Does AM2's Performance Make Sense?
Assuming for a moment that the performance we're seeing here today is representative of what AMD will show off in 2 months, does it make sense? AMD has effectively doubled their memory bandwidth but they've seen virtually no increase in performance, other than in some very isolated situations.
If you'll remember back to the introduction of AMD's Revision E core, we did an article about how the new core brought support four new memory dividers allowing you to run at speeds up to DDR500 without overclocking your CPU or the rest of your system. In that article we looked at the overall performance benefit of DDR-500 over DDR-400 on a Socket-939 platform in a variety of situations. A recap of our performance results is below:
| Benchmark | Socket-939 (DDR-400) | Socket-939 (DDR-480) | % Advantage (DDR-480) |
| Multimedia Winstone 2004 | 41.9 | 42.7 | 2% |
| 3dsmax 6 | 2.78 | 2.80 | 1% |
| DivX 6.0 | 50.6 fps | 53.2 fps | 5% |
| WME9 | 4.22 fps | 4.28 fps | 1% |
| Quake 3 (10x7) | 121.9 fps | 127.2 fps | 4% |
| ScienceMark 2.0 (Bandwidth)* | 5378 MB/s | 5851 MB/s | 9% |
As you can see, given almost a 9% increase in memory bandwidth, we saw similarly small increases in overall performance. It would seem that the Athlon 64, at its current clock speeds, just simply isn't starved enough for memory bandwidth to benefit from an increase in bandwidth. You'll also see that the areas where faster DDR memory helped back then are pretty much the areas where DDR2-800 is showing gains today.
Based on our results from back then, if a 9% increase in memory bandwidth doesn't increase performance tremendously, then the 35% increase in bandwidth we see with DDR2-800 on AM2 shouldn't yield any more of a performance increase. Or simply put, yes, our AM2 performance numbers make sense.
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savantu - Monday, April 10, 2006 - link
Anand , please correct the values in the table at the Adobe and multitasking tests , they should be negative.savantu - Monday, April 10, 2006 - link
..It's time so less is better.Anemone - Monday, April 10, 2006 - link
Don't forget capacity. If you loaded up 4 memory slots to bring 939 machines to 4gb, you harmed timings. DDR2 can bring 2gb on a module at good timings and thus make a higher performance 4gb machine. Why is this important? In Vista (yep I know it's delayed) you will find that gamers and power users of a wide variety will want 4gb machines, much the same as a good number of folks are starting to use 2gb machines now. The larger footprint of Vista ups the ante. It's not that 2gb won't be enough, it will do. Just as 1gb today "will do". But come the end of this year 4gb will start to be that cutting edge amount and that suits the use if DDR2 very well.You already mentioned the power issue, with 1.8V for DDR2. That is something AMD needed in the mobile arena to stay competitive, so if they were already designing a top notch DDR2 controller, might as well do the entire cpu line. Since much of the market is actually starting to shift to mobile solutions, from a growth standpoint, being competitive here is going to be telling in each company's numbers. Since Merom is having heat issues (hence why Conroe is coming out so far ahead of Merom, meaning less of a heat budget constraint) you can expect that Turion X2's with DDR2 will put some pain on Yonah machines. I suspect that AMD knows their bandwidth is superb with DDR2 and are designing Turion X2's with 512 cache because it doesn't hurt them much. Watch this area in 2006, because the world won't be painted blue if AMD does well here. Intel is likely well aware and will push as hard as possible to bring Merom out to keep AMD from making ground. Mobile designs under S1 socket are coming aplenty.
$.02
coldpower27 - Monday, April 10, 2006 - link
I must have missed it by what clock rate and what amount of cach were the models used???
Anand Lal Shimpi - Monday, April 10, 2006 - link
We purposefully didn't publish this information to protect our source of the CPU.Take care,
Anand
flyck - Monday, April 10, 2006 - link
well ofcourse we don't know the clock. But it is an important factor. @ 1.8GHz A64 didn't bennifit from dual channel. but it think @ 2.8GHz that story was totally different. So if you are testing @ 2.4GHz. there could be a larger gap @ 3GHz for example.Anand Lal Shimpi - Monday, April 10, 2006 - link
Very true, but from what I've seen the picture doesn't change much from the 3800+ up to the FX-62, at least with current CPUs/platforms. The main thing that shows a performance difference is when going to even lower latency memory. You are right though, the hungrier the CPU gets (faster clock, wider core, etc...) the more it depends on a high bandwidth memory bus. However, I do believe that AMD's own model numbers tell the tale of what to expect.I think that at the end of the day the 2 - 7% increase range is what will hold, with the vast majority of applications falling at the 2% end of the spectrum.
Take care,
Anand
ozzimark - Monday, April 10, 2006 - link
though one thing to keep in mind: memory efficiency is directly related to the cpu mhz. i've found that going from 2ghz to 3ghz while keeping the ram at 250mhz increases bandwidth by around 1800mb/s on my s939 rig :eek:Sunrise089 - Monday, April 10, 2006 - link
I think there will be a lot of current users taking the upgrade path in my subject line, or something close to it. I may very well buy a new AMD chip in 2007, I'd sure like to be able to, but for the next 12 months I only see myself buying a used, overclock proven 2x1meg cache s939 X2 at the end of summer, and then trading up to Conroe during the holidays. I can't really see anyone but the strongest fanboys (and I'm pretty strong) buying AM2.AnnonymousCoward - Monday, April 10, 2006 - link
Why in the world do you upgrade so often? My path might be AthlonXP 1800+ --> Conroe.