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Friday, March 30, 2007
Other implementations of SLI - Wikipedia
Other Implementations
Two GPUs on one card
In February 2005, Gigabyte Technology released the GV-3D1-68GT, 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 only supported by one of Gigabyte's own motherboards, with which it was bundled.
Around March 2006, ASUS released the N7800GT Dual. Similar to Gigabyte's design, but mounting two 7800GT GPUs on one video card. Again, this faced several issues, such as high price (it retailed for around $800, while two 7800GT's were cheaper total at the time), limited release, and limited compatibility. It would only be supported on the nForce4 chipset and only a few 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 [1].
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 bolted 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.
A newer version, the GeForce 7950 GX2, addresses many issues in the 7900 GX2, and is available to consumers for separate purchase. More recently, in August 2006, NVIDIA has released the drivers to allow end-users to build their own quad-GPU systems using the 7950 GX2[1].
Quad SLI
In October 2005, Gigabyte Technology released the GA-8N SLI Quad Royal. Essentially it was a motherboard with four PCI-Express x16 slots. At the time of release however, NVIDIA stated that it would not be the direction it would take SLI [2].
In early 2006, NVIDIA revealed its plans for Quad SLI. Instead of combining two GPUs onto one board, two separate boards would be stacked on top of each other into one discrete unit, using the existing on-die SLI bridge connectors to send frame data. This way, four GPUs can contribute to performance.
The official implementations of Quad SLI work in the same fashion. Two GPUs are placed on two separate boards, 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 400MHz 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. One or both boards features an SLI connector, depending on the model.
Quad SLI has yet to show any massive improvements in gaming using the common resolutions of 1280x1024 and 1600x1200, but has showed improvements by enabling 32x anti-aliasing in SLI-AA mode, and support for 2560x1600 resolutions at smooth framerates (Typically 50FPS or better) on maximum settings.
NVIDIA has recently released official Quad SLI drivers, marking the first time one can use Quad SLI with official support.[3] For more information, visit NVIDIA's Quad SLI website.
Physics Calculation
In response to ATI 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.
Two GPUs on one card
In February 2005, Gigabyte Technology released the GV-3D1-68GT, 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 only supported by one of Gigabyte's own motherboards, with which it was bundled.
Around March 2006, ASUS released the N7800GT Dual. Similar to Gigabyte's design, but mounting two 7800GT GPUs on one video card. Again, this faced several issues, such as high price (it retailed for around $800, while two 7800GT's were cheaper total at the time), limited release, and limited compatibility. It would only be supported on the nForce4 chipset and only a few 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 [1].
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 bolted 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.
A newer version, the GeForce 7950 GX2, addresses many issues in the 7900 GX2, and is available to consumers for separate purchase. More recently, in August 2006, NVIDIA has released the drivers to allow end-users to build their own quad-GPU systems using the 7950 GX2[1].
Quad SLI
In October 2005, Gigabyte Technology released the GA-8N SLI Quad Royal. Essentially it was a motherboard with four PCI-Express x16 slots. At the time of release however, NVIDIA stated that it would not be the direction it would take SLI [2].
In early 2006, NVIDIA revealed its plans for Quad SLI. Instead of combining two GPUs onto one board, two separate boards would be stacked on top of each other into one discrete unit, using the existing on-die SLI bridge connectors to send frame data. This way, four GPUs can contribute to performance.
The official implementations of Quad SLI work in the same fashion. Two GPUs are placed on two separate boards, 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 400MHz 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. One or both boards features an SLI connector, depending on the model.
Quad SLI has yet to show any massive improvements in gaming using the common resolutions of 1280x1024 and 1600x1200, but has showed improvements by enabling 32x anti-aliasing in SLI-AA mode, and support for 2560x1600 resolutions at smooth framerates (Typically 50FPS or better) on maximum settings.
NVIDIA has recently released official Quad SLI drivers, marking the first time one can use Quad SLI with official support.[3] For more information, visit NVIDIA's Quad SLI website.
Physics Calculation
In response to ATI 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.
Definition of SLI - Wikipedia
Scalable Link Interface (SLI) is a brand name for a multi-GPU solution developed by NVIDIA for linking two (or more) video cards 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. With SLI, it is possible to theoretically double the power of your graphics solution just by adding a second identical video card.
The name SLI was first used by 3dfx under the full name Scan-Line Interleave, which was introduced in 1998 and used in the Voodoo2 line of graphics accelerators. When 3dfx collapsed financially, its intellectual property was purchased by NVIDIA. NVIDIA later reintroduced the SLI name in 2004 and intends 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
The basic idea of SLI is to allow two (or more) graphics processing unit (or GPU) to share the work load when rendering a 3D scene. Ideally, two identical cards are installed in a motherboard that contains two PCI-Express x16 slots setup in a master-slave configuration. Both cards are given the same scene to render, but effectively half of the work load is sent to the slave card through a connector dubbed the SLI bridge. The slave then sends its rendered output to the master card, where it is incorporated into the master card's frame buffer and sent to the screen. In its early implementations, motherboards capable of SLI required a special card, which came with the motherboard, that fit into a socket, usually located between the first and third PCI-Express slots. Depending on which way the card was inserted, the motherboard would allow the full x16 lanes for a single GPU configuration available. If it was in SLI mode, the motherboard would split the 16 PCI-Express lanes in both slots to only allow a maximum of 8 lanes per card. Motherboards today do not require this card due to advances in their chipsets and drivers. Also due to the advancement in available bandwidth, most modern SLI-capable motherboards allow each video card to use all 16 lanes in the PCI-Express x16 slot instead of having a split.
The SLI bridge used to reduce bandwidth constraints. 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 the new 80.XX drivers from NVIDIA. Since lower end to mid-range graphics cards have lower data transfers, data can be relayed through just the chipsets on the motherboard. This is also possible on ATI CrossFire. Both CrossFire and SLI suffer severe performance penalties when this method is used on two high end cards as the bus will be loaded down with data both from the CPU as well as the slave sending data to the master.
SLI offers two rendering and one anti-aliasing method for splitting the work between the video cards:
The rendering first method, known as Split Frame Rendering (SFR), 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 work as well as the other rendering method, however.
The rendering second method is known as Alternate Frame Rendering (AFR), in which one GPU processes even frames, and the second processes odd frames, one after the other. When the secondary card finishes work on a frame (or part of a frame) the results are sent via the SLI bridge to the master GPU, which then outputs the completed frame. 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 1.9 x the performance of one card, with the dual-card setup. However, this mode cannot be used in games that use Render To Texture functions, as neither GPU can directly access the frame buffer of the other. (There is another mode, AFR2, which can be manually chosen, but NVIDIA has not documented the difference between it and normal AFR.)
The anti-aliasing method is 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, and the second GPU uses a pattern offset by an equal amount in the opposite direction. Compositing both the results gives higher image quality than is normally possible. This mode is not intended for higher framerates, 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 and SLI 16X. A Quad SLI system is capable of SLI 32X 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
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