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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0g1 - Wednesday, June 25, 2008 - link
In the article it says the GT200 doesn't need to do ILP. It only has 10 threads. Each of those threads needs ILP for each of the SP's. The problem with AMD's approach is each SP has 5 units and is aimed directly at processing x,y,z,w matrix style operations. Doing purely scalar operations on AMD's SP's would be only using 1 out of the 5 units. So, if you want to get the most out of AMD's shaders, you should be doing vector calculations.DerekWilson - Wednesday, June 25, 2008 - link
The GT200 doesn't worry with ILP at all.a single thread doesn't run width wise across all execution units. instead different threads execute the exact same single scalar op on their own unique bit of data (there is only one program counter per SM for a context). this is all TLP (thread level parallelism) and not ILP.
AMD's compiler can pack multiple scalar ops into a 5-wide VLIW operation.
on purely scalar code with many independent ops in a long program, AMD can fill all their units and get close to peak performance. explicit vector instructions are not necessary.
gigahertz20 - Wednesday, June 25, 2008 - link
http://www.hardwarecanucks.com/forum/hardware-canu...">http://www.hardwarecanucks.com/forum/ha...870-512m...The site above mounted an after market cooler on it and got awesome results. Either the Thermalright HR-03 GT is just that great of a GPU cooler, or the standard heatsink/fan on the 4870 is just that horrible. Going from 82C to 43C at load and 55C to 33C at idle, just from an after market cooler is crazy! I was hoping to see some overclocking scores after they mounted the Thermalright on it, but nope :(
Matt Campbell - Wednesday, June 25, 2008 - link
The HR-03GT really is that great. Check it out: http://www.anandtech.com/casecoolingpsus/showdoc.a...">http://www.anandtech.com/casecoolingpsus/showdoc.a...Our 8800GT went from 81 deg. C to 38 deg. C at load, 52 to 32 at idle. That's also with the quietest fan on the market at low speed. And FWIW, I played through all of The Witcher (about 60 hours) with the 8800GT passively cooled in a case with only 1 120mm fan.
-Matt
Clauzii - Wednesday, June 25, 2008 - link
I see no fan on that thing??! PASSIVE?? :O ??jeffreybt2 - Wednesday, June 25, 2008 - link
"Please note that this is with a single Zalman 92MM fan operating at 1600RPM along with Arctic Cooling MX-2 applied to the base."magnusr - Wednesday, June 25, 2008 - link
Does the audio part of the card support PAP? If not all blu-ray audio will be downsampled to 16/48...NullSubroutine - Wednesday, June 25, 2008 - link
I would just like to point out that the 4870 falls behind the 3870 X2 in Oblivion while in every other game it runs circles around it. To me it appears to be a driver problem with Oblivion rather than an indication of the hardware not doing well there. Unless of course the answer lies in the ring bus of the R680?orionmgomg - Wednesday, June 25, 2008 - link
I would love to see more benchmarks with the CPU OCed to at least 4.0All the CPUs you use can hit it NP.
Also, what about at least 2 GTX 280 Cards and their numbers. Noticed that you did have them in SLI cause the power comsumption comparisons had them, but you held back the performance numbers...
Lets see the top 4 cards from ATI and Nvidia compete in dule GPU (no punt intended)on an X48 with DDR3 1600 and a FSB of 400x10!
That would be really nice for the people hoe have performance systems, but may still be rocking out a pair of EVGA 8800Ultras, cause their waiting for real numbers and performance to come out - and their still paying off theye systems lol... :]
Ilmarin - Wednesday, June 25, 2008 - link
You're probably aware of these already, but I'll mention them just in case:* Page 10 (AA comparison) is malformed with no images
* Page 21 (Power, Heat and Noise) is missing the Heat and Noise stuff.
Heat is a big issue with these 4800 cards and their reference coolers, so it would be good to see it covered in detail. My 7800 GTX used to artifact and cause crashes when it hit 79 degrees, before I replaced it with an aftermarket cooler. Apparently the 4870 hits well over 90 degrees at load, and the 4850 isn't much better. Decent aftermarket coolers (HR-03 GT, DuOrb) aren't cheap... and if that's what it takes to prevent heat problems on these cards, some people might consider buying a slower card (like a 9800 GTX+) just because it has better cooling.
Anand, you guys should do a meltdown test... pit the 9800 GTX+ against the 4850, and the 4870 against the GTX 260, all with reference coolers, in a standard air-cooled system at a typical ambient temp. Forget timedemos/benchmarks... play an intensive game like Crysis for an hour or two, and see if you encounter glitches and crashes. If the 4800 cards can somehow remain artifact/crash free at those high temps, then I'd more seriously consider buying one. Heat damage over time may also be a concern, but is hard to test for.
Sure, DAAMIT's partners will eventually put non-reference coolers on some cards, but history tells us that the majority of the market in the first few months will be stock-cooled cards, so this has got be of concern to consumers... especially early adopters.