Catalyst 6.11 - Caught in the CrossFire

Product(s): Crucial X1900XTX, X1900GT
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.

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.