Multiple Graphics Cards

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Requirements for Dual Graphics Cards

To use dual graphics cards, your computer needs AMD or Nvidia technology that links the cards to produce a single output. The AMD graphics technology is CrossFire and the Nvidia technology is SLI. For each of these solutions, the computer must have a compatible motherboard and the motherboard must have the necessary PCI Express graphics slots.

To find out if the motherboard supports dual graphics cards, go to its official product page and check the specifications. Or, look for the Crossfire or SLI symbol on the box the motherboard came in.

Dual graphics cards also require a desktop case that is large enough to fit the extra hardware and a power supply that can run dual cards. The cards must be linked using a bridge connector; which may be included with either the GPU or the motherboard. Finally, the SLI or Crossfire feature must be enabled in the GPU driver control panel.

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SLI and Crossfire [ edit]

SLI (Nvidia) and Crossfire (AMD) is a feature where two graphic cards are linked together to become one virtual graphics card. When this happens only one graphic card can be connected to the monitor(s), the other card is just used for extra processing power. The idea behind this that the work will be split between the two graphic cards.

Using this feature requires that the driver have a good idea of what is going to happen every frame, so it knows how to schedule the work. This works well for video games since they perform the same render passes each frame (shader, main, post-process, for example). So each game has it’s own profile built into the driver for it’s particular usage pattern. This does not work well for TouchDesigner since every .toe will have a different usage pattern. Thus, there is no profile built into the drivers for TouchDesigner for SLI/Crossfire. We haven’t done much testing to see if there are any benefits to using SLI configurations with TouchDesigner. If you want to try, we suggest using the Alternate Frame Rendering method of SLI, as opposed to the Split Frame Rendering method. To see any speed improvements you would first need to ensure that your project is GPU bottle-necked. See the Optimize article for more information on determining bottlenecks.

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Before you install

Before installing a secondary video card, we recommend you review the below checklist first to help prevent possible issues in the future.

What to know before you go upgrading

Here are a few things to consider should you want to upgrade a system with a multi-GPU SLI or CrossFire setup. First off, you need a motherboard that has the necessary PCI Express x16 slots and that is also compatible with either or both technologies. You’ll also need a case that can physically accommodate and cool the graphics cards and a strong enough power supply to feed the cards with adequate power.

Not all PCI Express x16 slots are created equal. T
Not all PCI Express x16 slots are created equal. Two slots on this Intel motherboard look similar, but one features a full 16 lane electrical connection while the other has only eight.

The cards must also be linked together using a bridge connector, which is usually included with either the cards or the motherboard, and the SLI/Crossfire feature must enabled in your graphics driver control panel as well (we’ll show you how to do that in the next section).

SLI Mosaic and EyeFinity [ edit]

SLI Mosaic (Nvidia Quadro cards) and EyeFinity (AMD cards) binds multiple GPUs together to drive a large array of outputs. Using this you can output to many more monitors, which seem like a single large monitor to Windows.

Although multiple GPUs are used in this mode, the extra GPUs do not add performance to the system. In fact, using this mode will actually result in worse performance than an identical output canvas on a single GPU. This is because a single GPU is still doing all of the work, and the extra one(s) are just outputting the final image. The cost of synchronizing and moving images between the GPUs is extra overhead a single GPU configuration doesn’t have.

If a splitter such as a DataPath splitter can be used with a single GPU instead of multiple GPUs, that will perform better than using multiple GPUs.

Nvidia Specifics [ edit]

SLI Mosiac should not be confused with regular SLI, which involves connecting multiple cards for better single or dual screen performances.

You can see a table of supported SLI Mosaic configurations here. In particular take note that not all cards support ‘Seamless’ display, which means you will see tearing on your outputs. Also to get Premium SLI Mosaic (which is also needed for tear free output), you need one of the Nvidia certifed systems listed here.

A good more recent document on Mosaic Recommended Connections can be found here (Jan 2014).

Porting it about

Looking to the future, we’re hoping it will become even easier to give systems multi-monitor capabilities. It might have taken many years to shift the PC world from analogue VGA outputs to digital DVI – despite its limitations on resolution and single connection – but things are looking brighter.

DisplayPort and Thunderbolt can provide daisy-chained multi-monitor capabilities, along with interoperability between the two, Thunderbolt, DisplayPort and PCIe are all interrelated in a natural, evolutionary way.

PCI Express is an excellent high-speed serial bus, so it makes sense to use that as the basis for everything in the communication layer of the PC. DisplayPort does just that, extending PCIe to the display.

Thunderbolt takes this standard and extends it to all external devices. With 20Gbps throughput, it’s more than able to support two 2,560 x 1,600 displays at 60Hz. It will even have 4Gbps free, making future expansion easier than ever. Look out for it coming to a PC near you soon.

Who Should Run Dual Graphics Cards?

If you don't play video games or use two monitors with your computer, you won't see an improvement in system performance by running dual graphics cards. The cost of the motherboard, the cards, and the other core hardware can be expensive.

However, if you run games across several displays or at extreme resolutions, dual graphics cards will improve your game speed and enjoyment.

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