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Making The Most Of Limited Overclocking

System Builder Marathon, March 2012: $650 Gaming PC
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With no access to base clock settings, a locked processor multiplier, and memory data rates that top out at 1333 MT/s, we're limited to pushing lower latencies. DRAM voltage settings are available in increments of one-tenth of a volt, from 1.5 V up to 2.2 V. At 1.6 V, our inexpensive kit rated for CAS 9 timings was fully stable at 7-8-7-22 1T. Despite dialing-in and testing the memory, our discussion of tuning is far from over, though. 

I have hundreds of system builds under my belt, and I’ve never witnessed such quirky behavior when changing memory timings as what I saw from Gigabyte’s DualBIOS UEFI. Every attempt to make a latency change was met with a series of rapid beeps, followed by a power-down and restart with the new settings applied. Even going from Auto to Quick, without altering anything, invoked the same behavior.

The cycle looked a lot like the recovery you'd see after a failed overclock, only it was a lot faster, and the settings actually stuck. The platform would boot fine after that until another setting was altered.

The XFX Radeon HD 6950 was fully stable at AMD Overdrive’s maximum available 840 MHz core and 1325 MHz memory frequencies. Despite such modest limits, I stayed consistent with past builds and stuck to AMD's driver rather than exploring the hardware's true ceiling using third-part software. I tend to be conservative with memory clocks, and since there was no way to know the RAM's actual limit, I dialed back to a 1300 MHz memory frequency and retailed the 840 MHz core. This minor 5% core and 4% memory overclock does handicap the current rig some, as December’s Radeon HD 6870 enjoyed a more significant 10% core and 12.4% memory overclock.

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