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Overclocking

I have to admit that theoretically it would be too optimistic to expect a significant performance boost from the transition to DDR3 SDRAM. As we know, the bandwidth of dual-channel DDR2-800 SDRAM is 20% higher than the front side bus bandwidth of the top Core 2 Duo processors, and the bandwidth of DDR2-1066 – 60% higher. That is why the memory is evidently not the bottleneck of contemporary systems, even if the CPU supports 1333MHz bus.

However, we shouldn’t forget that the bus in some systems works at much higher frequency than the default 1333MHz. These are overclocker platforms, where the bus frequency increase is the major tool for efficient processor overclocking. Maybe these are the systems where the new memory with higher bandwidth can really show its best? To answer this question we decided to perform some additional tests of the high-speed DDR3 SDRAM kits in an overclocker platform.

For this test session we took Core 2 Duo processor overclocked to 3.8GHz. New CPUs on G0 core stepping can easily hit this frequency. Although we selected a CPU with 9x clock frequency multiplier for our tests, 3.8GHz frequency was set as 8x475MHz in order to achieve higher bus bandwidth. To ensure that the CPU was running stably we raised its Vcore to 1.5V.

Overclocking like that in a system equipped with DDR2 SDRAM leaves the user two alternatives: you can either clock the memory synchronously at 950MHz, or use 5:6 or 4:5 divider and get the system memory to work at 1140MHz or 1188MHz. We decided to check out both cases and tests the system with DDR2-950 and 4-4-4-12 timings and as DDR2-1188 with 5-5-5-15 timings.

The next divider – 2:3 – gives us 1425MHz on the memory bus, which is unattainable for the existing DDR2 SDRAM. However, overclocker DDR3 SDRAM, such as Kingston HyperX KHX11000D3LLK2/2G and OCZ DDR3 PC3-10666 Platinum Dual Channel, can work just fine at this speed. We used this opportunity for our performance comparison between DDR2 and DDR3-1425 SDRAM with 6-7-6-18 timings.

This is the best you can get from currently available DDR3 SDRAM. The nest divider of 5:8 requires the memory to work at 1520MHz, however, the existing modules on Elpida chips cannot do that even with the least aggressive timing settings available.

So, let’s start with synthetic benchmarks as usual.

Unfortunately, DDR3 overclocking doesn’t change the overall tendency that we have already seen in the previous test session. DDR3-1425 shows higher bandwidth than DDR2-950, but lower than DDR2-1188. When it comes to latencies, the situation gets even worse: overclocker DDR2 SDRAM leaves DDR3 absolutely no chances.

 
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