be considered to be the one on the rear board, or 'top' board (being on top when in a standard ATX system). The primary board has a physical PCIe x16 connector, and the other has a round gap in it to provide cooling for the primary HSF. Both boards are connected to each other by two physical links; one for 16 PCI-Express lanes, and one for the 400 MHz SLI bridge. An onboard PCI-Express bridge chip, with 48 lanes in total, acts as the MCP does in SLI motherboards, connecting to both GPUs and the physical PCI-Express slot, removing the need for the motherboard to support SLI.
A newer version, the GeForce 7950 GX2, which addressed many issues in the 7900 GX2, was available to consumers for separate purchase.
The GeForce 9800 GX2 was NVIDIA's next attempt at a multi-GPU solution released in March 2008, this time using separate PCBs facing each other, thus sharing one large double wide cooling fan. This GX2 could expand to a total of four GPUs when paired in SLI. The 9800 GX2 was concurrent with the launch of a single-GPU 65 nm 9800 GTX. Three months later, with the 9800 GX2 selling at $299, NVIDIA found their product line competing with itself, as the GTX 260 and the 55 nm improved 9800 GTX+ became available, NVIDIA elected to venture into the GTX200 series and beyond lineups, rather than expanding the 55 nm G92 into a GX2 form factor, thus leaving mid-range audiences with the options of the 9800 GT and 9800 GTX+.
On January 2009, the new GTX200 series based GeForce GTX 295 was released. It combines two 55 nm GeForce GTX 275 GPUs underclocked, with a similar sandwich design of two graphics PCBs facing each other with a large double wide cooling fan solution in-between, but with all the GDDR3 RAM modules on the same half of each board as each corresponding GPU; a feature that neither the initial GTX200 boards nor the 9800 GX2 board had. It manages to maintain the same amount of shaders as the GTX 280/285 bringing it to a total of 480 shader units. A second version of the GTX295 has been produced, this time using a single PCB and a dual slot cooler.
Nvidia introduced its own new flagship video card, the GeForce GTX 590 - Nvidia's first dual-GPU video card since the GTX 295 in early 2009. The GTX 590 unites a pair of GF110 GPUs (similar to the ones used in the GTX 580, the fastest single-GPU card on the market) on a single card. This translates to 1,024 CUDA processing cores, 128 texture units, 96 ROP units, and 32 tessellation engines. The card's graphics clock runs at 607 MHz, its processor clock at 1,215 MHz, and its memory clock at 3,414 MHz. It is loaded with 3,072MB of GDDR5 memory for the frame buffer, which operates over a 384-bit memory interface.
Quad SLI
In early 2006, NVIDIA revealed its plans for Quad SLI. When the 7900GX2 was originally demonstrated, it was with two such cards in a SLI configuration. This is possible because each GX2 has two extra SLI connectors, separate from the bridges used to link the two GPUs in one unit – one on each PCB, two per GPU, for a total of two links per GPU. When two GX2 graphics cards are installed in a SLI motherboard, these SLI connectors are bridged using two separate SLI bridges. (In such a configuration, if the four PCBs were labeled A, B, C, D from top to bottom, A and C would be linked by an SLI bridge, as would B and D.) This way, four GPUs can contribute to performance. The 7950GX2, sold as an enthusiast-friendly card, omits the external SLI connector on one of its PCBs, meaning that only one SLI bridge is required to run two 7950GX2s in SLI.Quad SLI did not show any massive improvements in gaming using the common resolutions of 1280×1024 and 1600×1200, but has shown improvements by enabling 32x anti-aliasing
Anti-aliasing
In digital signal processing, spatial anti-aliasing is the technique of minimizing the distortion artifacts known as aliasing when representing a high-resolution image at a lower resolution...
in SLI-AA mode, and support for 2560×1600 resolutions at much higher framerates than is possible with single or dual GPU systems with maximum settings in modern games. It was believed that high latencies severely marginalized the benefits of four GPUs, however much of the blame for poor performance scaling is due to Windows XP's API which only allows for a maximum storage of 3 extra frames. Windows Vista and Windows 7 are not limited in this fashion and shows promise for future multi-GPU configurations.
In March 2008, NVIDIA released the GeForce 9800 GX2 GPU. Targeted at high-end gaming, the 9800 GX2 is essentially two updated and slightly underclocked G92 8800GTS cores on a dual-PCB graphics card to compete with ATI's HD 3870×2. Though NVIDIA did not release Quad SLI drivers for the 9800 GX2 at time of release, the telltale SLI connector on the top of the card leaves little doubt that users in the future will be able to equip themselves with two 9800GX2s, thus allowing for a total of 4 GPUs in one system via only 2 PCI Express x16 graphics slots, a feat impossible since the 7950GX2. Note that NVIDIA no longer supports Quad SLI on Windows XP (NVIDIA will automatically prevent you from using two 9800GX2s without Windows Vista.)
Currently, the only GPUs that can support 4-way SLI are the GTX 480 and GTX 580, and they must be used on an Intel x58 or 5520 chipset combined with a Nvidia nForce 200 chipset, to provide extra PCI lanes.
3-Way SLI
NVIDIA has revealed a triple SLI setup for the nForce 700NForce 700
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...
series motherboards, which only works on Windows Vista. The X58 intel chipset also implement 3-way SLI using an additional NF200 component based on nForce 700
NForce 700
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...
. The setup can be achieved using three high-end video cards with two MIO ports and a specially wired connector (or three flexible connectors used in a specific arrangement).
The technology was officially announced in December 2007, shortly after the revised G92-based 8800GTS made its way out of the factory. In practical terms, it delivers up to a 2.8x performance increase over a single GPU system.
3-Way SLI is possible using all GeForce GTX except GTX 295 and GTX 460 (580, 570, 480, 470, 465, 285, 280, 275, 260). The GeForce GTX 295 does not support 3-way SLI but supports 4-way SLI and Multi-GPU. The 460 GTX was rumoured to support 3-Way SLI but upon release people found the 1 toothed 2-Way SLI bridge, this is because the 460 was not meant to replace the 260, it was supposed to push up the rest of NVIDIA's product line and make the 465 GTX more appealing, but due to heat issues 465 GTX's were considered flops and the mass of gamers stuck with 2-Way SLI 460 GTX.
Unlike traditional SLI, or CrossFireX
ATI CrossFire
AMD CrossFireX is a brand name for the multi-GPU solution 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.-First-generation:CrossFire was first made available to the public...
, 3-way SLI was limited to the GeForce
GeForce
GeForce is a brand of graphics processing units designed by Nvidia. , there have been eleven iterations of the design. The first GeForce products were discrete GPUs designed for use on add-on graphics boards, intended for the high-margin PC gaming market...
8800 GTX, 8800 Ultra, 9800 GTX and June 2008 introduced the GTX 260, GTX 280, the 9800 GTX+ and also the GTX 275, 285, 465, 470 and 480 graphic cards on the 680i, 780i 790i, certain P55 chipsets, X58 chipsets, whereas CrossFireX can be theoretically used on multiple ATI (now AMD) Radeon cards (up to 4-GPUSs, must have same core irrespective of product binning).
Quadro Plex
The NVIDIA Quadro PlexNVIDIA Quadro Plex
The Nvidia Quadro Plex is an external graphics processing unit designed for large-scale 3D visualizations. The system consists of a box containing a pair of high-end Nvidia Quadro graphics cards featuring a variety of external video connectors...
Visual Computing System is an external graphics processing unit
Graphics processing unit
A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...
designed for large-scale 3D
3D computer graphics
3D computer graphics are graphics that use a three-dimensional representation of geometric data that is stored in the computer for the purposes of performing calculations and rendering 2D images...
visualizations. The system consists of a box containing a pair of high-end NVIDIA
NVIDIA
Nvidia is an American global technology company based in Santa Clara, California. Nvidia is best known for its graphics processors . Nvidia and chief rival AMD Graphics Techonologies have dominated the high performance GPU market, pushing other manufacturers to smaller, niche roles...
graphics cards featuring a variety of external video connectors. A special PCI Express
PCI Express
PCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...
card is installed in the host computer, and the two are connected by VHDCI
VHDCI
The Very High Density Cable Interconnect is a 68-pin connector that was introduced in the SPI-3 document of SCSI-3. The VHDCI connector is a very small connector that allows placement of four wide SCSI connectors on the back of a single PCI card slot. Physically, it looks like a miniature...
cables.
The NVIDIA Quadro Plex system supports up to four GPU
Graphics processing unit
A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...
s per unit. It connects to the host PC via a small form factor PCI Express
PCI Express
PCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...
card connected to the host, and a 2 meter (6.5 foot) NVIDIA Quadro Plex Interconnect Cable. The system is housed in an external case that is approximately 9.5 inches high, 6 inches wide, and 20.6 inches in depth and weighs about 19 pounds. The system relies heavily on NVIDIA's SLI technology.
Physics calculation
In response to ATIAti
As a word, Ati may refer to:* Ati, a town in Chad* Ati, a Negrito ethnic group in the Philippines* Ati-Atihan Festival, an annual celebration held in the Philippines* Ati, a queen of the fabled Land of Punt in Africa...
offering a discrete physics calculation solution in a tri-GPU system, NVIDIA announced a partnership with physics middleware
Middleware
Middleware is computer software that connects software components or people and their applications. The software consists of a set of services that allows multiple processes running on one or more machines to interact...
company Havok
Havok (software)
Havok Physics is a physics engine developed by Irish company Havok. It is designed primarily for video games, and allows for real-time collision and dynamics of rigid bodies in three dimensions. It provides multiple types of dynamic constraints between rigid bodies , and has a highly optimized...
to incorporate a similar system using a similar approach. Although this would eventually become the Quantum Effects technology, many motherboard companies began producing boards with three PCI-Express x16 slots in anticipation of this implementation being used.
In February 2008, NVIDIA acquired physics hardware and software firm Ageia, with plans to increase the market penetration for PhysX beyond its fairly limited use in games; notably Unreal Engine 3. In July 2008, NVIDIA released a beta PhysX
PhysX
PhysX is a proprietary realtime physics engine middleware SDK developed by Ageia with the purchase of ETH Zurich spin-off NovodeX in 2004...
driver supporting GPU acceleration, followed by an official launch on August 12, 2008. This allows PhysX acceleration on the primary GPU, a different GPU, or on both GPUs in SLI.
In January 2009 Mirror's Edge
Mirror's Edge
Mirror's Edge is a single-player first person action-adventure video game developed by EA Digital Illusions CE and published by Electronic Arts. The game was announced on July 10, 2007, and was released for the PlayStation 3 and Xbox 360 in November 2008. A Microsoft Windows version was released...
became the first major PC game title to add NVIDIA PhysX to enhance visual effects in-game and add gameplay elements.
Hybrid SLI
Also in response to the PowerXpress technology from AMD, a configuration of similar concept named "Hybrid SLI" was announced on January 7, 2008. The setup consists of an IGP as well as a GPU on MXMMobile PCI Express Module
A Mobile PCI Express Module is an interconnect standard for GPUs in laptops using PCI Express created by MXM-SIG...
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.
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
GeForce 8 Series
The GeForce 8 Series, is the eighth generation of NVIDIA's GeForce line of graphics processing units. The third major GPU architecture developed at NVIDIA, the GeForce 8 represents the company's first unified shader architecture.-Naming:...
video card.
On November 5, 2008 in Microsoft’s Guidelines for Graphics in Windows 7 document, Microsoft stated that Windows 7 will not offer native support for hybrid graphics systems. Microsoft added the reason for the decision saying that hybrid graphics systems ‘can be unstable and provide a poor user experience,’ and that it would ‘strongly discourage system manufacturers from shipping such systems.’ Microsoft also added that ‘such systems require a reboot to switch between GPUs.’
On desktop systems, the motherboard chipsets nForce 720a, 730a, 750a SLI, 780a SLI and 980a SLI and the motherboard GPUs GeForce 8100, 8200, 8300 and 9300 support Hybrid SLI (GeForce Boost and HybridPower). The GPUs GeForce 8400 GS and 8500 GT support GeForce Boost, the GPUs 9800 GT, 9800 GTX, 9800 GTX+ 9800 GX2, GTX 260 and GTX 280 support HybridPower.
Nevertheless, the most common cards which can be purchased nowadays do not support HybridPower, as manufacturer of the cards do not place the necessary PIC16F690 on the Graphic-PCB. Although for all users the switching is possible with tray icon, only a handful cardtypes have the ability to switch off the power completely.
There is Kernel level support in Linux as of 2.6.34 However user tools to actually use the feature are fairly primitive at this time.
Caveats
- In an SLI configuration, cards can be of mixed manufacturers, card model names, BIOS revisions or clock speeds. However, they must be of the same GPU series (e.g. 8600, 8800) and GPU model name (e.g. GT, GTS, GTX). There are rare exceptions for "mixed SLI" configurations on some cards that only have a matching core codename (e.g. G70, G73, G80, etc.), but this is otherwise not possible, and only happens when two matched cards differ only very slightly, an example being a differing amount of video memory, stream processors, or clockspeed. In this case, the slower/lesser card becomes dominant, and the other card matches. Another exception is the GTS 250, which can SLI with the 9800 GTX+, as the GTS 250 GPU is a rebadged 9800 GTX+ GPU.
- In cases where two cards are not identical, the fastest card – or the card with more memory - will run at the speed of the slower card or disable its additional memory. (Note that while the FAQ still claims different memory size support, the support has been removed since revision 100.xx of NVIDIA's Forceware driver suite.)
- SLI doesn't always give a performance benefit – in some extreme cases, it can lower the frame rateFrame rateFrame rate is the frequency at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems...
due to the particulars of an application's coding. This is also true for ATI's CrossFire, as the problem is inherent in multi-GPU systems. This is often witnessed when running an application at low resolutions. - In order to use SLI, a motherboard with an nForce4NForce4The 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.-nForce4/nForce4-4x:...
, nForce 500NForce 500The nForce 500 is a motherboard chipset series and the successor to the nForce4 series. It was revealed by NVIDIA on 2006-03-07 and released on 2006-05-23...
, nForce 600NForce 600The 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....
or nForce 700NForce 700The 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...
SLI chipset must be used, although with the use of hacks one can make SLI work on motherboards with Intel, ATIAtiAs a word, Ati may refer to:* Ati, a town in Chad* Ati, a Negrito ethnic group in the Philippines* Ati-Atihan Festival, an annual celebration held in the Philippines* Ati, a queen of the fabled Land of Punt in Africa...
and ULiAcer Laboratories IncorporatedAcer Laboratories Incorporated is a major designer and manufacturer of integrated circuits for the personal computer and embedded systems markets. It is a subsidiary of the Acer group....
chipsets. NVIDIA has stated that only their own chipsets can allow SLI to function optimally, and that they will not allow SLI to work on any other vendor's chipsets. Some early SLI systems used Intel's E7525 XeonXeonThe Xeon is a brand of multiprocessing- or multi-socket-capable x86 microprocessors from Intel Corporation targeted at the non-consumer server, workstation and embedded system markets.-Overview:...
chipset, which caused problems when NVIDIA started locking out other vendor's chipsets as it limited them to an outdated driver set. In 2007, Intel has licensed NVIDIA's SLI technology for its SkullTrailIntel SkulltrailIntel's Skulltrail is an enthusiast gaming platform that was released on February 19, 2008. It is based on the company's 5400 "Seaburg" workstation chipset. The primary difference between Skulltrail and Intel's current and past enthusiast chipsets is a dual CPU socket design that allows two...
platform, and select motherboards supporting the Intel X58Intel X58The Intel X58 is an Intel chip designed to connect Intel processors with Intel QuickPath Interconnect interface to peripheral devices. Supported processors implement the Nehalem microarchitecture and therefore have an integrated memory controller , so the X58 does not have a memory interface...
(Tylersburg) chipset have unlocked SLI capabilities. Not all X58 motherboards support this technology, as NVIDIA offered it to motherboard manufacturers at the cost of $5 per motherboard sold. NOTE: As of the release of the AMD 900 chipset seriesAMD 900 chipset seriesThe AMD 9-Series Chipset is a set of chipsets developed by AMD, released in 2011. The chipset series uses the same silicon as AMD's previous 8-Series chipset however it's targeted at the socket AM3+ platform, including the Bulldozer line, while the 800 series is targeted at the socket AM3...
, SLI can be run on an AMD mainboard provided that it has the 970, 990X, or 990FX chipset on the board. - Vsync + Triple buffering is not supported in some cases in SLI AFR mode.
- Users having a Hybrid SLI setup must manually change modes between HybridPower and GeForce Boost, while automatically changing mode will not be available until future updates become available. Hybrid SLI currently supports only single link DVI at 1920×1200 screen resolution.
- When using SLI with AFRAlternate Frame RenderingAlternate Frame Rendering is a technique of graphics rendering in personal computers which combines the work output of two or more graphics processing units for a single monitor, in order to improve image quality, or to accelerate the rendering performance...
, the subjective framerate can often be lower than the framerate reported by benchmarking applications, and may even be poorer than the framerate of its single-GPU equivalent. This phenomenon is known as micro stutteringMicro stutteringMicro stuttering is a term used in computing to describe a quality defect inherent to multi-GPU configurations, such as nVidia SLi and AMD CrossFireX, using AFR...
and also applies to CrossFire since it's inherent to multi-GPU configurations.
See also
- Scan-Line InterleaveScan-Line InterleaveScan-Line Interleave from 3dfx is a method for linking two video cards or chips together to produce a single output. It is an application of parallel processing for computer graphics, meant to increase the processing power available for graphics. SLI from 3dfx was introduced in 1998 and used in...
by 3Dfx3dfx3dfx Interactive was a company that specialized in the manufacturing of 3D graphics processing units and, later, graphics cards. It was a pioneer in the field for several years in the late 1990s until 2000 when it underwent one of the most high-profile demises in the history of the PC industry... - ATI CrossFireATI CrossFireAMD CrossFireX is a brand name for the multi-GPU solution 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.-First-generation:CrossFire was first made available to the public...
– ATIATI TechnologiesATI Technologies Inc. was a semiconductor technology corporation based in Markham, Ontario, Canada, that specialized in the development of graphics processing units and chipsets. Founded in 1985 as Array Technologies Inc., the company was listed publicly in 1993 and was acquired by Advanced Micro...
's competing solution - MultiChromeMultiChromeMultiChrome is a technique by S3 Graphics to couple multiple graphics chips for better performance. It has first been used in the Chrome S20 series and later in Chrome 400 series graphics processors...
- Micro stutteringMicro stutteringMicro stuttering is a term used in computing to describe a quality defect inherent to multi-GPU configurations, such as nVidia SLi and AMD CrossFireX, using AFR...
External links
- NVIDIA's Official SLI Technology website
- NVIDIA's SLI Zone: SLI-optimized games
- NVIDIA's Windows Vista Capable GPUs
- Article "Multiple Graphics Card Technology" by Tim Smalley
- Article "NVIDIA's SLI: An Introduction" by Ryszard Sommefeldt
- Article "Dell's Quad SLI: A Story in Pictures" by Charlie Demerjian
- Article "NVIDIA SLI Support - Getting Better" by Brent Justice
- NVIDIA's Quad SLI: Demystifying the rumors by Brandon Bell
- Article "Quad SLI: GeForce 7900 GX2" by Tim Smalley
- Article "Quad SLI part deux: Build It Yourself" by Tim Smalley
- Article "NVIDIA and Havok bring SLI physics to life."
- Article "SLI vs. CrossFire" by Gabriel Torres
- NVIDIA SLI with CUDA
- GPU Comparison: NVIDIA vs AMD/ATI