AM2 Memory Performance

The move by AMD from the current Socket 939 to Socket AM2 is pretty straightforward. We know the new AM2 processors will continue to be built using the same 90nm manufacturing process currently used for Athlon 64 processors; AMD does not show roadmaps with AM2 processors built on 65nm until early 2007. To this point AMD has also reiterated that AM2 will not bring any changes to the Athlon 64 core. In other words, the socket will change to the new AM2 Socket 940, but under the hood the current 939 and the upcoming AM2 940 will beat with the same heart. The only substantive difference expected with AM2 is the move from DDR memory to official AMD DDR2 Memory support.

With that in mind it is time to delve more deeply into the what is really new in AM2 - support for DDR2 memory with AMD's unique on-processor memory controller. Many have expressed expectations of remarkable performance increases for DDR2 on AM2. This would be at odds with what we have seen from DDR2 in the past. With the move of Intel's NetBurst architecture to DDR2 there were really no gains at all in memory performance. Those expecting big gains point out that the AM2 on-chip memory controller, like the Athlon 64 on-chip DDR controller, should provide much lower latency and higher efficiency than Intel's chipset-based memory controller for DDR2.

This is our first opportunity to look more closely at an AM2 DDR2 controller that might answer these questions about memory performance, since it is the first AM2 design to outperform Socket 939. Earlier AM2 spins could not match 939 memory performance, but they continued to improve. This is remarkable when you consider that new Intel processors pretty much have performed like final shipping processors some 5 months ahead of launch. AMD, on the other hand, has done most of their development work on the DDR2 memory controller in the last 3 months with just 6 weeks remaining before launch.

The most recent AM2 roadmap is still showing AM2 launching June 6, 2006 at Computex in Taipei. With just 6 weeks to go before launch, there is not a lot of time for surprises with AM2. As pointed out in AMD Socket-AM2 Performance Preview, there is not much wiggle room when OEMs expect mid-May shipments of AM2. All of this leads us to believe that our fourth spin of AM2 this year is very close to what will actually be shipping on June 6th. We can always hope for surprises, but given what AMD has said so far we should be very close to final silicon.

You already know that the AM2 does modestly outperform Athlon64 Socket 939. What will be explored here is how the memory controllers compare in latency and bandwidth, memory performance at various DDR2 settings compared to fast DDR400 2-2-2 memory, and basic overclocking performance of AM2 compared to Socket 939 when the CPU and memory are both pushed to improve performance.

Memory Test Configuration
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  • Ecmaster76 - Saturday, April 15, 2006 - link

    Wouldn't it be the best way to suck up bandwidth? We already knew a single core had enough bandwidth from the 754-939 transition.

    I guess its not that big a deal now because the parts aren't even for sale. But as long as you do tsome multitasking articles on the final hardware I'll be happy.
    Reply
  • IntelUser2000 - Saturday, April 15, 2006 - link

    So... the conclusion is that DDR2-800 is needed to outperform DDR400. DDR2-667 is slower than DDR400. The Inquirer is correct, contrary to some other opinions. Reply
  • Wesley Fink - Saturday, April 15, 2006 - link

    Latency and Bandwidth of DDR2-533 are about the same as DDR400, and DDR2-667 and DDR2-800 are both faster. Games and Applications SHOULD be faster on both DDR2-667 and DDR2-800. However, given current aopplications and the AM2 memory controller, the applications and games are about the same at DDR2-667 - and DDR2-800 is faster as you state.

    This is likely the result of the late pre-release AM2 memory controller and applications/games themselves not being optimized for DDR2 on AM2. Both will likely be fixed very quickly, and actual performance of DDR2-533 should then be roughly on par with DDR400 - with 667 and 800 both faster.
    Reply
  • psychobriggsy - Saturday, April 15, 2006 - link

    If 2.5GHz was a 40% overclock, then the AM2 processor tested must have been running at 1.8GHz (9x200, i.e., it was also unlocked for you to get 10x250).

    It's not surprising that a 1.8GHz K8 processor wouldn't benefit from DDR2 much - indeed I expect that most of the application improvements were just from the slightly reduced latency at DDR2-800 rather than actually having more bandwidth available.

    I wonder what a stock 2.8GHz AM2 X2 with DDR2-800 would get against a stock 2.8GHz 939 X2 with DDR-400? No, I don't think it will be a miracle, but just possibly it will start actually needing the extra bandwidth available, which could lead to a greater gap between the two platforms.

    I guess we'll find out in under 2 months.
    Reply
  • Wesley Fink - Saturday, April 15, 2006 - link

    The AM2 processor was NOT a 1.8GHz x2. I stated the CPU could overclock 40% at stock speeds, but the 10x250 is not that 40% overclcok. We chose that ratio because it is a clock speed our DDR2 memory could handle and it was also a speed doable on 939 for a reasonable comparison. We actually had two AM2 processors this round, a top-line AM2 and a more mainstream processor. We looked at performance from both, and it was the same at the same processor speed. The DDR2 memory controller reports as Rev. F.

    As for the question about manufacture date, we are providing as little information about these pre-release processors and motherboards as possible to protect our sources. We have several sources who work with us to bring you the latest news before anyone else, and we don't want to compromise those relationships. Therefore we are not providing any information that might make it easier for AMD and others to trace our sources.

    We can assure you these are the latest Rev. AM2 shipped to AMD partners in early April as we have evaluated 4 versions since mid-January. This is also the first rev. to fully support DDR2-800.
    Reply
  • Viditor - Saturday, April 15, 2006 - link

    quote:

    we are providing as little information about these pre-release processors and motherboards as possible to protect our sources

    Fair enough...had to ask.
    Reply
  • Viditor - Saturday, April 15, 2006 - link

    My concern is that while Anand is just receiving the part, if it's off of a recent production run then AMD will have some problems with the launch. Usually you need a full turn's worth of product in inventory for a launch...if they are just turning out final product now, then my guess is there will be shortages come July. Of course since they have doubled their capacity recently it will be much less, but still...it doesn't bode well.

    Anand, could you confirm the manufacture date of the chip you tested for us please?
    Reply
  • Viditor - Saturday, April 15, 2006 - link

    Apologies...I should have addressed the previous question to Wesley (sorry mate).
    I know that APM allows AMD to change anything (even down to individual dice on the wafer) at any point in the process, but my concern is inventory levels here. If you could please confirm the production date on the chip you used for testing, it would help me significantly with my analysis of the upcoming launch.

    Cheers!
    Reply
  • Jynx980 - Saturday, April 15, 2006 - link

    Typo on page 3, paragraph 5:
    quote:

    we DDR timings we have tested
    Reply
  • Wesley Fink - Saturday, April 15, 2006 - link

    The extra "we" has been removed. Reply

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