Asus ROG Crosshair IV Formula
Our overclocking procedure is fairly simple but effective. The first task is to find the motherboard's Maximum Stable Base Frequency. With a maximum base frequency determined, we then try multiple combinations of CPU HTT and CPU Multiplier to find a "sweetspot" processor frequency. Other factors kept in consideration are the Memory Frequencies and the CPU's Northbridge Frequency.
The return of the dreaded Vdroop?
For those who aren't aware, Vdroop is a sudden drop in supplied Voltage to the CPU when a load is applied. It's been some time since I've written about this however it seemed quite apparent that the Crosshair IV Formula seems to suffer from this. The phenomena was observed with both initial release and the later 0602 BIOS. Given the board's power regulation spec, we were a little surprised to see a VDroop this substantial.
The board does indeed come with Asus' Load Line Calibration feature which completely eliminates the problem. It does remain a little perplexing as to why the VDroop is so bad without LLC and why it wasn't enabled by default. I concede that the LLC feature may occasionally cause instability under certain overclocked configurations but that doesn't explain why anyone would voluntarily prefer to feed their processor a high voltage under idle and a drooped voltage under load from out of the box.
We fully appreciate that a large proportion of AMD's Processor line-up are Black Edition processors and therefore have upwards unlocked CPU Multipliers. For many, the Base Hypertransport parameter will be nigh on redundant. Regardless, a motherboard of this calibre must offer the flexibility to use such a fundamental variable to it's maximum ability. Initially our journey was cut short at a maximum bootable frequency of 291MHz. However, with the release of a more recent BIOS (version 0602) this was expedited to a much healthier 330MHz. For those who are too cool for unlocked CPU Multipliers, you're most certainly in luck here.
Maximum CPU Frequency
As always it took some time to find the ideal combination of Frequencies and Voltages but we finally got there. At this point, I would like to say that the Asus Crosshair IV BIOS is a pleasure to work with and regardless of the amount of abuse it received, it always recovered. After applying the new 0602 BIOS, we were able to achieve a final CPU Frequency of 3913MHz, accompanied by a 313MHz base clock, 12.5x multiplier and a whopping 2818MHz Northbridge frequency. We believe that this could well be the fastest configuration we've ever achieved with this particular Phenom II X4 965 Black Edition Processor.
The above overclock was verified OCCT Linpack stable and ready for the testing regime that will soon follow...