First Look: AM2 DDR2 vs. 939 DDR Performance
by Wesley Fink on April 17, 2006 12:05 AM EST- Posted in
- CPUs
Socket 939 Fast DDR-400 vs. AM2 Fast DDR-2
DDR has a somewhat narrow operating range. Mainstream DDR might extend from DDR400 to perhaps DDR433. The very best, and most expensive, DDR might extend from DDR400 to a bit over DDR600. The useful range of fast DDR is even less because as the timings increase for higher speed the bandwidth starts to fall. Therefore top bandwidth with many of the top DDR products peaks somewhere in the DDR500 to DDR550 range and bandwidth normally drops as we move higher in frequency at poorer timings.
While ratios can be used with lower performing memory, the main purpose of ratios is to offset the performance limitations of cheaper memory so the user can enjoy the increased performance of overclocked processor without having to similarly invest in expensive memory capable of 1:1 memory overclocking. The point is that we will not be investigating memory ratios on DDR memory, since they are not generally used to increase memory bandwidth and performance.
DDR2 is a different animal when it comes to ratios. As DDR2 matured, memory makers and processor manufacturers have sanctioned higher and higher speed grades of DDR2 that are achieved with memory ratios. Users select and use higher rated DDR2 products to increase memory performance. On the Intel platform there was theoretically a price to pay since the memory controller was on the chipset.. This meant 1:1 DDR2 memory is theoretically top performance without compromise, while other speeds had some degrading from maximum performance due to the overhead of the FSB ratios.
AMD uses HyperTransport, which means there is no FSB. All memory speeds should theoretically perform as if they were 1:1 on HT. This simply means additional DDR2 speeds should carry no penalty at all. A user can choose DDR2-400, DDR2-533, DDR2-667, DDR2-800, DDR2-1066, and other DDR2 speeds based on performance needs and their budget, as there is no one speed which is best in a HyperTransport design.
For all of these reasons, performance of AM2 was benchmarked at DDR2-400, DDR2-533, DDR2-667, and DDR2-800. Due to limitations of current AM2 motherboards in that no timings faster than 3 are available for memory, all 4 speeds were evaluated at 3-3-3 memory timings. This is a fast memory timing for DDR2 at any of those speeds, as the fastest DDR timings we have tested at lower DDR2 speeds is 3-2-2. At DDR2-800, 3-3-3 are the fastest timings ever tested at this speed.
In addition, performance at DDR2-800 3-3-3, the fastest stock speed we could set on current AM2 boards with this memory, was compared to DDR performance at DDR400 2-2-2, which is generally the fastest stock speed on current Socket 939 motherboards. The performance difference is reported in %.
Benchmark results were very interesting. From a broad perspective, memory bandwidth and latency of DDR400 was matched by DDR2 at a speed of just over DDR2-533. Put another way, DDR2-533 provides equivalent bandwidth and latency to DDR400 on this 4th spin of AM2. DDR2-667 provided a bit better performance, and DDR2-800 3-3-3 provided a 12% improvement (lower number) in Latency over DDR400 and a 13.3% to 28.6% improvement in bandwidth depending on the memory benchmark used. It is interesting that memory writes enjoyed the biggest bandwidth boost.
Unfortunately, the added memory bandwidth did not translate into the kinds of increases in real-world gaming performance that many might expect. Gaming Performance at DDR2-800 3-3-3 at the same CPU speed increased 1% to 6.7% in our tests - with all except Call of Duty 2 in the 1% to 4% range. Call of Duty 1.2 was used in these tests, which supports dual processors, and test results did not follow the same expected scaling of other benchmarks. For this reason, the Call of Duty 2 results are considered suspect until we have more experience with Revision 1.2.
Since increased memory bandwidth did not translate into similar increases in gaming performance we can only conclude that this iteration of AM2 is not particularly memory starved - a result that was really expected. This does open the door for future upgrades and revisions of AM2 that might make better use of the available memory bandwidth with fast DDR2 memory.
DDR has a somewhat narrow operating range. Mainstream DDR might extend from DDR400 to perhaps DDR433. The very best, and most expensive, DDR might extend from DDR400 to a bit over DDR600. The useful range of fast DDR is even less because as the timings increase for higher speed the bandwidth starts to fall. Therefore top bandwidth with many of the top DDR products peaks somewhere in the DDR500 to DDR550 range and bandwidth normally drops as we move higher in frequency at poorer timings.
While ratios can be used with lower performing memory, the main purpose of ratios is to offset the performance limitations of cheaper memory so the user can enjoy the increased performance of overclocked processor without having to similarly invest in expensive memory capable of 1:1 memory overclocking. The point is that we will not be investigating memory ratios on DDR memory, since they are not generally used to increase memory bandwidth and performance.
DDR2 is a different animal when it comes to ratios. As DDR2 matured, memory makers and processor manufacturers have sanctioned higher and higher speed grades of DDR2 that are achieved with memory ratios. Users select and use higher rated DDR2 products to increase memory performance. On the Intel platform there was theoretically a price to pay since the memory controller was on the chipset.. This meant 1:1 DDR2 memory is theoretically top performance without compromise, while other speeds had some degrading from maximum performance due to the overhead of the FSB ratios.
AMD uses HyperTransport, which means there is no FSB. All memory speeds should theoretically perform as if they were 1:1 on HT. This simply means additional DDR2 speeds should carry no penalty at all. A user can choose DDR2-400, DDR2-533, DDR2-667, DDR2-800, DDR2-1066, and other DDR2 speeds based on performance needs and their budget, as there is no one speed which is best in a HyperTransport design.
For all of these reasons, performance of AM2 was benchmarked at DDR2-400, DDR2-533, DDR2-667, and DDR2-800. Due to limitations of current AM2 motherboards in that no timings faster than 3 are available for memory, all 4 speeds were evaluated at 3-3-3 memory timings. This is a fast memory timing for DDR2 at any of those speeds, as the fastest DDR timings we have tested at lower DDR2 speeds is 3-2-2. At DDR2-800, 3-3-3 are the fastest timings ever tested at this speed.
In addition, performance at DDR2-800 3-3-3, the fastest stock speed we could set on current AM2 boards with this memory, was compared to DDR performance at DDR400 2-2-2, which is generally the fastest stock speed on current Socket 939 motherboards. The performance difference is reported in %.
Benchmark results were very interesting. From a broad perspective, memory bandwidth and latency of DDR400 was matched by DDR2 at a speed of just over DDR2-533. Put another way, DDR2-533 provides equivalent bandwidth and latency to DDR400 on this 4th spin of AM2. DDR2-667 provided a bit better performance, and DDR2-800 3-3-3 provided a 12% improvement (lower number) in Latency over DDR400 and a 13.3% to 28.6% improvement in bandwidth depending on the memory benchmark used. It is interesting that memory writes enjoyed the biggest bandwidth boost.
Unfortunately, the added memory bandwidth did not translate into the kinds of increases in real-world gaming performance that many might expect. Gaming Performance at DDR2-800 3-3-3 at the same CPU speed increased 1% to 6.7% in our tests - with all except Call of Duty 2 in the 1% to 4% range. Call of Duty 1.2 was used in these tests, which supports dual processors, and test results did not follow the same expected scaling of other benchmarks. For this reason, the Call of Duty 2 results are considered suspect until we have more experience with Revision 1.2.
Since increased memory bandwidth did not translate into similar increases in gaming performance we can only conclude that this iteration of AM2 is not particularly memory starved - a result that was really expected. This does open the door for future upgrades and revisions of AM2 that might make better use of the available memory bandwidth with fast DDR2 memory.
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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?