ATI's Multi-GPU Solution: CrossFire
by Anand Lal Shimpi & Derek Wilson on May 30, 2005 9:00 PM EST- Posted in
- GPUs
Super AA Modes
There are some older games that wouldn't see any benefit from a multi-GPU solution, as these titles may not be GPU limited. In order to provide some benefit to these games (while at the same time offering higher image quality), ATI has devised four multi-card display modes. These modes are user selectable from the control panel and can help add smoothness and clarity to any title.The compatibility of ATI's Super AA modes is not limited to any subset of titles because there is no workload split involved - each card renders the entire scene, each with a unique set of sample points. Before display, the compositing engine takes the output of each card and prepares a final image for display.
Two of the new modes simply make use of different sample points. 8xAA and 12xAA employ either 4x or 6x AA modes on each card. Of course, MSAA is limited in its ability to antialias certain aspects of a 3D scene. Multisample only works along polygon edges, while the slower supersample method works across the entire scene (including textures). SSAA has fallen out of use due to the rather large performance impact that it has on a single card. The modus operandi for SSAA is to render a scene at a higher resolution and then resample the image to the desired resolution. Of course, there are other ways of performing SSAA.
ATI is able to handle SSAA by rendering the entire scene at the desired resolution on each card with a half pixel diagonal shift. They combine this method with either their 8x or 12x MSAA modes in order to produce 10xAA (4x + 4x + 2xSS) and 14xAA (6x + 6x + 2xSS). These quality modes should prove to be phenomenal.
These 2xSS mode shouldn't be confused with a normal 2x vertical and 2x horizontal resolution mode. In that case, each pixel has 4 ordered sample points that scale down to one pixel. In ATI's mode, 2 sample points are used per pixel in a rotated grid fashion.
These modes add life to games that would not benefit otherwise from multiple graphics cards, as well as provide a compatibility mode to titles for which alternating or splitting frames is not an option. This is a key feature of ATI's CrossFire that separates it from NVIDIA, and we are very eager to get our hands on hardware and test it first hand.
Now that we know what ATI's CrossFire solution is and what it can do, let's take a look at how it stacks up to the competition.
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Calin - Tuesday, May 31, 2005 - link
"ATI should be focused on the overall platform, not necessarily building up support for their South Bridge. Although we do think it is a bit embarrassing to have to turn to another chipset vendor to provide working South Bridges for your motherboard partners. It would be one thing if this were ATI's first chipset, but it most definitely is not. "AMD first chipset (AMD 760 for Slot A Athlon, or Irongate, I think) had also non working USB support (or very buggy). Most mainboard manufacturers offered USB thru an add in PCI card, in order not to use the one included in the southbridge
Googer - Tuesday, May 31, 2005 - link
In theroy since It connets to the other card through DVI, I could use my old 9700pro in Crossfire mode with the newer card; even better is what if I could use an NVIDA card and ATI card in Crossfire! All I need is that moterhboard (if forgot the make and model) that supports PCI-e and Ture AGP! (not pci based agp)FakeName - Tuesday, May 31, 2005 - link
This is bogus, remember accelerator cards, mid-90's... poor solution then, same poor solution again... don't waste your hard earned money on this cerebral shortfall, the next gen will soon be upon us...Shinei - Tuesday, May 31, 2005 - link
Performance looks promising, sure, but I wonder what will be shown when AT gets hold of a sample for longer than a few benchmark runs--an 85% improvement at 1600x1200 seems a bit strange, particularly for hardware known for wheezing in the benchmarked game...CrystalBay - Tuesday, May 31, 2005 - link
Very sophisticated approach ATI...Hopefully the Composter doesn't turn to sh!t later on...sprockkets - Tuesday, May 31, 2005 - link
Hmmm, isn't the current SB on existing Radeon Express 200 boards buggy too?overclockingoodness - Tuesday, May 31, 2005 - link
#15: Regardless, what difference does it make? The performance would still be closer to what's presented in the article.overclockingoodness - Tuesday, May 31, 2005 - link
#15: You need to read more carefully. Notice how they said that it was the vendor's PC and not their own. So, obviously they had no choice. They had to go by whatever the vendor was offering at the time.flatblastard - Monday, May 30, 2005 - link
I was a little bummed after reading that the Crossfire + Xpress 200 would also have 2xPCI-e slots instead of just one like the current msi rs480m2-il. I was even more disappointed to here about the current state of the sb450. I thought the sb450 was supposed to fix the bugginess of sb400 which it is replacing? Oh well, no big suprise I guess considering their history in that department. So here's hoping for another save from uli.bob661 - Monday, May 30, 2005 - link
#16They weren't listed so I would imagine that they won't be compatible.