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Overclocking

System Builder Marathon, Sept. 2010: $2000 Performance PC
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After trying various methods to overclock our AMD Phenom II X6 1055T processor without changing its multiplier, we decided to see how far its reference clock would go. Setting it to the highest-available VDD voltage, lowest memory ratio, and a low 10x multiplier, we found that a reference clock of 290 MHz was stable.

Next, we began increasing the CPU clock multiplier until we reached its 14x limit, and again found the CPU to be stable. Unfortunately, the system had trouble rebooting. Selecting a reference clock of 288 MHz solved the reboot issue.

With our CPU frequency limited mostly by its reference clock, we began backing down the VDD voltage until we found the lowest stable setting. While we were testing various CPU voltage levels, we increased our DRAM voltage and found that 1.60 V allowed a 1:2.66 DRAM ratio for a resulting DDR3-1533 data rate.

Using our intended 1.65 V memory voltage limit allowed our modules to be reduced to 7-7-6-20 timings, while retaining the high DDR3-1533 data rate. We think this combination of speed and timings is quite good for an 8 GB set of modules rated at DDR3-1333 CAS 9.

CPU-Z confirms our speeds and timings, with the CPU at 4028 MHz.

With our CPU and DRAM settings locked in through the BIOS and completely tested for stability, it was time to see how far our graphics cards could be pushed. While Nvidia System Tools allows clock and fan speeds to be set at a constant rate, MSI’s Afterburner utility adds advanced fan controls for automatic adjustment, eliminating the constant noise of high fan speeds when temperatures are relatively low.

While it’s possible to keep previously-set clock speeds without starting the utility at every boot, the utility must run constantly for our fan speed map to apply. Two settings allow the utility to start with windows while minimized to the task bar.

We increased the GeForce GTX 480 core clock from 700 to 816 MHz, and pushed its memory from GDDR5-3696 to GDDR5-4132. Stability was tested at an ambient temperature of 27° Celsius, and a cooler workspace would have allowed us to push for even higher clock speeds.

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