XMP Technology Implementation

We discovered certain peculiarities about the implementation of XMP (Extreme Memory Profile) technology on Asus P6T mainboard. If the board supports this technology, it allows loading all the settings automatically, including the higher voltages. As we already know from our article called Kingston HyperX DDR3-1866: 3GB Overclocker Memory Kit for Core i7 Platform, the modules SPD contain 1866MHz and 1800MHz respective frequencies. To activate XMP technology on Asus P6T mainboard, you have to change the “Ai Overclock Tuner” from “Auto” to “X.M.P.” and select the corresponding settings profile. By selecting the first profile the memory frequency is increased to 1867MHz, the memory voltage – to 1.66V, and “QPI/DRAM Core Voltage” – to 1.5V.

Gigabyte mainboards worked the same way, but we did find the differences when we selected the second profile, which has the memory working at 900MHz as DDR3-1800. Gigabyte mainboard lowers the processor clock frequency multiplier from x20 to x17, but increases the base frequency from 133MHz to 150MHz in this case. So, the resulting CPU frequency makes 2.55GHz, which is very close to the nominal 2.66GHz, and the memory works at 900MHz as DDR3-1800. The QPI bus voltage is increased to 1.45V. Asus P6T mainboard does exactly the same thing, but the CPU clock frequency multiplier is lowered not to x17, but only to x18. Asus’ approach seems to be more correct, because we don’t lose any of the CPU frequency, but even win a little bit, because it makes 2.7GHz instead of 2.66GHz. However, this frequency increase is so insignificant, that any CPU can work in this mode just fine.

However, 1.5V and even 1.45V voltage on the QPI bus seems to be a little too high. Gigabyte mainboards have it set at 1.175V by default, while Asus P6T has it at 1.2V. That is why we tried to do with a lower voltage setting without losing any operational stability. We succeeded with Gigabyte boards by raising the voltage only to 1.335V. Asus P6T, however, wouldn’t pass any stability tests until the voltage was set at 1.45V. The difference is not that dramatic in nominal mode, but during overclocking it mattered a lot, because increased “QPI/DRAM Core Voltage” pushed the CPU temperature up a lot.