Conroe vs. AM2: Memory & Performance

Core 2 Duo (Conroe) launched about twelve days ago with a lot of fanfare. With the largest boost in real performance the industry has seen in almost a decade it is easy to understand the big splash Core 2 Duo has made in a very short time. AnandTech delivered an in-depth analysis of CPU performance in Intel's Core 2 Extreme & Core 2 Duo: The Empire Strikes Back. With so much new and exciting information about Conroe's performance, it is easy to assume that since Core 2 Duo uses DDR2, just like NetBurst, then memory performance must therefore be very similar to the DDR2-based Intel NetBurst architecture.

Actually, nothing could be further from the truth. While the chipsets still include 975X and the new P965 and the CPU is still Socket T, the shorter pipes, 4 MB unified cache, intelligent look-ahead, and more work per clock cycle all contribute to Conroe exhibiting very different DDR2 memory behavior. It would be easy to say that Core 2 Duo is more like the AMD AM2, launched May 23^rd, which now supports DDR2 memory as well. That would be a stretch, however, since AM2 uses an efficient on-processor memory controller, and the launch review found Core 2 Duo faster at the same clock speed than the current AM2. This is another way of saying Conroe is capable of doing more work per cycle - something we had been saying for several years about Athlon64 compared to NetBurst,

The move by AMD from Socket 939 to Socket AM2 is pretty straightforward. The new AM2 processors will continue to be built using the same 90nm manufacturing process currently used for Athlon 64 processors until some time in early to mid-2007. AMD will then slowly roll-out their 65nm process from the bottom of the line to the top according to AMD road-maps. This could include memory controller enhancements and possibly more. Performance of AM2 only changed very slightly with the move to DDR2, generally in the range of 0% to 5%. The only substantive difference with AM2 is the move from DDR memory to official AMD DDR2 memory support.

Our AM2 launch reviews and the article First Look: AM2 DDR2 vs. 939 DDR Performance found that AM2 with DDR2-533 memory performed roughly the same as the older Socket 939 with fast DDR400 memory. Memory faster than DDR2-533, namely DDR2-667 and DDR2-800, brought slightly higher memory performance to AM2.

The Core 2 Duo introduction is quite different. Clock speed moved down and performance moved up. The top Core 2 Duo, the X6800, is almost 1GHz slower than the older top NetBurst chip and performs 35% to 45% faster. With the huge efficiency and performance increases comes different behavior with DDR2 memory.

With the world now united behind DDR2, it is time to take a closer look at how DDR2 behaves on both the new Intel Core 2 Duo and the AMD AM2 platforms. The performance of both new DDR2 platforms will also be compared to NetBurst DDR2 performance, since the DDR2 NetBurst Architecture has been around for a couple of years and is familiar. We specifically want to know the measured latency of each new platform, how they compare in memory bandwidth, and the scaling of both Core 2 Duo and AM2 as we increase memory speed to DDR2-1067 and beyond. With this information and tests of the same memory on each platform, we hope to be able to answer whether memory test results on Conroe, for instance, will tell us how the memory will perform on AM2.

In addition we have an apples-apples comparison of AM2 and Core 2 Duo running at 2.93GHz (11x266) using the same memory at the same timings and voltages with the same GPU, hard drive, and PSU. This allows a direct memory comparison at 2.93GHz at DDR2-1067. It also provides some very revealing performance results for Core 2 Duo and AM2 at the exact same speeds in the same configurations.