Memory performance

Since Athlon 64 motherboards rely on the processor's on-die memory controller, any differences in our memory subsystem tests are a result of how each mobo manufacturer has chosen to tune the on-die controller. As you can see, the Expert's tuning is definitely more aggressive than its competitors. Not even DFI's own RDX200 can match its memory bandwidth or latency.

Exploring the Expert's memory controller configuration with A64 Tweaker reveals that while timings are pretty tight overall, the idle cycle limit deviates quite a bit from the norm. The idle cycle limit refers to the number of clock cycles that a memory page can remain open without being accessed. Longer cycle time limits tend to favor streaming applications, and shorter limits yield better performance with more random access patterns. Most motherboards set the idle cycle limit around 16 clocks, but the Expert is set to a much higher 256 clocks.

While the Expert's longer idle cycle time and tighter overall timings yield faster memory performance than the competition, the more aggressive memory controller tuning isn't recommended for all memory modules. We tried several pairs of DIMMs with the board, and while low latency modules like Corsair's XMS Pro and OCZ's Platinum Rev 2 had no problems with the aggressive tuning, a pair of OCZ's Value Series DDR400 sticks consistently produced errors in Prime95. Not even the BIOS's optimized defaults were relaxed enough for the budget memory modules, and the board doesn't provide fail-safe defaults with more conservative timings.

In the end, we were able to get the Expert stable and error-free with our budget DIMMs by manually backing off memory timings in the BIOS. DFI has apparently elected to sacrifice broader compatibility in favor of faster performance with low latency modules, and for a high-end overclocking board like the Expert, that makes a certain amount of sense. We elected to continue testing with the board's aggressive defaults because the Corsair XMS modules we used to test all our systems were perfectly content with the tighter timings.