The Radeon HD 4850 & 4870: AMD Wins at $199 and $299
by Anand Lal Shimpi & Derek Wilson on June 25, 2008 12:00 AM EST- Posted in
- GPUs
Fixing AMD's Poor AA Performance
Now that we have a new architecture from AMD with improved AA performance, it's time again to look at a comparison of all the different AA modes these cards offer. No new modes have been introduced since the R600 and G80 reviews, but AMD has completely rebuilt their ROPs with special attention to hardware based AA resolve. In R600, hardware resolve wasn't much faster than shader based resolve, but this time around, AA runs blazingly fast whether its on the dedicated resolve hardware or on the shader hardware (since their is so much more shader hardware now even shader based resolve gets a giant boost).
The first thing we will want to look at are the MSAA modes. These are the modes we absolutely recommend for use with AMD hardware as all their other filters essentially low-pass filter the entire image by blending in neighboring subpixels. In any case, the results are very impressive for RV770.
The RV670 at 19x12 was limited in some way other than AA (it really couldn't keep up), but at 16x10 we can get a better idea of relative impact of AA. And clearly the RV770 quite improves fall off with increasing AA levels over the previous generation. One special thing to note is that the RV770 does fall off very gracefully to 8xAA. Since the RV670, G80 and GT200 all have sharp drops in performance when moving up from 4xAA to 8xAA, the RV770 really shines here. In fact, the few tests we did with 8xAA paints the 4870 in a much better light relative to the GTX 280. Remember from our earlier architecture discussion that Oblivion is the game where the GT200 had the largest performance advantage over RV770.
While 8xAA performance is all well and good, the image quality difference is just not enough for us to recommend enabling it over increasing resolution (or better yet, pixel density on LCD panels -- hello display makers). For those with panels that don't go over 1280x1024, it would be better to spend the extra money on a large panel than a $300 graphics card. The application where we see 8xAA making the most sense is on 50+ HDTVs used as computer monitors where the pixels are just plain huge. For the majority of desktop users though 4xAA is where it's at.
We did test the performance of all the other modes as well. NVIDIA's CSAA modes are quite good (they actually improve image quality rather than degrade it), but again, stay away from anything but AMD's "box" filtered AA.
The RV770 actually shows a bigger performance hit from enabling their tent filters than RV670. This is likely because the filters are run on shader hardware in both cases while RV770 has faster hardware resolve that can be used for normal AA resolve. If RV670 resolves "box" filtered AA on the shader as well this would explain the flatter performance in that case. Even more so than the image quality question, the fact that they perform lower really should be the nail in the coffin for AMD's tent filter garbage.
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DerekWilson - Wednesday, June 25, 2008 - link
it looks like the witcher hits an artificial 72fps barrier ... not sure why as we are running 60hz displays, but that's our best guess. vsync is disabled, so it is likely a software issue.JarredWalton - Wednesday, June 25, 2008 - link
Again, try faster CPUs to verify whether you are game limited or if there is a different bottleneck. The Witcher has a lot of stuff going on graphically that might limit frame rates to 70-75 FPS without a 4GHz Core 2 Duo/Quad chip.chizow - Wednesday, June 25, 2008 - link
It looks like there seems to be a lot of this going on in the high-end, with GT200, multi-GPU and even RV770 chips hitting FPS caps. In some titles, are you guys using Vsync? I saw Assassin's Creed was frame capped, is there a way to remove the cap like there is with UE3.0 games? It just seems like a lot of the results are very flat as you move across resolutions, even at higher resolutions like 16x10 and 19x12.Another thing I noticed was that multi-GPU seems to avoid some of this frame capping but the single-GPUs all still hit a wall around the same FPS.
Anyways, 4870 looks to be a great part, wondering if there will be a 1GB variant and if it will have any impact on performance.
DerekWilson - Wednesday, June 25, 2008 - link
the only test i know where the multi-gpu cards get past a frame limit is oblivion.we always run with vsync disabled in games.
we tend not to try forcing it off in the driver as interestingly that decrease performance in situations where it isn't needed.
we do force off where we can, but assassins creed is limiting the frame rate in absentia of vsync.
not sure about higher memory variants ... gddr5 is still pretty new, and density might not be high enough to hit that. The 4870 does have 16 memory chips on it for its 256-bit memory bus, so space might be an issue too ...
JarredWalton - Wednesday, June 25, 2008 - link
Um, Derek... http://www.anandtech.com/video/showdoc.aspx?i=3320...">I think you're CPU/platform limited in Assassin's Creed. You'll certainly need something faster than 3.2GHz to get much above 63FPS in my experience. Try overclocking to 4.0GHz and see what happens.weevil - Wednesday, June 25, 2008 - link
I didnt see the heat or noise benchmarks?gwynethgh - Wednesday, June 25, 2008 - link
No info from Anandtech on heat or noise. The info on the 4870 is most needed as most reviews indicate the 4850 with the single slot design/cooler runs very hot. Does the two slot design pay off in better cooling, is it quiet?DerekWilson - Wednesday, June 25, 2008 - link
a quick not really well controlled tests shows the 4850 and 4870 to be on par in terms of heat ... but i can't really go more into it right now.the thing is quiet under normal operation but it spins up to a fairly decent level at about 84 degrees. at full speed (which can be heard when the system powers up or under ungodly load and ambient heat conditions) it sounds insanely loud.
legoman666 - Wednesday, June 25, 2008 - link
I don't see the AA comparisons. There is no info on the heat or noise either.DerekWilson - Wednesday, June 25, 2008 - link
the aa comparison page had a problem with nested quotes in some cases in combination with some google ads on firefox (though it worked in safari ie and opera) ...this has been fixed ...
for heat and noise our commentary is up, but we don't have any quantitative data here ... we just had so much else to pack into the review that we didn't quite get testing done here.