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Memory Performance tuning – AM3+ / DDR3
PLEASE NOTE THAT THE AMD PRODUCT WARRANTY DOES NOT COVER DAMAGES CAUSED BY
RUNNING COMPONENTS OUTSIDE OF SPECIFICATION INCLUDING DAMAGES CAUSED BY
OVERCLOCKING (EVEN WHEN OVERCLOCKING IS ENABLED WITH THE AMD OVERDRIVE UTILITY).
Memory clock speed is tied to HT ref. clock with certain ratios. The following Memory clock modes are
available on the AMD “Scorpius” platform technology with AM3+ socket and DDR3 support:
• DDR3-800 (400MHz) – 2:1 ratio
• DDR3-1066 (533MHz) – 8:3 ratio
• DDR3-1333 (667MHz) – 10:3 ratio
• DDR2-1600 (800MHz) – 4:1 ratio
• DDR3-1866 (933MHz) – 14:3 ratio
• DDR3-2133 (1066MHz) – 16:3 ratio *
• DDR3-2400 (1200MHz) – 6:1 ratio *
(* = not an officially supported memory clock mode
In the case of AM3+ DDR3 platform and AMD FX-series CPUs there are two key strategies for Memory tuning:
1) utilize the maximum memory clock mode that matches your DIMM module specification (or known
performance tuning headroom) - example DDR3-1866 or DDR3-2133 mode with CL9-11-9 timings
2) utilize a lower memory clock mode with faster CL5-5-5…CL7-7-7 timings and HT ref. clock boost (the
amount of HT ref. clock boost will depend on the DIMM OC headroom) – example DDR3-1600 mode
with CL6-6-6 timings
Please refer to the DIMM module specification to determine the optimal Memory voltage value (example 1.65V).
The optimal Tras and Trc timing parameter value is calculated as follows:
Tras = Tcl + Trcd + Trp
Example: Tras should be set to 21 in case of CL7-7-7 -settings
Trc = Tras + Tcl
Example: Trc should be set to 28 in case of CL7 + Tras = 21 -settings
NOTE: Setting Trc to a higher value may improve the margins – example: 42
Enabling 2T –timing mode can improve stability with 4GB or 8GB memory configurations (but will cause a slight
performance hit).
The Memory controller of AMD Phenom and AMD Phenom II CPUs can be set to run in Ganged mode or in
Unganged mode. Ganged mode means that there is a single 128bit wide dual-channel DRAM Controller (DCT)
enabled. Unganged mode enables two 64bit wide DRAM Controllers (DCT0 and DCT1).
The recommended setting in most cases is the Unganged memory mode. Ganged mode may allow slightly
higher Memory performance tuning and performs well in single-threaded benchmarks.
Depending on the motherboard and BIOS, it may be required manually setting the timing parameters for each
DCT (in Unganged mode) when performance tuning the memory or fine tuning the timings. Some BIOS
versions apply the same timings automatically for both DCTs in an Unganged mode.
The DIMM slots furthest away from the CPU socket should be equipped first (usually marked as DIMM slot 1&3
or A2&B2).