Overclocking - The road to 4.00GHz
Our journey commences with the following variables:
HTT Base Frequency: 200MHz
CPU Multiplier: 17x
CPU Voltage: 1.4000V
Northbridge Multiplier: 10x (2000MHz)
HT Link Frequency: 2000MHz
DRAM Frequency: 1333MHz
Overall Clockspeed: 3400MHz
Our particular AMD Phenom II X4 965BE had defaulted to 1.400V. We were a little perplexed by this given that the processor is meant to have a TDP of 125W, which typically means a CPU voltage of 1.3500V to 1.3750V with an AMD Phenom II processor. For our own interest we "undervolted" the processor to 1.3500V and was able to run stability tests all day long. To make things a little more juicy we kept the processor at this voltage while overclocking.
We started by raising the CPU Mutiplier in 0.5x increments and for each clock speed increase, OCCT's CPU Test was ran for 5 minutes to detect any horrific levels of instability. The process was smooth until our system restarted after a more extensive stability testing session at 3.80GHz. A 400MHz overclock at less than stock speeds? Not too shabby. A voltage of 1.400V was required to run the OCCT Linpack test stable for the whole hour duration.
After a 0.0500V increase to 1.4000V, we had successfully met the 4.00GHz barrier. Sadly, it took less than 30 seconds of OCCT's Linpack test for the system to reboot.
After minor adjustments to the CPU Multiplier, Base HTT Frequency and CPU Voltage, we attained a maximum frequency of 3.940GHz with an effective 1.5250V applied in BIOS. All in all, a 60MHz decrement and a 0.1000V Voltage increase from 4.00GHz was commanded for a stable overclock. This may well be a new stepping but the typical Overclock Wall strikes again. The overclock however was completely stable and following an hour of OCCT Linpack, it was able to run Prime95's Blend test for a further three hours before we halted the test. This by all intents and purposes is a stable setup for the typical user however it's open to debate as to how much stability testing is truly required as it'll depend on the system's usage. If for example, the processor is working flat out running distributed computing projects such as Folding@Home then one would want to be running stability tests for a far longer period of time, but then again this doesn't constitute normal system activity.
Further increases in CPU Voltages would raise it's temperatures past sensible margins and so it was decided to open a window, taking ambient temperatures to a chillier 15c. After trying different combinations of CPU HTT and CPU Multi, incremented Northbridge and HT Link Voltages as well as adjusted Advanced Clock Calibration (which shouldn't even help for this processor), this particular Deneb had no more to offer. We were however also able to increase the processor's memory controller frequency from it's default 2000MHz to 2424MHz.