Geek 101: Should I Buy A Second Graphics Card?

If you’re looking to kick your PC’s graphical performance up a notch, the simplest solution is to upgrade your graphics card. But sometimes shelling out some cash for a better GPU simply isn't an option. What if you can't afford a top-of-the-line card? Or, in a more perfect world, what if you already own a high-end graphics card, but you still want better performance? In some cases, it's smarter (and cheaper) to buy a second card rather than swap out your current GPU for a better model.

This week we took a look at some of the graphics cards we have on hand down in the lab and ran them through some pretty rigorous performance tests to determine whether it's smarter to double down or trade up.

This liquid-cooled Maingear Shift sports three Nvidia GeForce GTX 580 cards.

Why Buy Two Graphics Cards?

Today we’re talking about multi-GPU solutions that allow your PC to split the graphical workload between two or more cards at the same time, which means more frames per second for you.

There are caveats. Consider power consumption: if you plan to run multiple graphics cards, you'll need a power supply that's up to the task. You'll also need to make sure there are free PCI-Express slots on your motherboard (and space inside your chassis) to pack in an extra graphics card.

You also can't combine cards from different product lines: your AMD Radeon HD 6970 won't play well with an Nvidia Geforce GTX 580, and you might even have trouble pairing the 6970 with another Radeon card from a different series (like the AMD Radeon HD 6870). For best results, make sure you use two identical cards when setting up a dual-GPU PC.

For example, if your current PC packs an Nvidia GeForce GTX 560 Ti and you're looking to upgrade, you could shell out $500 for the more powerful Nvidia GeForce GTX 580. Or, you could spend $250 for a second 560 Ti and run the two matching cards in SLI mode.

SLI (Scalable Link Interface) is Nvidia's proprietary method of parallel graphical processing. It allows two graphic cards to share the work of rendering an image.To figure out which configuration was faster, we tested them both in the PCWorld Lab on the Maingear Shift Super Stock, on Codemasters' Dirt 2, and Ubisoft's Far Cry 2. Click on the graph below to see a larger version of our results.

Check out our detailed test results!

According to our lab tests running Far Cry 2 at 2560-by-1600 screen resolution on high graphic settings, the two pair of GTX 560 Ti cards running in SLI will spit out more frames per second than a solitary GTX 580 at the same resolution (113 vs. 77, respectively.)

Running off-road rally racer Dirt 2 on the same test machine gave us similar results: with two GeForce 560 Ti cards running in SLI mode and all graphic settings turned to high we managed to eke out 115 frames per second while playing at 2560-by-1600 resolution, while running the same demo with a single GTX 580 card barely gave us 84 frames per second. In short, there was a noticeable performance improvement using two cheaper graphics cards instead of a single, more expensive card. The total cost of the two GPU setups is the same (2 x $250 vs. 1 x $500), but if you're upgrading from a single card it's much cheaper to simply double down, and you'll get better performance to boot.

Our lab tests suggest you can score a similar performance increase with Radeon cards by delaying your upgrade in favor of doubling up your current card. While upgrading the GPU in our test machine from an AMD Radeon HD 5870 to an AMD Radeon HD 6970 nearly doubled our framerate running Far Cry 2, we observed an even greater improvement slotting in a second 5870 card and running the two identical cards in tandem using CrossFire. CrossFire is AMD's proprietary parallel processing technology for graphical renderers that (just like Nvidia's SLI tech) allows two cards to share the work of one.

Do you need more than one graphics card? Absolutely not. But if you're looking for better performance and you want to save some money, using multiple cards at once via SLI or CrossFire will afford you better performance than simply swapping out your solitary card for a better version. There's one more angle to consider: keeping your upgrade path open. If you're buying a new PC (or building one yourself) and have room in your budget, getting a pricier card up front will give you room to maneuver later on, whether you're adding more PCI-dependant hardware, or foresee picking up an identical high-end card later on.

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