AMD's CrossFireX: Tri & Quad GPU Preview
by Anand Lal Shimpi on February 21, 2008 3:00 AM EST- Posted in
- GPUs
The Test
| Test Setup | |
| CPU | AMD Phenom @ 2.6GHz |
| Motherboard | MSI K9A2 Platinum |
| Video Cards | ATI Radeon HD 3870 X2 ATI Radeon HD 3870 |
| Video Drivers | Catalyst 8.1 (Modified for CrossFireX Support) |
| Hard Drive | Seagate 7200.9 300GB 8MB 7200RPM |
| RAM | 2x1GB Corsair XMS2 DDR2-800 4-4-4-12 |
| Operating System | Windows Vista Ultimate 64-bit |
We ran the following games in their corresponding quality settings:
| Game | Resolution | AA | AF | Detail Settings |
| Half Life 2: Episode Two | 2560 x 1600 | 8X | 16X | Highest in-game |
| Unreal Tournament 3 | 2560 x 1600 | 0X | 16X | Highest in-game |
| Bioshock | 2560 x 1600 | 0X | 1X | Highest in-game |
| Call of Duty 4 | 2560 x 1600 | 4X | 16X | Highest in-game |
| Crysis | 1920 x 1200 | 0X | 1X |
High Quality defaults |
The graph below shows the performance levels you can get from a single GPU all the way up to four:
Obviously the biggest jump comes from one to two GPUs, but we still see some reasonable gains going from two to three. The value of a fourth GPU is simply nonexistent in most of the cases.
| Number of GPUs | HL2 | UT3 | Bioshock | CoD4 | Crysis |
| 1 x Radeon HD 3870 | 39.3 | 46.7 | 36.9 | 25.3 | 14.0 |
| 2 x Radeon HD 3870 (1 X2) | 71.9 | 84.1 | 63.2 | 50.0 | 26.2 |
| 3 x Radeon HD 3870 (2 X2 + 1) | 93.3 | 112.7 | 86.7 | 72.2 | 26.4 |
| 4 x Radeon HD 3870 (2 X2) | 102.2 | 114.6 | 92.5 | 93.2 | 27.7 |
Let's put some percentages with the graph above to put things into perspective:
| Configuration | HL2 | UT3 | Bioshock | CoD4 | Crysis |
| 2-way CF Improvement over 1 card | 83% | 80% | 71% | 98% | 87% |
| 3-way CF improvement over 2 cards | 30% | 34% | 37% | 44% | 0% |
| 4-way CF improvement over 3 cards | 10% | 3% | 7% | 29% | 4% |
| 4-way CF improvement over 1 card | 160% | 150% | 151% | 268% | 98% |
The move from one to two cards generally yields a healthy performance improvement, but the gains taper off as we look at the performance added by a third GPU. Call of Duty 4 is the only game that shows solid gains with 4 GPUs (29% over a 3-GPU configuration), the rest of the titles show mostly single-digit percentage improvements. Once again we see that Crysis simply needs new, faster GPU architectures - four GPUs does absolutely nothing for this game.
Remember our 3-way SLI review from earlier in the year? Although the test systems were very different, the GPU-bound scaling should be comparable (if anything, NVIDIA should have the advantage of being run on an Intel system). Here's a quick look back at some of the comparable benchmarks:
| Configuration | UT3 | CoD4 |
| 2-way SLI Improvement over 1 card | 84% | 90% |
| 3-way SLI improvement over 2 cards | 20% | 28% |
| 3-way SLI improvement over 1 card | 121% | 143% |
Single to dual GPU scaling is similar with SLI as CrossFire, but the 2-way to 3-way gain is better on CrossFireX. NVIDIA's quad-SLI is not yet available so we're not sure how the 4-way scaling will compare, but so far it seems like CrossFireX is doing quite well in the pure numbers game.
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PhantomKnight - Thursday, February 21, 2008 - link
Sorry getting used to the comment posting.This would have helped.
3 x Radeon HD 3870 (2 X2 + 1)
NicePants42 - Thursday, February 21, 2008 - link
I was also wondering what that meant. Looks like two 3870x2s plus one 3870.I was also a little confused about the system setup - looks like they were using nVidia hardware and drivers...
tynopik - Thursday, February 21, 2008 - link
obviously it's a typo and they meant 1 X2 + 1PhantomKnight - Thursday, February 21, 2008 - link
Am I alone in being confused, i thought that 2 times 2 plus 1 is equal to 5.Anonymous Freak - Thursday, February 21, 2008 - link
Previous 3870 CrossFire vs. 3870X2 reviews have shown that the X2 performs better than two standalone 3870s in CrossFire. So using "2 GPUs" as the X2 only might be deceptive. I want to see:One 3870
Two 3870s
Three 3870s
One 3870X2
One 3870X2 + one 3870
Two 3870X2s
(I don't think there is any board that could take four plain 3870s.)
Simply because from previous reviews, the "one to two" delta is much higher for X2 than for two plain 3870s. Another question is if the delta from one to two 3870s is the same as one to two 3870X2s. Based on previous X2 reviews, it looks like by all rights, the system really sees the X2 as a single double-fast GPU.
Goty - Thursday, February 21, 2008 - link
The MSI K9A2 Platinum can. =)Actually, I think that's the same motherboard used in this review.
Anonymous Freak - Tuesday, February 26, 2008 - link
Except when you use all four slots, they all drop to x8. And, yes, you would need a case with 8 back-panel slots, including one beyond the 'bottom' of the card. (Or you'd need to hack your cards to be single-slot.)strikeback03 - Friday, February 22, 2008 - link
How many cases have the openings on the back for 4 dual-slot cards?yyrkoon - Thursday, February 21, 2008 - link
"From AMD's explanation it sounds like there's still a lot of work to be done on the CrossFireX driver. While we can expect to see its public debut in March, it seems like it'll be a while before we're anywhere close to ideal scaling. We've found ourselves in this position with many-GPU designs in the past, at least the players are taking things a bit more seriously this time around."You guys, and many others have been talking about how well quad core CPUs scale(or dont) in a none server, are you really all that surprised to find that quad GPUs would be similar ?
I have been long suspecting that while the PCIe specification is absolute in how much bandwidth a number of PCIe lanes are supposed to have total, that motherboard manufacturers have been skimping as to how much they are allowing those lanes use. Maybe this is just now biting them in the behind ? Or maybe I am just being silly . . . ; ) Either way, system details are not exactly forthcoming here.
skiboysteve - Thursday, February 21, 2008 - link
... What?