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DDR3 Memory: What Makes Performance Better?

AMD Setup

The AMD FX CPUs are rated by AMD to run up to 1866 DRAM at 1 DIMM per channel and up to 1600 with four DIMMs. This can be deceptive at both the upper and lower ends of their spectrum. I've seen and run a number of the upper-level CPUs with higher-frequency DRAM and seen many of the lower tier FXs that couldn't run the 1866 DRAM. This was one reason I chose 2400 DRAM as the test point. I fully expected to have to run the bulk of the testing at 2133, as I have seen very few FX CPUs that could handle 2400 DRAM, especially fully populated at 32GB. Pleased that I appear to have hit the lottery with my 8370, I believe that the Asus Crosshair V Formula Z may be another factor in the test system's exceptional stability. Higher priced than other AM3+ motherboards, I feel it's money well-spent.

Mixing Sets Of DRAM

Mixing sets of DRAM can be problematic, and this occurred with both the AMD Radeon DRAM and the ADATA sets. (Again, each sent two 2x8GB individual sets of DRAM, the first two 'sets' I tested with). Generally, the approaches taken to try and get mixed DRAM to play nicely can consist of timings and/or voltage adjustments. In the case of the AMD DRAM, it booted up fine and ran under the AMP settings until I tried to run Prime95, which promptly crashed. Raising the CPU/NB voltage (which runs the memory controller) by a slight + 0.06 increase stabilized the system. The ADATA sets didn't want to boot at all, but after a similar increase to the CPU/NB (+0.05), it booted and ran. Again, Prime95 was the nemesis, resulting in a crash. With this group of DIMMs, I raised the DRAM voltage to 1.7, and the CPU/NB another + 0.04, to achieve stability at 1.31. (Looking onward to the Intel build, I have little doubt that an actual four-stick packaged set of DRAM would have run without the additional adjustments.)

Without going into a bunch of boring details, I also tried mixing two sticks each from a variety of combinations of the DRAM available, with mixed results. I managed to get some to work together with voltage adjustments, two with timings adjustments, some with a combination of the two — and some combos just wouldn't work at all. In at least one case I tried with two Corsair sticks and two Team sticks, and they just wouldn't play at all — period! I then tried with the two remaining Corsair sticks and the same two Team sticks. That combination did play nicely. So it really goes to show that mixing DRAM is really a crapshoot; you never know if mixing sets/sticks of DRAM will play together.

Failure To Boot

Two of the sets wouldn't boot under DOCP at 2400 with all four sticks installed. I took another common tack with those sets and raised the CPU multiplier to 21.5 (raising the base frequency of the CPU from 4.0 to 4.3).  Additionally, when this slight OC was applied to the ADATA DRAM, it allowed the DRAM voltage to be lowered back to 1.65, though the CPU/NB voltage still had to be maintained at a lowered level of 1.26.

Failure Under Stress

There were three cases of this in Prime95, and all three were solved with slight CPU voltage increases. So, it wasn't really caused by DRAM faults.