Catalyst 6.11 - Caught in the CrossFire

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Product(s): Crucial X1900XTXX1900GT
Provided By: Crucial
Price: ~$399USD, $219USD

Introduction:

On November 15, 2006 ATi released the Catalyst 6.11 drivers for their Radeon series of Graphics Cards.  This was primarily a bug-fix driver as the only major performance improvement was with Call of Duty 2 at high resolutions with Crossfire and 4xAA enabled.  Among the usual long list of bug fixes was the addition of Crossfire support for "any combination of Radeon® X1900 and X1950 installed in a system running either the Windows XP or Windows XP Professional x64 Edition operating system."  This intrigued us as we have a couple of X1900 graphics cards around the bench and have recently acquired an MSI 975X Platinum Motherboard which we recently reviewed over here.  Although we don't have matching cards, the release notes stated that we have the ability to mix and match X1900 and X1950 cards on the same system.  Thus begins out brief look at CrossFire performance when using an X1900XTX and an X1900GT in the same system.

In The CrossFire:

This article is not meant to be a be-all, end-all CrossFire analysis.  This is merely a quick look to see how software based CrossFire works (if it works) and what advantages there are to this setup.  Before we go any farther, let's take a look at the specs of the two cards we've got on the bench.

 

ATi X1900XTX & X1900GT Quick Specs
   
GPU
Core
Vertex Shader Engines
Textures / Clock
Pixel Shader Engines
Core Speed
MTexels / sec
Memory Speed
Memory Bandwidth
 







X1900 XTX
R580
8
16
48
650MHz
10400 MTexels/s
775MHz (1550DDR)
49.6GB/s









X1900 GT
R580
8
12
36
575MHz
6900 MTexels/s
600MHz (1200DDR)
38.4GB/s
                 
eVGA 7950GX2
G71
8 x 2
24 x 2
24 x 2
500MHz
24000 MTexels/s
600MHz (1200DDR)
76.8GB/s

 

As you can see above, the specs of the two cards don't exactly line up.  According to ATI, both cards will keep running at their stock speeds, but the X1900XTX will only run with 12 pipelines and therefore 36 shader engines like the X1900GT.  We'll cover a few more thoughts as we cover the Crossfire FAQ below.  We'll only cover a few of the popular questions below.  If you want to read the entire FAQ, head over here.

4. What is the difference between CrossFire Ready graphics cards and CrossFire Edition graphics cards?

  • CrossFire Edition graphics cards include a “compositing engine” chip on-board. This chip takes the partially rendered image from the CrossFire Ready graphics card, and merges it with the partially rendered image from the CrossFire Edition graphics card. The result is a complete frame rendered at up to twice the performance of a single graphics card.
  • Current high performance pairs require a CrossFire Edition graphics card and a compatible standard Radeon (CrossFire Ready) graphics card from the same series.
  • The new ATI Radeon X1950 PRO and X1650 XT cards use an internal CrossFire Interconnect.
  • Other configurations have two CrossFire Ready cards enabled by software.

6. What happens when you pair a 12-pipe CrossFire Edition card with a 16-pipe card?

  • In this scenario both cards will operate as 12-pipe cards while in CrossFire mode.

7. What happens when your CrossFire Edition card and and a compatible standard Radeon (CrossFire Ready) graphics card have different clock speeds?

  • Both cards will continue to operate at their individual clock speeds. Ideal performance is gained by properly matching cards.

13. How are the two graphics cards connected on a CrossFire system?

  • CrossFire Edition and compatible CrossFire ready cards are connected by an external cable. The cable is attached from the CrossFire ready card’s DVI connector to the CrossFire Edition high density input connector (DMS). The compositing engine combines the result of both cards to output a complete image.
  • Radeon X1950 Pro and X1650 XT cards use an all new, high-bandwidth internal CrossFire Interconnect for two way communication.
  • Certain CrossFire Ready cards do not require an external connector, just a compatible second card. CrossFire mode is then enabled via software and the cards communicate over the high speed PCI Express® bus on the motherboard.

On the next page we'll cover the test system, enabling CrossFire support and run some performance numbers.


Test Setup & Info:

Our test system includes mismatched cards as we previously mentioned.  Below is a list of the hardware and settings used for the article.

  • MSI 975X Platinum v.2 PowerUp Edition.
  • Intel Core 2 Quad QX6700 @ 3.2GHz
  • Crucial X1900XTX 512MB
  • ATI X1900GT 256MB
  • eVGA 7950GX2 1GB
  • 2GB Kit of Crucial PC2-8000
  • Seagate 7200.10 250GB HDD
  • Windows XP Pro SP2
  • Catalyst 6.11 Drivers
  • nForce 91.37 Drivers

Crossfire Setup
Crossfire Setup

As you can see above, we've got quite a mismatched setup, but according to the latest release notes this is supported by the Catalyst 6.11 drivers.  Both of these cards are "CrossFire Compatible" but are not CrossFire Master Cards.  Although the MSI 975X Platinum board is CrossFire ready, the actual Dual GPU rendering is accomplished purely by drivers over the PCIe bus.

Enabling CrossFire on this setup is very easy.  We jumped into the Catalyst Control Center, and selected the CrossFire section and simply clicked "Enable".  We received a message stating that because of the mismatched cards a reboot would be required.  I'm assuming this is to disable 12 of the Pixel Shader Engines on the X1900XTX.  After a quick reboot we were ready to rock.

Control Center & Device Manager
Control Center & Device Manager

 

For this basic look at Software Crossfire with the Catalyst 6.11 Drivers, we have only ran 3DMark benchmarks.  We ran 3DMark 2003, 2005 and the latest - 2006 and compared the results with a reference 7950GX2 graphics card.  Please keep in mind that the ATi CrossFire setup is limiting the X1900XTX to 36 Pixel Engines and therefore becomes a slightly overclocked X1900GT Crossfire setup.  According to ATi's FAQ, the X1900XTX will keep the same clock speed, but loses 25% of its Pixel Shader Engines.

3DMark Benchmarks

Conclusion:

I absolutely applaud ATi for their recent CrossFire enhancements.  A couple of months ago I was talking with a few other hardware analysts and we all agreed that CrossFire was a dead horse.  With the release of the X1950Pro and the X1650 series that include integrated CrossFire support, my hopes actually picked up somewhat.  Now with the release of the 6.11 Drivers and the ability to take a couple of regular X1900 or X1950 series cards and build a Dual GPU setup, I'm rethinking my dead horse statement.

Back in July of 2005, (yes, it's been that long) nVidia released their 77.76 drivers that allowed for "bridgeless SLI" with a couple of SLI capable cards.  I give kudos to ATi for finally catching the idea over a year later with their Catalyst 6.11 drivers and software CrossFire.  What ATi adds to the pot is the ability to link together a couple of different models, instead of two matching cards that are required for SLI.  I'm sure that an established hardware CrossFire link will give better performance that by pure software and the PCIe bus, but it's a start and a welcome addition to those of you stuck with a couple of non-Master CrossFire capable cards.  Bridgeless SLI suffers the same performance loss without the SLI bridge, but it offers much better performance that a single card as we demonstrated with our DIY SLI with DFI: Free Performance? Article back in September of last year.

Performance with Software CrossFire on non-matching cards is nothing to get too excited about as they are both required to run with the same number of pipes.  In the future we hope to get a couple of X1650 or X1950 Pro cards and explore CrossFire in greater detail as it looks like it may finally be a viable alternative to those wanting more GPU power than a single GPU can offer.

ATi is heading in the right direction and we look forward to better Dual GPU support from them in the future.  Now if the only had DX10 hardware and OpenGL support for Vista . . .