What do multiple graphics cards do?

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Overview [ edit]

Installing multiple graphics card in your computer can have benefits in some cases, depending on your situation. The most common case is adding support for more monitors, however you need to setup you system in a very specific was to get optimal performance.

See also Multiple Monitors, Sync In CHOP

Video

Can You Use Two GPU’s Without SLI or CrossFire?

Yes. It is possible to run two graphics cards without SLI. 

Just keep in mind that this kind of set-up is useful only in a very specific scenario — if you’re running multiple monitors. 

Sure, it is possible to run more than one monitor using a single graphics card. However, this will severely limit the performance of your graphics card if, let’s say, you’re running a GPU-intensive task, like rendering or playing video games. 

Running two graphics cards without using CrossFire or SLI is a good solution to this. 

By connecting each monitor to one graphics card, you’ll be able to effectively split the load between both graphics cards. This means that you can render videos or graphics on one monitor and then play a video game on the other. 

Some people do this to run multiple instances of the same game or software on one system and output it to separate monitors, as well as keyboard and mouse. 

Of course, it should go without saying that you need to have a system that supports such a setup. Your processor, in particular, should be able to handle such kinds of workloads if you plan on doing this. 

Now, if you don’t plan on doing this, then you’re just wasting your time and money trying to run a dual graphics card setup. 

If you already have an extra lying around though, it should make for a fun and neat experiment. 

GPU Affinity [ edit]

GPU affinity binds a single instance of TouchDesigner (one process) to a single GPU. With multiple GPUs in the system you can have multiple instances of TouchDesigner, each bound to a unique GPU. This avoids any GPU->GPU communication and puts multiple GPUs to work. One process could be using it’s 2 outputs to send data to projectors, while the 2nd GPU is connected to monitors you are using to run a 2nd TouchDesigner process that is controlling the show (sending commands and data streams to the first instance via the various networking OPs).

It is also a good solution if you are having Horizontal Tearing by avoiding connecting outputs with different resolution/refresh rate (EDIDs) to the same graphics card.

When using GPU Affinity, make sure that the windows from the TouchDesigner process which is bound to a particular GPU do not overlap onto the desktop space of the other GPU(s). If windows are shown on the wrong GPUs it will cause the data to get copied between GPUs which is what we are trying to avoid by using GPU affinity. This is acceptable for creating and editing your files, but during performance playback you should keep the windows only on monitors connected to the GPU that the process is bound to.

GPU Affinity is supported by Nvidia Quadro GPUs, and all modern AMD GPUs.

Affinity Usage [ edit]

GPU Affinity is used by using the -gpuformonitor command line option when launching TouchDesigner. This command binds the process to the GPU connected to the specified monitor. The monitors are indexed the same way they are in the Monitors DAT, which is left to right and bottom to top. You can specify any monitor that is connected to the particular GPU you want to bind to. For example if you only want run two instances of TouchDesigner, each running on the first and second graphic card respectively, and each GPU has only 1 monitor connected, you’d launch them with a .bat file like this:

To see if the binding is working as you expected, use the Monitors DAT and look at the ‘affinity’ column.

Geforce Cards [ edit]

GPU Affinity is not supported on Geforce level cards. It is not recommended that you use multiple Geforce cards in a single system. In Windows 7 or later all the work will get done by the fastest GPU and then final images will be copied to the other GPUs to be displayed on-screen. However the performance of this vs. Quadros is unknown. Even on Quadro’s working without GPU affinity is not a suggested way to work.

We can not offer support for graphics issues caused by using multiple Geforce cards in a single system.

Benefits

The primary benefit of running two graphics cards is increased video game performance. When two or more cards render the same 3D images, PC games run at higher frame rates and at higher resolutions with additional filters. This extra capacity improves the quality of the graphics in games. Most graphics cards render games up to 1080p resolution. With two graphics cards, games run at higher resolutions, such as on 4K displays that offer four times the resolution. In addition, several graphics cards can drive additional monitors.

A benefit of using an SLI or Crossfire-compatible motherboard is that a PC can be upgraded at a later time without replacing the graphics card. Add a second graphics card later to boost performance without removing the existing graphics card. Manufacturers upgrade graphics cards about every 18 months and a compatible card may be difficult to find after two years.

Setting up your own Crossfire and SLI systems

Assuming you have plenty of cooling, a compatible motherboard, and a power supply powerful enough to power the extra graphics cards, installing those cards in a system for SLI or CrossFire is relatively straightforward; the process isn’t much different than installing a single graphics card.

Begin by shutting down the system and unplugging it from the electrical outlet. Next, insert the graphics cards into the requisite PCI Express x16 slots on the motherboard and connect the necessary supplemental 6- or 8-pin power feeds for your particular cards. Then install the SLI or CrossFire bridge connector (or connectors) to link the cards together.

With the exception of a few low-end products, Nvidia GeForce and AMD Radeon graphics cards running in multi-GPU configurations require a bridge connector to link the cards together. For more than two graphics cards, you must use larger 3-way or 4-way bridges, or multiple single bridges.

Once everything is properly seated and secured, connect your monitor (or monitors) to the primary graphics card—typically the card in the PCI Express x16 slot closest to the processor on the motherboard. Then power up the system, let your operating system boot, and install the latest drivers for the graphics cards.

After you install the necessary hardware and drivers, you must enable CrossFire and SLI in your graphics control panel. You can find CrossFire settings in the “AMD CrossFireX” section (above) under Performance in the Catalyst Control Center, and SLI settings in the “Configure SLI, Surround, PhysX” section (below) of Nvidia’s GeForce drives.

After installing the graphics drivers, you may receive a notification that the system is SLI- or CrossFire-capable and be prompted to enable the feature. If not, simply open your graphics control by right-clicking on a blank section of your desktop and selecting either ‘Catalyst Control Center’ for AMD Radeon cards or ‘Nvidia Control Panel’ for GeForce cards from the menu, then navigate to the necessary menu to enable CrossFire or SLI. Find SLI-related settings can be found in the “Configure SLI, Surround, PhysX” section of Nvidia’s GeForce drives, and CrossFire settings in the “AMD CrossFireX” menu in the Performance section of the Catalyst Control Center.

So, When Do Multi-GPU Configurations Make Sense, Then?

The main reason why SLI and CrossFire exist it to help users get more performance in scenarios where even the most powerful single GPU setup won’t cut it.

So, nowadays, that means scenarios like trying to run games at max settings on a 1440P 144Hz (or higher) monitor with 144FPS. Or, trying to run games on a triple 4K monitor setup. Or, really any other extreme scenarios along those lines.

While graphics cards like the GTX 1080 Ti and GTX 1080 do perform well in 4K gaming and can handle most games on higher settings on a 1440P 144Hz monitor, the reality is that they still aren’t quite enough in some of those extreme use cases.

2-Way SLI scaling on the GTX 1080 shows significan
2-Way SLI scaling on the GTX 1080 shows significant performance increases on a 4K monitor.

And, that, really, is where multi-GPU configurations come into play. No, they won’t give double (at least, across the board), or triple, or quadruple the performance boost over running the same card on its own. However, if you’re looking to build a gaming computer so that you can play games on as high of settings possible, with as high of a framerate as possible (especially on a 4K or 1440P 144Hz monitor), then you’re probably working with a very high budget anyways. And, in that case, you can probably also afford to drop the extra money on a second (or third, or fourth) graphics card in order to squeeze out as much performance for those scenarios as possible.

The other instance where it makes sense to utilize a multi-GPU setup is when you have an older generation graphics card and it would offer you better price-to-performance to add a second card, rather than upgrading the old card to a higher-end single GPU.

For instance, if you have a GTX 970 and you’re looking to get more in-game performance out of your system, you might be better off picking up a second GTX 970 for about $175 (used) on eBay and that should give you a decent performance boost in the games that utilize SLI properly. On the flip side of that, you’d have to pay at least $400 currently in order to replace the GTX 970 with only a GTX 1070—which isn’t that significant of an upgrade when you consider that the GTX 970 is still a fairly new GPU.

Ultimately, if you are looking to build an extreme gaming computer so that you can push games at max settings with as high of a framerate as possible on higher resolution monitors with faster refresh rates, then going with multi-GPUs is an option you’ll want to consider.

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Is Two GPUs Worth It?

Not exactly. 

The thing is, we’ve only been able to finally utilize multicore processors properly. 

It took years, especially in video games, for developers to properly optimize titles to distribute work evenly across multiple cores. 

Why did we bring up processors in a discussion for graphics cards? It’s because a single graphics card alone can have dozens if not hundreds of cores.

This means that getting more than one graphics card to work together properly is a headache that most graphics cards manufacturers and developers would prefer not to deal with. 

Nvidia has already given up support for SLI as it is in a recent announcement

This effectively means that they’re passing on the responsibilities of implementing SLI support to the video game and software developers. 

Sure, as we’ve already mentioned, video game and software developers could take the time to optimize their games for multi-GPU support.

However, it’s an investment where only a minuscule percentage of gamers would benefit. This kind of effort just doesn’t make any sense for them. 

TLDR; skip the dual GPU set-up and buy the single fastest graphics card that you can afford.

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