Mini-review: the effect of memory speed on AMD Trinity APUs

Does faster memory have any effect on the performance of the CPU?


Faster memory = faster integrated graphics performance?

When we test RAM modules we tend to say that the speed of the RAM has no significant impact on the performance of Intel systems. Intel's smart cache and memory controller make it so the CPU almost always retrieves the necessary data from the memory beforehand. No matter if its DDR3-1333, DDR3-1600 or DDR3-1866 RAM, we've never seen more than a 5 percent difference in performance aside from the specific memory benchmarks. In games and other standard software you don't notice any difference.

And while this is true for Intel processors, it's not necessarily the case for AMD chips, more specifically APUs with integrated graphics. With these processors the memory bus is shared between the CPU and GPU cores, which means the memory is under more load. AMD also hasn't developed prefetching algorithms and other things that can mask the speed of the RAM to the extent Intel has. 

In order to find out exactly what the influence of RAM speed is on AMD processors, we put an AMD A10 5800K processor on an ASUS F2A85-V Pro motherboard and ran a number of benchmarks at various memory speeds. We used Kingston HyperX Beast DDR3-2400 CL11 modules that are able to run at all speeds. The results are:

AMD A10 5800KDDR3-1333DDR3-1600DDR3-18661866 vs 1333
3DMark 11 Performance 1375 1506 1536 11,7%
3DMark - Fire Strike 827 936 974 17,8%
Tomb Raider - Low - 1920x1080 30,5 fps 35,5 fps 36,7 fps 20,3%
Hitman Absolution - Low - 1920x1080 18,7 fps 22,0 fps 24,0 fps 28,5%
BioShock Infinite - Low - 1920x1080 22,2 fps 26,0 fps 27,7 fps 24,8%
Dirt Showdown - Low 1920x1080 50,7 fps 62,6 fps 63,2 fps 24,6%
Cinebench 11.5 3,29 3,27 3,27 -0,6%
Cyberlink Espresso 14:30 14:08 13:55 4,2%
Cyberlink Espresso met acc. 10:29 10:20 10:18 1,8%
TechArp x264 Benchmark Pass 1 71,0 fps 71,4 fps 73,1 fps 3,0%
TechArp x264 Benchmark Pass 2 20,7 fps 20,8 fps 20,9 fps 1,2%

The performance differences for 3D benchmarks and games, which really tax the integrated GPU, are significant. In 3DMark 11, DDR3-1866 offers almost a 12% increase in performance. In 3DMark Fire Strike it's almost 18%. In games it's even more, more than 20% in Tomb Raider, almost 25% in BioShock and Dirt and almost 30% in Hitman Absolution. 

Those significant differences are limited to games, however. In CPU benchmarks like Cinebench and the TechArp x264 video encoding test it's negligible. In CyberLink Media Show Espresso, where we convert an hour of HD video, it was no more than a 4% difference. When we enable GPU accelleration, the relative performance gain decreased.

One thing is clear. If you have an AMD system and use integrated graphics, it's definitely worth investing in fast RAM. An increase of up to 30 percent is huge, and it can mean the difference between a game being playable and not playable.

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