Both Nvidia's SLI and AMD's Crossfire allow you to combine/add a second, third or sometimes even a fourth similar generation graphics card (or add in more GPUs) to the one you already have in your PC. This way you effectively try to double, triple or even quadruple your raw rendering gaming performance (in theory). The reality is this though; the more GPUs, the worse the scaling becomes and the more driver issues you will run into. Honestly, two GPUs in most scenarios is ideal in terms of multi-GPU gaming, always remember that.
You could for example place two or more AMD graphics cards into a Crossfire compatible motherboard, or two or more Nvidia GeForce graphics cards in SLI mode on a compatible motherboard. In today's article we'll use two way SLI GeForce GTX 770 graphics cards.
A Crossfire compatible motherboard is pretty much ANY motherboard with multiple PCIe x16 slots that is not an nForce motherboard.
An SLI certified motherboard is an nForce motherboard with more than two PCIe x16 slots or a certified P55, P67, Z68, X58, Z77,Z87 or a X79 motherboard. Please check with the motherboard manufacturer whether or not it is SLI compatible. Keep that in mind, but most of the latest generations AMD and Intel based motherboards are compatible. A small note, if you are on an AMD processor then on AMD's side the 900 series chipset supports SLI as well.
Once we seat the similar graphics cards on the carefully selected motherboard, we just bridge them together with a supplied Crossfire connector or, in Nvidia's case, an SLI connector. Then install/update the drivers, after which most games can take advantage of the extra horsepower we just added into the system.
Screenshot of two cards with SLI enabled on the NVIDIA control panel.
Once you have your hardware setup it's time to install the latest drivers. In the Nvidia control panel, make sure that Maximize 3D Performance is activated. For SLI + Multi monitor setup you need to clock 'Span Displays with Surround'.
Multi GPU rendering -- the idea is not new at all. There are multiple ways to manage two cards rendering one frame; think of Super Tiling, it's a popular form of rendering. Alternate Frame Rendering, each card will render a frame (even/uneven) or Split Frame Rendering, simply one GPU renders the upper or the lower part of the frame. So you see, there are many methods where two or more GPUs can be utilized to bring you a substantial gain in performance.
The computer components used
To be able to understand what we are doing today, we need to briefly take you through some of the key components used for our PC. Today we have both a home built DIY (Do It Yourself) X79 based Core i7 system that consists of the following gear:
Core i7 3960X with all cores clocked at @ 4.6GHz
Motherboard -- MSI X79 Big Bang XPower II
Memory -- 8GB (4 x 2048 MB)
128 GB SSD for storage
1200 Watt Power Supply
Two GeForce GTX 770 graphics cards (reference speeds)
These are some pretty nifty parts and bear in mind, when you opt for multi-GPU gaming, always have your gear right. You'll need that quality power supply, you'll need that proper SLI supporting motherboard, a processor and then you'll need a chassis with some very decent airflow to keep the graphics cards nicely chilled down.The tests have been performed on a X79 / Core i7 3960X processor (six-cores) all overclocked to 4.6 GHz. There's no downclocking on long duration CPU load.
If you decide to go for high-end Multi-GPU gaming, our recommendation currently is an Core i7 processor based on a Z77/X79 motherboard as it has plenty of PCIe gen 2.0 and 3.0 lanes and thus cross-link bandwidth really is optimal. For installation, make sure you do not forget to use a proper SLI bridge -- your motherboard should come with them by default. If not, there is a wide variety available. As you can see with three dual slot cards, space is an increasing issue for airflow. Make sure you end up with a well ventilated PC chassis. Luckily the GeForce GTX 770 graphics cards have an exhaust located at the rear of the card.
You'll need a total of four PCIe PEG power connectors (2x 6-pin and 2x 8-pin) headed from your power supply. Purchase a good quality PSU preferably with high efficiency to save on power consumption. And with so much power under the hood, don't mess around with the Molex to PCIe 6/8-pin power converter cables okay? We'll show you a thing about power consumption on the next pages.
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