At first glance, the AI Tweaker menu looks extremely complicated, probably the most complicated overclocking menu I’ve seen that wasn’t on a DFI board. It’s really not as bad as it looks, once you separate the important settings from the tweaks.
Overclocking opportunities begin with the “AI Overclock Tuner”, as with most Asus boards. The choices are a little different here than on LGA 775 boards, options are “Manual”, “Auto”, “D.O.C.P.”, and “XMP” if you happen to be using XMP capable memory.
“Manual” is the simple way to overclock, and really isn’t different from the Core 2.raise the BCLK (Base Clock Frequency), and you automatically raise the QPI, which is somewhat the equivalent of FSB on the LGA 775. CPU speed is a function of BCLK x “CPU Ratio”, which is the same thing as the traditional “Multiplier”.
DOCP (DRAM Overclock Profile) and XMP are both overclock functions used to set memory clock. Memory clock on the P6T series is a function of the BCLK, raising the memory clock necessarily raises the BCLK. Both settings use the memory’s SPD to automatically determine timings and VDIMM.
The P6T will run memory up to DDR3-2000.but wait, it isn’t so simple. Asus advertises that memory speeds of DDR3-1600 as OC, which is very true, the CPU must be overclocked to get those speeds. Attaining higher memory speeds requires raising the BCLK to high levels and lowering the CPU Ratio or lowering BCLK and increasing the CPU Ratio much like trying to get high FSB on LGA 775. The problem here is that the i7 920 and 940 are both locked at CPU Ratio of 20x, so you are limited to raising BCLK and lowering the CPU Ratio. Also involved is the QPI, which is 4.8GT/s on these two processors.this is the bandwidth for the memory and data bus, and appears to limit how high the BCLK can be raised regardless of CPU Ratio. The i7 Extreme 965 has a QPI of 6.4GT/s, and unlocked CPU Ratio. Much more experimentation on my part needs to be done, but at this point in time I am not able to clock my memory much over DDR3-1700. So it seems that DDR3-2000 probably can only be attained with the 965.
Now that I have thoroughly confused you (and myself), let me simplify it all. It seems at this time the consensus is that since the triple-channel gives you so much more memory bandwidth than dual-channel, and since memory has gotten so cheap, don’t worry that you can’t get your memory clocked that high. Tightening the timings gets you more performance than higher memory clock anyway, so even if you can’t afford the grand that the Extreme 965 costs, you can get the DDR3-1866 or DDR3-2000 memory, run the memory around DDR3-1333, crank down the timings, overclock your processor, and you’ll be very happy.
Basic overclocking is fairly simple. Set the AI Overclock Tuner to “Manual. Disable “Intel SpeedStep Tech”, which also disables Intel Turbo Boost, an “on the fly” overclocking feature of the i7, explained in the i7 920 review. You don’t want Turbo Boost causing your overclock to fail by further overclocking.
Overclock by raising the BCLK. If I’m not mistaken, the P6T is the first Asus motherboard I’ve had that doesn’t display your realtime CPU frequency on the overclocking menu. I really miss it here, get out the pen and paper to determine your clock speed.
There are a lot of voltage tweaks, the primary ones are “CPU Voltage”, “QPI/DRAM Core Voltage”, and “DRAM Bus Voltage”. QPI/DRAM Voltage is a little confusing, it should be called “UNCore Voltage”. “DRAM Bus Voltage” is the VDIMM. These should be within 10% of each other, and neither should be over 1.65v.though the closest setting to 1.65 on the P5T is 1.66. Triple-channel memory will generally run at 1.65, so going higher than that will only be needed when overclocking triple-channel, or using memory designed for dual-channel. Asus and Intel highly discourage using memory that must run at voltages over 1.65v. When overclocking, I would also enable “Load-Line Calibration”.
The P6T BIOS is missing a setting that the Gigabyte board I tested has, the UNCore Multiplier. The UNCore should be running at twice the Memory Frequency. I assume that it is taken care of automatically.
After a lot of experimentation, the most stable overclock I got was 3.88gHz. The system booted easily at 4.0gHz, but was a little unstable so I dropped it down just over .10gHz, where it was rock solid. This is a 50% overclock!