First Look: AM2 DDR2 vs. 939 DDR Performance
by Wesley Fink on April 17, 2006 12:05 AM EST- Posted in
- CPUs
AM2 Overclocking vs. Socket 939 Overclocking
Comments are often made that any evaluation of AM2 should include overclocking. Those theorists argue that the faster processor clock will move AM2 to the higher "bus" speeds that make for better efficiencies of the DDR2 memory controller - or something along those lines. With the current state of pre-release motherboards and AM2 processors, it just isn't possible to design a test that runs the AM2 at the 666 processor clock as we would like - the hardware is just not there yet. However, we were able to overclock the CPU almost 40% and finally settled on a workable overclock of the AM2, 939, OCZ DDR2-1000, and Crucial Ballistix DDR500.
The DDR2 memory was perfectly stable at a 250x10 processor setting with a DDR2-667 strap. This results (5:3 ratio) in a DDR2-833 memory speed at 3-3-3-10 timings on an equivalent 2.5GHz x2 AM2 CPU. Similarly the Crucial Ballistix was able to run with stability at 250x10 on a downclocked FX60 x2. With 1:1 ratio this resulted in memory at DDR500 3-3-3-7 timings.
The DDR results are in the general ball park of overclocking that would yield the best bandwidth, as is the AM2 overclocking. Both test setups are running at speeds an Enthusiast might run on an overclock with air. We are thus comparing a fast DDR overclock to a fast DDR2 overclock, within each architecture's capability. We are also running the same memory timings, though the DDR2-800 is running at a faster, but typical, speed for DDR2 on the upcoming AM2 and Conroe processors.
The overclocked test results are very interesting. Comparing DDR500 3-3-3 to DDR2-833 3-3-3 reveals an even greater improvement in latency and bandwidth for the DDR2 than we saw comparing DDR2-800 3-3-3 to DDR400 2-2-2. This is really an unexpected result. DDR2-800 latency is now down to 43.2 and Everest bandwidth increases to 8.8GB/s. DDR2 bandwidth is now 8% to 29% better than the similarly overclocked DDR setup compared to a range of 6.5% to 28.6% on the stock testing. The biggest improvement in the overclocking is Reads, which increase 29% overclocked compared to a 13.3% improvement at stock.
You might expect with an even greater improvement in memory bandwidth, in particular READ speeds, and Latency that a similar improvement in gaming performance would occur. Unfortunately that does not happen, as gaming performance improvements are even less than our stock comparisons. Once again, higher memory bandwidth and lower latency of DDR2 on AM2 just do not translate into markedly improved gaming performance.
Hopefully, this last series of overclocked performance comparisons will finally put into perspective what is and is not possible with improved DDR2 memory performance. Clearly AM2 will launch a bit faster than current Socket 939 performance when comparing the same processor speed. However it is not likely that further increases in DDR2 bandwidth or latency will translate into further improvements in performance with the current AMD/Athlon64 architecture. Further improvements in AM2 performance will have to come with revisions to the core, more cores, die-shrinks and higher speeds, and increases in cache. The move to DDR2 will bring small improvements in performance, but DDR2 alone is not likely to bring the large performance boosts many hope for.
Comments are often made that any evaluation of AM2 should include overclocking. Those theorists argue that the faster processor clock will move AM2 to the higher "bus" speeds that make for better efficiencies of the DDR2 memory controller - or something along those lines. With the current state of pre-release motherboards and AM2 processors, it just isn't possible to design a test that runs the AM2 at the 666 processor clock as we would like - the hardware is just not there yet. However, we were able to overclock the CPU almost 40% and finally settled on a workable overclock of the AM2, 939, OCZ DDR2-1000, and Crucial Ballistix DDR500.
The DDR2 memory was perfectly stable at a 250x10 processor setting with a DDR2-667 strap. This results (5:3 ratio) in a DDR2-833 memory speed at 3-3-3-10 timings on an equivalent 2.5GHz x2 AM2 CPU. Similarly the Crucial Ballistix was able to run with stability at 250x10 on a downclocked FX60 x2. With 1:1 ratio this resulted in memory at DDR500 3-3-3-7 timings.
The DDR results are in the general ball park of overclocking that would yield the best bandwidth, as is the AM2 overclocking. Both test setups are running at speeds an Enthusiast might run on an overclock with air. We are thus comparing a fast DDR overclock to a fast DDR2 overclock, within each architecture's capability. We are also running the same memory timings, though the DDR2-800 is running at a faster, but typical, speed for DDR2 on the upcoming AM2 and Conroe processors.
The overclocked test results are very interesting. Comparing DDR500 3-3-3 to DDR2-833 3-3-3 reveals an even greater improvement in latency and bandwidth for the DDR2 than we saw comparing DDR2-800 3-3-3 to DDR400 2-2-2. This is really an unexpected result. DDR2-800 latency is now down to 43.2 and Everest bandwidth increases to 8.8GB/s. DDR2 bandwidth is now 8% to 29% better than the similarly overclocked DDR setup compared to a range of 6.5% to 28.6% on the stock testing. The biggest improvement in the overclocking is Reads, which increase 29% overclocked compared to a 13.3% improvement at stock.
You might expect with an even greater improvement in memory bandwidth, in particular READ speeds, and Latency that a similar improvement in gaming performance would occur. Unfortunately that does not happen, as gaming performance improvements are even less than our stock comparisons. Once again, higher memory bandwidth and lower latency of DDR2 on AM2 just do not translate into markedly improved gaming performance.
Hopefully, this last series of overclocked performance comparisons will finally put into perspective what is and is not possible with improved DDR2 memory performance. Clearly AM2 will launch a bit faster than current Socket 939 performance when comparing the same processor speed. However it is not likely that further increases in DDR2 bandwidth or latency will translate into further improvements in performance with the current AMD/Athlon64 architecture. Further improvements in AM2 performance will have to come with revisions to the core, more cores, die-shrinks and higher speeds, and increases in cache. The move to DDR2 will bring small improvements in performance, but DDR2 alone is not likely to bring the large performance boosts many hope for.
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peternelson - Saturday, April 15, 2006 - link
I notice all your tests were performed in 32 bit mode.
This cpu can handle 64 bit instructions.
While 64 bit registers (and more of them) allows faster data manipulations, that advantage is traditionally offset by the need for bigger wordsize of instructions.
So if the memory reading of the instructions is more memory-hungry that could be more use for this extra memory bandwidth.
Therefore I suspect IN 64 BIT MODE, there could be more advantage on a fast DDR2 than on a bandwidth-limited DDR system.
How to test this? Well you could run some 64 bit Windows and BENCHMARK FAR CRY in 64 bits version as it is available as 32 and 64 bit.
See if running in 64 bit with this new ddr2 memory negates the disadvantage of limited bandwidth for instruction feeding?
If so this would be increasingly an advantage in future as more people move to 64 bit OS, including at Vista-time.
smitty3268 - Saturday, April 15, 2006 - link
The larger instruction size is barely an issue. The real difference is that all pointers are doubles in size from 32 to 64 bits. This can lead to a significantly lower number of variables stored on the cache, which can lead to increased bandwidth usage.AnandThenMan - Saturday, April 15, 2006 - link
I agree with what you are saying. In 64 bit mode, that A64 *should* benefit from the increased DDR bandwidth.The problem is, the 64 bit version of Farcry was basically a scam and offered no performance or visual increases solely because it was a 64 bit optimized game. If I remember correctly, the extra visual effects in the 64 bit version were basicially enabled if run in 64 bit mode, but had little or nothing to do with actually being optimized for the A64 in 64 bit mode.
peternelson - Saturday, April 15, 2006 - link
I see your point too.
Yes some additional features could have been done on 32 bit version but were restricted to 64 bit platforms. But surely the compiled binary was actually a 64 bit binary even if not optimised much? In which case it would still be interesting to compare.
32 bit DDR versus 64 bit DDR and versus 32 bit DDR2 and versus 64 bit DDR2.
My hypothesis is that the speedup (even if small) from using the 64 bit binary over the 32 will be greater on AM2 DDR2 than the same test on 939 DDR.
I agree that Far Cry was not the best example, but you may know of other good benchmarks or games which are tuned for this.
eg the same four tests of PRIME95 (www.mersenneforum.org) which is available in 32 and 64 bit. The Trial factoring test benchmark shows a good speedup in 64 over 32 bit operations. But then that doesn't use main memory much as it is highly optimised to work inside the L1/L2 cache. There must be other suitable tests though to compare 32 and 64 bit on some memory intensive task with binaries optimised for each architecture.
IntelUser2000 - Saturday, April 15, 2006 - link
Right, the hypothesis for higher clock speed giving better increases were similar, however it gave less increases.
Wesley, there is another typo. On this page: http://www.anandtech.com/cpuchipsets/showdoc.aspx?...">http://www.anandtech.com/cpuchipsets/showdoc.aspx?...
DDR400 to DDR2-800 performance increase in CoD2 is said to be 10.6%. That is not correct. DDR400 to DDR2-533 is 10.6%, but DDR400 to DDR2-800 is only 6.7%. Check your calculation numbers please.
Wesley Fink - Saturday, April 15, 2006 - link
The calculation has been corrected. Thank you for catching this and bringing it to our attention.peternelson - Saturday, April 15, 2006 - link
You should not claim AMD's on-processor memory controller is UNIQUE".Unique means nobody else does it and it is a unique feature of AMD.
THAT is incorrect.
Although Intel don't do it, there are other chips that have on-chip DDR or DDR2 controllers including Clearspeed. I can even put a ddr or ddr2 controller (or several) into my own chip designs in a Xilinx FPGA because Xilinx license the design free for use in their chips.
Griswold - Saturday, April 15, 2006 - link
Pretty unique in the x86 world, isnt it?peternelson - Saturday, April 15, 2006 - link
No, actually it isn't. That was precisely my point.
Transmeta Efficeon and VIA C7 can both have on die memory controllers too.
They run x86 instructions quite happily.
Don't get me wrong, it's a good idea, it's just not UNIQUE any more.
Wesley Fink - Saturday, April 15, 2006 - link
Transmeta and the VIA C7 aren't really AM2 and Conroe competitors in most situations. However, I can conceive some applications where they might be. To be more precise I will try to use another word to describe the on-processor memory controller in the future.Do you work for VIA or Transmeta?