SLI or CrossFireX

Is a Multiple Graphics Card Setup for Me?

The question: is SLI or CrossFireX?

Battle of the Brands:

In the graphic card world ATI or Nvidia also known as Radeon or GeForce, I am not a diehard fan of one or the other. I look for the the best deal available at the time I'm buying. Also, I tend to allow 2 generations between my upgrades. Mainly, I'm looking to get the best bang for my buck.

If video encoding is something you do alot of, Nvidia does support Cuda. If however, you're only interest is in gaming, both brands have perfectly acceptable cards at various price ranges.

Multiple Card:

The promise of multiple card solutions is:

• higher performance
• higher visual experience

Neither SLI or CrossFireX setups always give a performance benefit. Depending on the game's encoding, in extreme cases, frame rates can be lower. In those cases, low frame rate is tied to running at low resolutions.

On occasion when AFR (alternate frame rendering) is used, mirco stutter can occur regardless of whether SLI or CrossFireX configuration is in use.

However, keep in mind these negatives are the exception not the rule in having a multiple card solution.

Max number of GPUs per configuration:

ATI Radeon CrossFire:

• 2 GPUs

ATI Radeon CrossFire X (new version of CrossFire):

• Tri/3
• Quad/4

Nvidia GeForce SLI:

• 2 cards (up to 2 times the performance of a single GPU)
• Tri/3 (up to 2.8 times the performance of a single GPU)
• Quad/4

Hybrid:

A hybrid is when you can tap into the onboard graphics and your video card together. It doesn't matter if it's a SLI or a CrossFireX card both have hybrid solutions. Basically, you're taking 2 kinda slow video solutions, and making one not so slow one. The reason you would use a hybrid solution is if you have a low end video card.

It will not give a great performance boost to your intense 3d games. This is mainly a power savings option.

If you choose this solution, verify that your video card capable of it, before you purchase. Not all cards are. Beware, if you are playing intense 3d games, you will not enjoy this solution.

Motherboards:

Unless your motherboard documentation specifically says it supports a SLI or CrossFireX configuration, do not assume it can run either configuration. More of the newer motherboards (depending on chipsets!!) do give you the choice between running SLI or CrossFireX. However, you must verify that the motherboard will support the configuration you want. Depending on chipsets, a motherboard is either only a CFX or only a SLI. Do keep that in mind when picking your motherboard should you want more the one video card. Be sure to count the PCIe x16 slots too!!

Tips:

To get the most bang for your buck:

• 1 low end card in a hybrid configuration vs 1 mid range card = buy the mid range card
• 2 low end card vs 1 mid range card = buy the mid range card
• 2 mid range card vs 1 high end card = buy the high end card
• 2 high end cards vs 1 high end card = buy 2 high end cards

If you want to run multiple monitors, verify that the solution you've chosen can do it. Example: Driving multiple monitors in a ATI CrossFire solution is a bit tricky. Not that it cannot be done, but only under certain conditions.

What to know when pairing up graphics cards:

Graphics memory is not doubled. 2 cards with 1 GB each of graphics memory does NOT give you 2 GB of graphics memory. You still only have 1 GB of graphics memory.

Nvidia SLI cards need to be the same GPU category, they do not need to be the same manufacturer. If you mix a card with 1 GB of graphics memory with a card with 2 GB graphics memory they will operate at the graphics memory they have in common in this case 1 GB. In the newer cards both GPUs will operate at their default clock speed.

Nvidia SLI Cards:

• Matching GPUs
• 6 series or higher
• Use SLI connector
• PCIe x16
• Tri and Quad on newer motherboards
• Check motherboard support 16x16 is better then 16x8 which beats 8x8 over 4x4

ATI CrossfireX Cards:

• Do not have to match GPUs
  
• Must use CrossfireX connector
  
• Tri and Quadfire available with newer boards
  
• PCIe x16
• Check the motherboard support ie: 16x4/x8x8/4x4x4
• Card must be an X1550 or higher
  • X800/X850 are exceptions

On motherboard support keep in mind that there is a difference of 2~3% in FPS between 16x16 and 8x8. The lower the bandwidth used, does affect FPS. It's not a show stopper for me. Just an item to look at when I'm picking out my motherboard.

ATI CrossfireX has a compatibility chart worth checking out for pairing up options. However, I believe that it is best to purchase the exact same cards. Otherwise, the faster card is always waiting on the slower card. However, that may come down to you wanting to pair an existing card up with a new card.

Note:

In the multiple card solution I do not have a preference between SLI or CrossFireX. It truly depends on the fastest cards I can afford at the time of purchase. If I cannot get the ones I want at the price I am willing to pay, then I will purchase the best single card I can, rather then settling for less.

Be sure to research your options before you purchase. Be aware of bottlenecks. It's quite possible to bottleneck your gaming rig by not putting enough thought into your multiple card set up.

Return from SLI or CrossFireX to Video Card Basics

Video Card - Bit Rate or Memory Quantity, explanations on what affects speed.